Development of New Chiral Brønsted Acid Catalysis

Shin ─ ichi Hirashima ＊ and Hisashi Yamamoto ＊

Molecular Catalyst Research Center, Chubu University 1200 Matsumoto ─ cho, Kasugai 487 ─ 8501, Japan

(Received June 26, 2013; E ─ mail: [email protected]; [email protected])

Abstract: Brønsted acid catalysis has received considerable attention in modern organic synthesis. However, the utility of these Brønsted acid catalysts are somewhat limited toward applicable substrates due to its relatively lower reactivities of these Brønsted acids. With these perspectives, it is highly desirable to develop Brønsted acids demonstrating both high reactivities and selectivities. In this feature article, we will describe our achieve- ment in the design and development of Lewis acid assisted Brønsted acid catalysts (LBA), Brønsted acid assisted Brønsted acid catalysts (BBA), strong Brønsted acid catalysts, and their applications.

activity of silica ─ supported AlCl 3 arose from Lewis acid acti- 1． Introduction vation of the Brønsted acidic site on the silica surface (Fig- Brønsted acids have long been utilized in organic chemi- ure 2). 3 stry. However, their early application was rather limited to fundamental types of reactions, such as hydrolysis and formation of esters and acetals. The synthetic utility of Brønsted acids as catalysts for carbon ─ carbon bond formation reactions has been limited until quite recently. 1 This limited application Figure 2. Brønsted acidity arising from Lewis acid complex on a silica surface. of Brønsted acids in carbon ─ carbon bond formation reactions was probably due to the unavailability of Brønsted acids with Classic acid ─ catalyzed reactions, such as the addition of suitable reactivity, which results in poor functional group toler- HCl to alkenes, often show a second ─ order dependence on the ance and unexpected side ─ reactions. acids. In that sense, the involvement of dimeric acids such as To address this challenging issue, we started research in the HCl…HCl might be speculated (Figure 3). 4 The same principle design and development of strong Brønsted acids. We pro- of activation of Brønsted acids plays an important role in posed a “combined acid system” between Brønsted acid/Lewis many cases, a number of which are regarded as Brønsted acid acid and Brønsted acid/Brønsted acid catalysis both intermo- assisted Brønsted acid systems. lecularly and intramolecularly, which is now the general con- cept for designing acid catalysts for asymmetric reactions. Moreover, we developed new strong Brønsted acids, which are chiral N ─ tri yl oxo ─ , thio ─ , and seleno ─ phosphoramides. Herein we wish to describe our efforts towards the development of strong Brønsted acids and their applications. 2． Combined Acid Catalysis Figure 3. Plausible involvement of dimeric acids in acid ─ catalyzed Coordination of a ketone or aldehyde to a Lewis acid can addition of HCI to alkenes. promote enolization by virtue of the enhanced acidity of the α ─ hydrogen atoms in the complex. The practical utility of These combined acid catalysts can be classied as shown in these types of Lewis acid activation is well developed. For Table 1. It should be emphasized that we anticipated a more or

example, changes in acidities of up to 24 pK a units are observed less intramolecular assembly of such combined systems rather by combining the measured gas ─ phase acidities with the calcu- than intermolecular arrangements. Thus, a correct design of 2 lated solvation energies for these species (Figure 1). This the catalyst structure is essential for success. example can be described as a typical case for a Lewis acid activation of a weak Brønsted acid. Table 1. The general classications of combined acid catalysis.

Figure 1. Lewis acid activation of a weak Brønsted acid.

Similar activations can be readily found in various reports of combined acid complexes. Clark showed that the catalytic

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有機合成化学71-11＿04論文_Hirashima.indd 8 2013/10/21 10:56:36 2.1 Lewis Acid Assisted Brønsted Acid Catalysts (LBAs) We demonstrated that the synthetic utility of LBAs applied The combination of Lewis acids and Brønsted acids gives to the regio ─ and stereoselective isomerization of a “kinetic” Lewis acid assisted Brønsted acid catalysts and provides an silyl enol ether to a “thermodynamic” one catalyzed by an opportunity to design a “unique proton”, 5 that is, the coordina- achiral LBA (Scheme 3). 8 “Kinetic” TBS enol ethers were tion of a Lewis acid to the heteroatom of the Brønsted acid isomerized to “thermodynamic” species by the coordinate

could increase the acidity of the latter. complexes of SnCl 4 catalyst and the monoalkyl ethers of In 1994, we reported that chiral LBAs can be generated in biphenol. For the various structurally diverse substrates, the

situ from optically pure BINOL and SnCl 4 in toluene and is isomerization proceeded cleanly in the presence of 5 mol% of stable in solution, even at room temperature. 6 The protonation the achiral LBA. of the silyl enol ether derived from 2 ─ phenylcyclohexanone afforded the S isomer with 97% ee in the presence of a stoi- Scheme 3. Isomerization of silyl enol ethers catalyzed by achiral LBA. TBS = tert butyldimethylsilyl. chiometric amount of (R) ─ LBA (Scheme 1). This LBA reagent ─ could be also applicable to various ketene bis(trialkylsilyl)acetals derived from α ─ aryl carboxylic acids. The sense of stereoinduction can be understood in terms of the proposed transition ─ state assembly shown in Scheme 1. The trialkylsiloxy group is directed opposite to the binaphthyl moiety to avoid any steric interaction, and the aryl group is stacked on this naphthyl group. In further studies, enantioselective protonation with a stoichiometric amount of an achiral proton source and a catalytic amount of the chiral LBA was possible (Scheme 2). 6b,7

In 2003, optically active 1,2 diarylethane 1,2 diol·SnCl Scheme 1. Enantioselective protonation with chiral LBA generated ─ ─ ─ 4 derivatives were designed as a new type of LBA for enantiose- from (R) ─ BINOL and SnCl 4. lective protonation (Scheme 4). 9 A variety of optically active 1,2 ─ diarylethane ─ 1,2 ─ diols could be readily prepared by asymmetric syn dihydroxylation, which is advantageous to the use of BINOL for the exible design of a new LBA. The most signicant nding is the identication of the conformational direction of the H─ O bond of LBA by X ─ ray diffraction analysis (Figure 4). The stereochemical outcome of the enantioselective protonation of silyl enol ethers with this LBA could be controlled by a liner OH ─ π interaction with in the initial step (Scheme 4). In 1999, we successfully developed the rst enantioselective biomimetic cyclization of polyprenoids catalyzed by chiral LBA (Scheme 5). 10 We found that the tricyclic ethers were obtained from geranyl phenyl ethers, o ─ geranylphenols, and geranylacetone derivatives using (R) ─ BINOL derivatives and

SnCl 4. The reaction proceeded smoothly even in catalytic

Scheme 2. Catalytic enantioselective protonation with chiral LBA Scheme 4. Enantioselective protonation with chiral LBA generated from chiral hydrobenzoin derivative and SnCl . generated from monoprotected BINOL and SnCl 4. 4

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有機合成化学71-11＿04論文_Hirashima.indd 9 2013/10/21 10:56:37 amounts of the chiral LBA and often took place via [1,3] ─ Claisen ─ type rearrangements using geranyl phenyl ethers as substrates. The best result of 90% ee was observed for the cyclization of p ─ bromophenyl geranyl ether. This LBA approach was also applied to the enantioselective cyclization

of homo(polyprenyl)arenes by (R) ─ BINOL ─ o ─ F ─ Bn·SnCl 4 11 (Scheme 5). Several optically active podocarpa ─ 8,11,13 ─ tri- ene diterpenoids and (-) ─ tetracyclic polyprenoids of sedimen- tary origin were synthesized by the enantioselective cyclization of homo(polyprenyl)benzene derivatives induced by this LBA and subsequent diastereoselective cyclization induced by

BF 3·Et 2O or CF 3CO 2H·SnCl 4 (75 ─ 80% ee). Moreover, the synthetic utility of LBA catalysts was demonstrated by very efcient route to (-) ─ 11’ ─ deoxytaondiol methyl ether. Figure 4. X ─ ray structure of LBA generated from monomethylated Very recently, Corey and co ─ workers reported the enanti- chiral hydrobenzoin and SnCl 4 (the O1 ─ H act bond distance shown here is not certain, but its direction could be deter- oselective proton ─ initiated polycyclization of polyenes by the 12 mined). Selected distances ( Å ): O1 ─ H act = 0.72(3), Sn1 ─ 1:1 complex of o,o’ ─ dichloro ─ BINOL and SbCl 5 (Scheme 6). Cl3 = 2.40185(5), Sn1 ─ Sl4 = 2.3522(6), intermolecular This LBA reagent afforded the polycyclized products in high H act…Cl3 = 2.402. Torsion angles (deg): Cl3 ─ Sn1 ─ H act = yields (up to 89%) and enatioselectivity (up to 92% ee). -64, Cl1 ─ Sn1 ─ O1 ─ H act = 30. Bond angles (deg): Sn1 ─ O1 ─ 2.2 Brønsted Acid Assisted Brønsted Acid Catalysts (BBAs) H ac = 119(20, C2 ─ O1 ─ H act = - 64(2), intermolecular O1 ─ H act…Cl3 = 171.11. Hydrogen bonding plays a crucial role in the organization of the three ─ dimensional structure of enzymes and is often

Scheme 5. Biomimetic cyclizations catalyzed by chiral LBAs.

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有機合成化学71-11＿04論文_Hirashima.indd 10 2013/10/21 10:56:38 Scheme 6. Enantioselective polycyclization by Alder reactions of a wide range of aliphatic and aromatic 17 (R) ─ o ,o’ ─ dichloro ─ BINOL·SbCl 5. aldehydes (Scheme 7). This BBA catalyst can share with TADDOLs the bis(diarylhydroxymethyl) functionality, in which the steric and electronic properties are readily tunable. The axial chirality in BAMOL provides further opportunity for tweaking the chiral environment. The X ─ ray crystal structure not only shows a 1:1 complex of BAMOL and benzaldehyde, but also reveals the presence of an intramolecular hydrogen bond between the two hydroxyls and an intermolecular hydrogen bond to the carbonyl oxygen of benzaldehyde (Fig- ure 7). involved in the reaction at the active site. An ideal example is a concerted proton transfer in the rate ─ limiting step of heme Scheme 7. Asymmetric Diels ─ Alder reactions catalyzed by BBA oxygenase catalysis (Figure 5). 13 catalysts.

Figure 5. Concerted proton transfer in the rate ─ limiting step of heme oxygenase.

Such an elegant principle could be applicable to asymmetric catalysis. Especially for Brønsted acid catalysis, the design of these catalysts would result not only in the formation of a highly organized chiral cavity but also in an increase in the Brønsted acidity of the terminal proton in a much milder way than that of the LBA system. An example of intramolecular hydrogen bonding is also observed in the small organic molecule TADDOL (tetraaryl ─ 14 1,3 ─ dioxolane ─ 4,5 ─ dimethanol) (Figure 6), which is one of the most efcient chiral backbones for asymmetric synthesis. Within this molecule, one of the hydrogen atom of the order one is free for intermolecular interactions. These unique fea- tures have been conrmed by X ─ ray crystallographic analysis.

Figure 6. Intramolecular hydrogen bonding within TADDOL.

Rawal and co ─ workers utilized this excellent candidate as a 15 chiral BBA catalyst. They reported that hetero ─ Diels ─ Alder reactions by TADDOL are highly enatioselective and generate Figure 7. X ─ ray crystal structure of BAMOL ─ enzaldehyde complex. only one of the enantiomers of the dihydropyran product (Scheme 7). This type of catalysis mimics the action of enzyme We documented that both the appropriated amine frame- and antibodies, in contrast to traditional, metal ─ based cata- work of enamine and the proper choice of acidity of Brønsted lysts used in organic chemistry. An interesting feature of this acid catalyst play contributing roles in O/N regioselectivities in catalyst is that the monomethyl ether derivatives of TADDOL nitroso aldol (NA) reaction: the chiral alcohol exhibits com- showed poor enantioselectivity, indicating that the intramole plete N ─ selection and a high enantioselection with piperidine cular hydrogen bonding network within the catalyst must be or morpholine enamine. For N=O group, an alcoholic proton crucial for higher asymmetric induction. reinforces coordination to the mutually preferred nitroso oxy- The TADDOL catalyst is also highly effective for the enan- gen. In contrast, the chiral carboxylic acid catalyst exhibits tioselective Diels ─ Alder reactions of α, β ─ unsaturated alde- uniformly high O ─ selectivity and enantioselectivity depending 16 18 hydes (Scheme 7). After the two ─ step transformations from on the amine structure of enamine (Scheme 8). The absolute the initial cycloadducts, a variety of chiral cyclohexenones conguration of N ─ NA product can be explained by the were obtained with high enantioselectivies (up to 92% ee). hydrogen bonding activation of nitroso derivative by (R,R) ─ Furthermore, our group and the Rawal group have found that TADDOL (Ar=phenyl) reported by Połoński and co ─ workers 19 the axially chiral BAMOL (1,1’ ─ biaryl ─ 2,2’ ─ dimethanol) scaf- (Figure 8). fold to be highly effective for the catalysis of the hetero ─ Diels ─ Chiral BINOL ─ derived Brønsted acids catalyze diastereo ─

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有機合成化学71-11＿04論文_Hirashima.indd 11 2013/10/21 10:56:39 Scheme 8. Brønsted acid catalysis of achiral enamine in nitroso aldol (NA) synthesis. 3． Design of Strong Chiral Brønsted Acids 3.1 Chiral N Tri yl Oxo phosphoramides Since Akiy─ama 21 and Te─rada 22 independently accomplished an innovative approach to the development of chiral BINOL ─ derived phosphoric acid catalysts in 2004, it soon became clear that they possessed tremendous potential to activate electrophiles towards nucleophilic attack in asymmetric catalysis. 23 Although many successful enantioselective addition reactions to imines have been achieved with these Brønsted acids, the utility of these acids to the activation of other functional groups are somewhat limited due to relatively lower reactivities of these Brønsted acids. The activation of unfunctionalized carbonyl groups with these Brønsted acids has remained challenging. We envisioned that increasing the acidity of the phosphoric acid would overcome these limitations and further extend the use of this catalyst beyond imine electrophiles. The acidity of the Brønsted acid can be increased by introduction of a strong electron ─ withdrawing group, such as N ─ tri uoro- methanesulfonyl (N ─ tri yl) group, which can stabilize the con- Figure 8. Crystal structure of (R,R) ─ TADDOL ─ nitrosoamine. jugate base. Koppel and co ─ workers demonstrated signicant increases in acidity of Brønsted acids by introduction of the strong electron withdrawing N tri yl group. 24 Introduction of Scheme 9. Diastereo ─ and enantioselective synthesis of nitroso ─ ─ Diels ─ Alder type bicycloketones by chiral BBA. the N ─ tri yl group in carboxylic acid increases the acidity by 9 almost 10 times, for instance; the pK a values of N ─ tri yl benz- amide and benzoic acid in acetonitrile are 11.06 and 20.7, respectively. Thus, similar acidity enhancement would be expected to be achieved by simple introduction of the N ─ tri yl group into the P=O group in the phosphoric acid (Scheme 10). 25

Scheme 10. Enhancement of acidity of a phosphoric acid by introduction of the N ─ tri yl group.

Based on this idea, we have developed N ─ tri yl oxo ─ phos- and enantioselective synthesis of nitroso Diels ─ Alder ─ type phoramide as a strong Brønsted acid, which can be readily bicycloketones through sequential NA ─ Michael reaction prepared. X ─ ray crystallography analysis revealed that the 20 (Scheme 9). Brønsted acid has P=O bond and P ─ N single bond and the The transition ─ state in Figure 9 provides an attempt to proton is located on the N atom rather than on the O atom as rationalize the observed sense of stereoinduction and transfor- shown in Figure 10. 26 mation. The overall hydrogen bond network between the two hydroxyls of the chiral BINOL via BBA system and nitroso oxygen could be the dominant factor accounting for the observed diastereo ─ and enantioselectivies. The bulky arylsilyl group would not allow it to attack diene from the Si face due to the steric inhibition with substituents of dienamine at the 4─ position.

Figure 10. Crystal structure of N ─ tri yl oxo ─ phosphoramide.

We successfully applied this Brønsted acid to the catalytic Figure 9. Plausible transition state in chiral BBA catalyzed reaction. asymmetric Diels ─ Alder reaction of ethyl vinyl ketone with

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有機合成化学71-11＿04論文_Hirashima.indd 12 2013/10/21 10:56:40 siloxydienes, which is the rst example of activation of car- cycloaddition reaction gave the desired product with high endo bonyl functionality in phosphoric acid catalysis. 25 Introduction selectivity (Scheme 13). of the N ─ tri yl group dramatically increased the reactivity: N ─ The dramatic difference in diastereoselectivity between the tri yl phosphoramide gave the Diels ─ Alder adducts in excel- [3+2] cycloaddition catalyzed by the Brønsted acid (up to 97% lent yields and enantioselectivities, whereas phosphoric acid endo selective) and MeAl ─ BINOL complex (up to＞95% exo showed no catalytic activity (Scheme 11 and Table 2). selective) can be rationalized by transition ─ state structure (Figure 11). For the Lewis acid catalyzed cycloaddition reac- Scheme 11. Reactivity comparison of asymmetric Diels ─ Alder tion, the exo approach would be favored due to the steric reaction of ethyl vinyl ketone with siloxydienes. repulsion between the alkoxy group and the bulky Lewis acid, whereas for the Brønsted acid catalyzed reaction the much smaller proton allows endo approach. Moreover, the hydrogen bonding between the proton of the Brønsted acid and the oxygen atom of ethyl vinyl ether may provide stabilization in the endo selective transition ─ state.

Scheme 13. Difference in diastereoselectivity between Brønsted acid and Lewis acid catalyzed 1,3 ─ dipolar cycloaddition of nitrones. Ad = adamantyl.

Table 2. Asymmetric Diels ─ Alder reaction of ethyl vinyl ketone with siloxydienes by N ─ tri yl oxo ─ phosphoramide.

Interestingly, we observed a signicant difference in reactivity between this Brønsted acid and its silylated catalyst. The same reaction using N ─ tri yl oxo ─ phosphoramide, pretreated with TIPS enol ether of acetophenone, gave no desired product (Scheme 12); silyl Lewis acid has no catalytic activity. This result suggested that the reaction proceeded by direct activation of the carbonyl compound by the Brønsted acid. This might be responsible for the high enantioselectivity in this reaction since silicon cation is generally known to be less selective in asymmetric reactions. 27 We extended the utility of N ─ tri yl oxo ─ phosphoramide to the enantioselective 1,3 ─ dipolar cycloaddition of nitrones with ethyl vinyl ether. 26 It should be noted that in sharp contrast to the exo selectivity of Lewis acid catalyzed cycloaddition of Figure 11. Plausible transition ─ states showing the diastereoselectivity of the Lewis and Brønsted acid cata- diaryl nitrones with alkyl vinyl ether reported by Jørgensen lyzed 1,3 dipolar cycloaddition. 28 ─ and co ─ workers, this N ─ tri yl oxo ─ phosphoramide catalyzed

Scheme 12. Deactivation fo Brønsted acid.

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有機合成化学71-11＿04論文_Hirashima.indd 13 2013/10/21 10:56:41 3.2 Chiral N ─ Tri yl Thio ─ and Seleno ─ phosphoramides The reactivities and enantioselectivities were strongly After our development of chiral N ─ tri yl oxo ─ phos- dependent on the achiral Brønsted acid and higher enantiose- phoramide proved successful, other groups reported several lectivities could be achieved with less hindered phenol or car- asymmetric reactions with the Brønsted acid. 29 However, the boxylic acid derivatives. The best result in terms of catalytic utility of this N ─ tri yl oxo ─ phosphoramide to the activation activity and enantioselectivity was observed when phenol was of the other functional groups are still limited. Thus, we con- employed as an achiral proton source. Although the protona- tinued efforts to make the utility of chiral phosphoric acid cat- tion of silyl enol ethers derived from cyclic ketones having an alysts more general in organic synthesis by the design of a new aliphatic substituent at the α ─ position gave moderate enantio- chiral Brønsted acid with higher acidity. In general, acidity selectivities, silyl enol ethers derived from 2 ─ aryl cyclic ketones increases going down a column in the periodic table due to provided the desired protonated products in excellent yields better stabilization of the conjugate base in a more polarizable and high enantioselectivities (Table 4). Furthermore, the cata-

atom. For instance, the pK a value of PhOH, PhSH, and PhSeH lyst loading could be reduced to 0.05 mol% without loss of in DMSO are 18.0, 10.3, and 7.1, respectively. 30 We expected enantioselectivity. that simple substitution of the oxygen in P=O bond in the N ─ tri yl oxo ─ phosphoramide with sulfur and selenium would Table 4. Asymmetric protonation reaction of silyl enol ethers by increase the acidity (Scheme 14). 31 Based on this idea, we have chiral N ─ tri yl thio ─ phosphoramide. developed N ─ tri yl thio ─ and seleno ─ phosphoramides as strong chiral Brønsted acids.

Scheme 14. Enhancement of acidity by introduction of a more polarizable atom in N ─ tri yl oxo ─ phosphoramide.

We documented that these new Brønsted acids are highly effective for an enantioselective protonation reaction of silyl enol ethers. 32 To compare the catalytic reactivity of various chiral Brønsted acids, the enantioselective protonations of the silyl enol ether were investigated in the presence of a stoichio- As illustrated in Scheme 15, we believe that the protonation metric amount of 2,4,6 ─ trimethylbenzoic acid as an achiral reaction proceeds through a two ─ step sequence: the enantiose- Brønsted acid (Table 3). It is noteworthy that almost no reac- lective protonation reaction proceeds from either the chiral tion was observed using the chiral phosphoric acid and thio ─ Brønsted acid or the chiral oxonium ion pair generated by phosphoric acid. However, N ─ tri yl oxo ─ phosphoramide is rapid proton transfer between the chiral Brønsted acid and crucial to enhance the catalytic activity: this Brønsted acid achiral proton to silyl enol ether to form an intermediary chiral gives the desired product with quantitative yield and moderate ion pair, following to afford the corresponding protonated enantioselectivity. Moreover, we found that substitution of the ketone and regenerate the catalyst by the desilylation with the oxygen with sulfur or selenium in the N ─ tri yl oxo ─ phos- achiral proton source. phoramide, N ─ tri yl thio ─ or seleno ─ phosphoramide catalyst, improved enantioselectivity as well as reactivity. Scheme 15. Plausible path of an enantioselective protonation reaction. Table 3. Reactivity comparison of Brønsted acid in enantioselective protonation reaction.

Although Lewis acid 33 and Lewis base 34 catalyzed asymmetric Mukaiyama aldol reactions have been widely developed, only a few examples of chiral Brønsted acid catalyzed enantioselective Mukaiyama aldol reactions have been reported. 35 However, these reactions generally required highly activated substrates. In 2009, List and co ─ workers have developed a chiral sulfonimide as a new strong Brønsted acid and successfully

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有機合成化学71-11＿04論文_Hirashima.indd 14 2013/10/21 10:56:42 37 it catalyzed asymmetric Mukaiyama aldol reactions of unfunc- using N ─ tri yl thio ─ phosphoramide catalyst (Table 5). The 36 tionalized aldehydes with silyl ketene acetals as nucleophiles. N ─ tri yl thio ─ phosphoramide provided the desired aldol They reported that the active species were shown to be the N ─ product in excellent yields (up to 98%) and high enantioselec- silyl imide acting as Lewis acid rather than Brønsted acid itself. tivities (up to 94% ee). In 2010, we demonstrated that the rst enantioselective “Brøn- It is clear that the substituent of 3,3’ ─ position of BINOL sted acid catalyzed” Mukaiyama aldol reaction of aldehydes scaffold is crucial to provide a chiral environment around acidic proton as a substrate recognition site. The substituent sometimes in uences reactivity and/or enantioselectivity due Table 5. Enantioselective Mukaiyama aldol reaction of aldehyde by to adjust not only sterically but also electronically. The sub- chiral N ─ tri yl thio ─ phosphoramide. stituents of 3,3’ ─ position of BINOL, which have been developed by many researchers, are shown in Table 6. 21,22,26,32,38 In the enantioselective Mukaiyama aldol reaction, the bulky substituent, 9 ─ anthracenyl, at the 4 ─ position of 3,3’ ─ aryl substituent of the BINOL improved both diastereoselectivity and enantioselectivity. Mechanistic details revealed that the actual catalyst could be changed from the Brønsted acid to the silyl Lewis acid depending on the reaction temperature (Scheme 16). This result suggested that at room temperature the silyl Lewis acid catalyzed pathway would be operative, whereas at low temperature the Brønsted acid directly activates the carbonyl compound. Therefore, the Brønsted acid catalyst is more reactive and selective compared with the corresponding silicon ─ cen- tered Lewis acid catalyst.

Table 6. Library of 3,3’ ─ substituents of Brønsted acids.

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有機合成化学71-11＿04論文_Hirashima.indd 15 2013/10/21 10:56:43 Scheme 16. Mechanistic study of the enantioselective Mukaiyama Yamamoto, H. J. Am. Chem. Soc. 2004, 126, 11122. aldol reactions. 12） Surendra, K.; Corey, E. J. J. Am. Chem. Soc. 2012, 134, 11992. 13） Davydov, R.; Matsui, T.; Fujii, H.; Ikeda ─ Saito, M.; Hoffman, B. M. J. Am. Chem. Soc. 2003, 125, 16208. 14） For an excellent review, see: Seebach, D.; Beck, A. K.; Heckel, A. Angew. Chem. 2001, 113, 96; Angew. Chem. Int. Ed. 2001, 40, 92. 15） Huang, Y.; Unni, A. K.; Thadani, A. N.; Rawal, V. H. Nature 2003, 424, 146. 16） Thadani, A. N.; Stankovic, A. R.; Rawal, V. H. Proc. Natl. Acad. Sci. USA, 2004, 101, 5846. 17） Unni, A. K.; Takenaka, N.; Yamamoto, H.; Rawal, V. H. J. Am. Chem. Soc. 2005, 127, 1336. 18） Momiyama, N.; Yamamoto, H. J. Am. Chem. Soc. 2005, 127, 1080. 19） (a) Olszewska, T.; Milewska, M. J.; Gdaniec, M.; Połoński, T. Chem. Commun. 1999, 1385. (b) Olszewska, T.; Milewska, M. J.; Gdaniec, M.; Małuszyńska, H.; Połoński, T. J. Org. Chem. 2001, 66, 501. 20） Momiyama, N.; Yamamoto, Y.; Yamamoto, H. J. Am. Chem. Soc. 2007, 129, 1190. 21） Akiyama, T.; Itoh, J.; Yokota, K.; Fuchibe, K. Angew. Chem. Int. Ed. 2004, 43, 1566. 22） Uraguchi, D.; Terada, M. J. Am. Chem. Soc. 2004, 126, 5356. 4． Conclusions 23） For recent reviews, see: (a) Akiyama, T.; Itoh, J.; Fuchibe, K. Adv. Synth. Catal. 2006, 348, 999. (b) Doyle, A. G.; Jacobsen, E. N. Chem. This article focused on our progress in the chemistry of Rev. 2007, 107, 5713. (c) Akiyama, T. Chem. Rev. 2007, 107, 5744. (d) chiral Brønsted acid catalysis for enantioselective transforma- Terada, M.; Chem. Commun. 2008, 4097. (e) Adair, A.; Mukherjee, S.; List, B. Aldrichimica Acta. 2008, 41, 31. (f) Yamamoto, H.; Payette, N. tions. The synthetic utility of Brønsted acids as catalysts has In “Hydrogen Bonding in Organic Synthesis” ed. by Pihko, P. M. been limited compared with Lewis acid catalysis. This limited Wiley ─ VCH: Weinheim, 2009, p 73. (g) Terada, M. Bull. Chem. Soc. application of Brønsted acids was probably due to the lack of Jpn. 2010, 83, 101. (h) Kampen, D.; Reisinger, C. M.; List, B. Top. sufcient acidity. We have demonstrated that development of Curr. Chem. 2010, 291, 395. (i) Terada, M. Synthesis 2010, 1929. (j) Terada, M. Curr. Org. Chem. 2011, 15, 2227. (k) Akiyama, T. J. Synth. new chiral Brønsted acids by a structural design provides the Org. Chem., Jpn. 2011, 69, 913. (l) Cheon, C. H.; Yamamoto, H. solution to extend the scope of Brønsted acid catalysis. Further Chem. Commun. 2011, 47, 3043. (m) Terada, M. J. Synth. Org. Chem., studies on the rational design of chiral Brønsted acid catalysts Jpn. 2013, 71, 480. 24） (a) Leito, I.; Kaljurand, I.; Koppel, I. A.; Yagupolskii, L. M.; Vlasov, may lead to practical articial enzymes and green innovations. V. M. J. Org. Chem. 1998, 63, 7868. (b) Koppel, I. A.; Koppel, J.; Leito, I.; Koppel, I.; Mishima, M.; Yagupolskii, L. M. J. Chem. Soc., Acknowledgements Perkin Trans. 2 2001, 229. (c) Yagupolskii, L. M.; Petril, V. N.; We deeply acknowledge our co workers for their extensive Kondratenko, N. V.; Sooväli, L.; Kaljurand, I.; Leito, I.; Koppel I. A. ─ J. Chem. Soc., Perkin Trans. 2 2002, 1950. contributions to this work. This work was supported by 25） Nakashima, D.; Yamamoto, H. J. Am. Chem. Soc. 2006, 128, 9626. Grant ─ in ─ Aid for Scientic Research (No. 23225002), ACT ─ C 26） Jiao, P.; Nakashima, D.; Yamamoto, H. Angew. Chem. Int. Ed. 2008, from JST (Japan), the Uehara Memorial Foundation, Nippon 47, 2411. 27 Ishihara, K.; Yamamoto, H. Chem. Commun. 2002, 1564. Pharmaceutical Chemicals Co., Ltd, and Advance Electric ） 28） Simonsen, K. B.; Bayón, P.; Hasell, R. G.; Gothelf, K. V.; Jørgensen, Co., Inc. K. A. J. Am. Chem. Soc. 1999, 121, 3845. 29） (a) Rueping, M.; Ieawsuwan, W.; Antonchick, A. P.; Nachtsheim, B. J. References Angew. 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有機合成化学71-11＿04論文_Hirashima.indd 16 2013/10/21 10:56:44 38） (a) Storer, R. I.; Carrera, D. E.; Ni, Y.; MacMillan, D. W. C. J. Am. PROFILE Chem. Soc. 2006, 128, 84. (b) Akiyama, T.; Suzuki, T.; Mori, K. Org. Lett. 2009, 11, 2445. (c) Wanner, M. J.; Hauwert, P.; Schoemaker, H. Shin ichi Hirashima is an Assistant Professor E.; de Gelder, R.; van Maarseveen, J. H.; Hiemstra, H. Eur. J. Org. of C─hubu University. He received his B.Sc. Chem. 2008, 180. (d) Chen, Q. ─ A.; Gao, K.; Duan, Y.; Ye, Z. ─ S.; Shi, (2005) and Ph.D. degree (2010) from Gifu L.; Yang, Y.; Zhou, Y. ─ G. J. Am. Chem. Soc. 2012, 134, 2442. (e) Liu, Pharmaceutical University. After working as H.; Cun. L. ─ F.; Mi, A. ─ Q.; Jiang, Y. ─ Z.; Gong, L. ─ Z. Org. Lett. 2006, a postdoctoral fellow at the University of 8, 6023. (f) Sun, F. ─ L.; Zheng, X. ─ J.; Gu, Q.; He, Q. ─ L.; You, S. ─ L. Chicago and Chubu University with Profes- Eur. J. Org. Chem. 2010, 47. (g) Terada, M.; Yokoyama, S.; Sorimachi, sor Hisashi Yamamoto from 2010 to 2012, he K.; Uraguchi, D. Adv. Synth. Catal. 2007, 349, 1863. (h) Hatano, M.; was appointed as an Assistant Professor of Ikeo, T.; Matsumura, T.; Torii, S.; Ishihara, K. Adv. Synth. Catal. Molecular Catalyst Research Center at Chu- 2008, 350, 1776. (i) Guin, J.; Rabalakos, C.; List, B. Angew. Chem. Int. bu University. His research interests include Ed. 2012, 51, 8859. (j) Akiyama, T.; Katoh, T.; Mori, K. Angew. the development of strong Brønsted acids Chem. Int. Ed. 2009, 48, 4226. (k) Mahlau, M.; García ─ García, P.; and their application to organic reactions. List, B. Chem. Eur. J. 2012, 18, 16283. (l) Kang, Q.; Zhao, Z. ─ A.; You, S. ─ L. J. Am. Chem. Soc. 2007, 129, 1484. (m) Giera, D. S.; Sickert, M.; Schneider, C. Synthesis 2009, 22, 3797. (n) Momiyama, N.; Nishimoto, H.; Terada, M. Org. Lett. 2011, 13, 2126. (o) Akiyama, T.; Tamura, Y.; Hisashi Yamamoto received his B.Sc. from Itoh, J.; Morita, H.; Fuchibe, K. Synlett 2006, 141. (p) Seayad, J.; Kyoto University under the supervision of Seayad, A. M.; List, B. J. Am. Chem. Soc. 2006, 128, 1086. (q) Cheng, Professor H. Nozaki and R. Noyori and X.; Goddard, R.; Buth, G.; List, B. Angew. Chem. Int. Ed. 2008, 47, Ph.D. from Harvard University under the 5079. (r) Terada, M.; Machioka, K.; Sorimachi, K. Angew. Chem. Int. mentorship of Professor E. J. Corey. He held Ed. 2006, 45, 2254. (s) Rueping, M.; Antonchick, A. P.; Theissmann, academic positions at Kyoto University and T. Angew. Chem. Int. Ed. 2006, 45, 3683. (t) Xu, S.; Wang, Z.; Zhang, before he moved to Nagoya University where X.; Zhang, X.; Ding, K. Angew. Chem. Int. Ed. 2008, 47, 2840. (u) he became Professor in 1983. In 2002, he Shapiro, N. D.; Rauniyar, V.; Hamilton, G. L.; Wu, J.; Toste, F. D. moved to United States as Arthur Holly Nature 2011, 470, 245. Compton Distinguished Service Professor at the University of Chicago. In 2012, he moved back to Japan as director of Molecular Cata- lyst Research Center at Chubu University. His current interests are mainly development of new synthetic reactions in the eld of acid catalysis including designer Lewis and Brøn- sted acids, and combination of these two acid systems targeting more versatile, more selective, and more reactive catalysts, aiming at environmentally benign systems. His work has been honored with the Chemical Society of Japan Award for Young Chemist (1977), IBM Science Award (1988), the Chemical Society of Japan Award (1991), Chunichi Press Award (1992), Prelog Medal (1993), the Chemical Society of Japan (1995), Toray Sci- ence and Technology Award (1997), the Max ─ Tishler Prize (1998), Tetrahedron Chair (2002), Le Grand Prix de la Founda- tion Maison de la Chimie (2002), National Prize of Purple Medal (2002), Molecular Chirality Award (2003), Yamada Prize (2004), Tetrahedron Prize (2006), the Karl ─ Ziegler Professorship Award (2006), the Ja- pan Academy Prize (2007), Honorary Mem- ber of the Chemical Society of Japan (2008), ACS Award for Creative Work in Synthetic Organic Chemistry (2009), Grand Prize of Synthetic Organic Chemistry (2009), fellow of American Academy of Arts and Sciences (2011), Noyori Prize (2011), and Fujiwara Prize (2012).

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