Recent Developments in the Cation Pool Method

Recent Developments in the “Cation Pool” Method

1 1 2 3 Jun ─ ichi Yoshida, ＊ Yosuke Ashikari, Kouichi Matsumoto, and Toshiki Nokami

1 Department of Synthetic Chemistry & Biological Chemistry, Graduate School of Engineering, Kyoto University Nishikyo ku, Kyoto 615 8510, Japan 2 ─ ─ Faculty of Science and Engineering, Kinki University 3 4 1 Kowakae, Higashi osaka, Osaka 577 8502, Japan 3 ─ ─ ─ ─ Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University 4 ─ 101 Koyamacho minami, Tottori 680 ─ 8552, Japan

(Received July 1, 2013; E ─ mail: [email protected])

Abstract: The “cation pool” method involves the generation and accumulation of highly reactive organic cations in solution. These can serve as powerful carbon and heteroatom electrophiles in organic synthesis. Recent developments in the cation pool method including the indirect cation pool method, cation chain reactions, and integrated electrochemical ─ chemical reactions are described.

react with the organic cation. The counteranions of the organic 1． Introduction cations are derived from the supporting electrolyte that is used Organic cations such as carbenium ions and onium ions for electrolysis (usually tetraalkylammonium salts). To avoid serve as useful electrophiles in a variety of reactions in organic nucleophilic attack on the cationic center, anions which are synthesis. Usually, organic cations are generated in the pres- normally considered to be very weak nucleophiles such as - - ence of nucleophiles, because the former are often very unsta- BF 4 and B(C 6F 5) 4 are used as the counter anion. Dichloro-

ble, and to be utilized efciently should be trapped by the latter methane (CH 2Cl 2) seems to be the best solvent of those exami- immediately after generation. Therefore, reactions of organic ned, presumably because of its low viscosity even at low tem- cations suffer from limitations in the variety of usable nucleo- peratures. After electrolysis is complete, a nucleophile is added 3 philes. Nucleophiles that do not survive under the conditions to obtain the desired product (Scheme 1). Use of the LiClO 4/

of cation generation cannot be used. In contrast, organic CH 3NO 2 system also enables the generation and accumulation anions such as organolithium reagents and Grignard reagents of N ─ acyliminium ions by electrolysis in an undivided cell at are generated and accumulated in solution in the absence of 0 ℃. 4 Furthermore, an ionic liquid can be used as the reaction electrophiles. After the generation process is complete, an elec- media for electrochemical generation and accumulation of an 5 trophile is added to the solution of the pre ─ formed carbanion N ─ acyliminium ion pool at room temperature. to achieve a desired transformation. Thus, development of a new method that enables genera- Scheme 1. tion of organic cations in the absence of nucleophiles was strongly needed for expanding the scope of cation chemistry in organic synthesis. In this vein, we developed the “cation pool” method, 1 whereby organic cations are generated by the electrochemical method 2 and are accumulated in solution in the absence of nucleophiles, and are then used in subsequent reactions with nucleophiles. This paper will provide a brief outline The “cation pool” method enables easy manipulation of of this “cation pool” method, with special emphasis on recent organic cation intermediates to achieve reactions with various developments which develop new aspects of the approach. nucleophiles, but its applicability strongly depends on the stability of the cation that is generated and accumulated. To solve 2． Electrochemical Methods for Generating Organic Cations this problem, the cation ow method whereby an organic in the Absence of Nucleophiles “ ” cation is generated continuously by low temperature electroly- 2.1 Direct Cation Pool Method sis using an electrochemical ow microreactor was developed. 6 The “cation pool” method is based on the irreversible oxi- The resulting cation is immediately allowed to react with a dative generation of organic cations. In the direct cation pool nucleophile in the ow system. The use of parallel laminar ow method a cation precursor is oxidized by direct electron trans- in a ow microelectrochemical reactor enables the effective fer on the surface of the electrode. The cation precursor such generation of an N ─ acyliminium ion followed by trapping with as a carbamate is electrolyzed using an H ─ type divided cell a nucleophile. 7 The laminar ow prevents the oxidation of an equipped with an anode consisting of ne bers made from easily oxidizable nucleophile at the anode. carbon felt and a platinum plate cathode. To avoid thermal 2.2 Indirect Cation Pool Method decomposition of the cation, electrolysis should be carried out Because electrochemical reactions take place only on the at low temperatures such as -78 ℃. The resulting organic cati- surface of the electrode, the efciency of cation generation in on such as an N ─ acyliminium ion is accumulated in the solu- the “cation pool” method and the “cation ow” method is not tion in the absence of a nucleophile that we want to allow to high. To solve this problem, the indirect “cation pool” method

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有機合成化学71-11＿06論文_Yoshida.indd 28 2013/10/21 14:52:09 was developed. 8 In the indirect “cation pool” method, as shown dialkylation products due to disguised chemical selectivity. 12 in Scheme 2, an active reagent such as ArS(ArSSAr) + is gene- Supramolecular coordination with the chiral N ─ acyliminium rated from diaryldisulde (ArSSAr) and accumulated electro- ion pool allows stereoselective addition of a cyanide ion. 13 This chemically at -78 ℃ (step 1). In the next step (step 2), it is protocol was applied to an asymmetric synthesis of ropiva- allowed to react with a precursor of a cation, such as thioace- caine and its analogues. tal, to generate a “cation pool” (-78 ℃). The resulting “cation pool” is allowed to react with a nucleophile (step 3). Because Scheme 4. the cation ─ generating reactions take place in homogeneous solution, they are complete within a few minutes even at low temperatures.

Scheme 2.

N ─ Acyliminium ion pools add to a C ─ C double bond Steps 2 and 3 can also be done in ow to avoid the decom- (Scheme 5). For example, their reactions with aliphatic olens position of highly unstable organic cations. The indirect “cati- and styrene derivatives followed by treatment with triethyl- on ow” method which involves the ash generation of unstable amine give [4+2] cycloaddition products. 14 Reactions with organic cations using electrochemically generated electron ─ rich olens such as enecarbamates followed by trap- ArS(ArSSAr) + in the absence of nucleophiles and their subse- ping with carbon nucleophiles such as allyltrimethylsilane give 15 quent reactions with nucleophiles in a ow system has also three ─ component coupling products. Trapping with water been developed (Scheme 3). 9 The method can be applied to the leads to carbohydroxylation of alkenes. 16 The reactions with generation and reactions of alkoxycarbenium ions at higher vinyl ethers give polymers. The use of a ow microreactor sys- temperatures. tem enables high ─ level control of the molecular weight and molecular weight distribution without using a capping agent. 17 Scheme 3. Scheme 5.

The electrochemical reduction of an N ─ acyliminium ion 3． Generation and Reactions of Cation Pools as Carbon pool gives rise to the formation of the corresponding homo ─ Electrophiles coupling product, presumably via a radical intermediate. 18 3.1 N Acyliminium Ions However, a mechanism involving two ─ electron reduction to It is─ well known that oxidation of carbamates leads to the give the anion followed by reaction of this with the cation can- formation of N ─ acyliminium ions via dissociation of the C ─ H not be ruled out. 10 bond at the α position of nitrogen. Low ─ temperature electro- The electrochemical reduction of “cation pools” in the chemical oxidation of a carbamate gives a pool of the corre- presence of radical acceptors such as methyl acrylate leads to 18 sponding N ─ acyliminium ion, which can be characterized by formation of the corresponding addition products. A mecha- NMR and IR. The resulting N ─ acyliminium ion pool reacts nism involving radical formation by one ─ electron reduction of 3,11 with various nucleophiles as shown in Scheme 4. The “cation the cation followed by addition to a C ─ C double bond, reduc- pool” method serves as a powerful tool for parallel combinato- tion of the resulting radical to give the carbanion, and subse- rial synthesis, because organic cations generated by this quent protonation seems to be reasonable (Scheme 6). method are usually so highly reactive as to couple with a wide Radical addition to an N ─ acyliminium ion is also an inter- 19 range of nucleophiles. For Friedel ─ Crafts type reactions, esting feature of “cation pool” chemistry. Alkyl iodides react micromixing is quite effective for avoiding the formation of with an N ─ acyliminium ion pool in the presence of hexabutyl-

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有機合成化学71-11＿06論文_Yoshida.indd 29 2013/10/21 14:52:10 Scheme 6. applied to the synthesis of cephalotaxine, which is the parent compound of the antileukemic harringtonines, a group of pentacyclic alkaloids of unique structure having a nitrogen ─ containing spiro system (Scheme 9).

Scheme 9.

distannane to give the coupling products. A chain mechanism shown in Scheme 7, which involves the addition of the alkyl radical to the N ─ acyliminium ion to form the corresponding radical cation, seems to be reasonable. Benzyl radicals generated from benzylsilanes, 20 arylthiomethyl radicals from aryl- thiomethylsilanes, and aryloxymethyl radicals from aryloxy- 21 methylsilanes also react with an N ─ acyliminium ion pool to 3.2 Alkoxycarbenium Ions give coupling products. Alkoxycarbenium ions are important reactive intermediates in modern organic synthesis. It should be noted that other Scheme 7. names such as oxonium ions, oxocarbenium ions, and carboxo- nium ions have also been used for carbocations stabilized by an adjacent oxygen atom and that we often draw structures having a C ─ O double bond for this type of cation. Alkoxycarbe- nium ions are often generated from the corresponding acetals by treatment with Lewis acids in the presence of nucleophiles. In this case the concentrations of alkoxycarbenium ions are usually very low. In the cation pool method alkoxycarbenium ion pools are generated from α ─ silyl ethers by oxidative C ─ Si bond dissociation, and are accumulated in solution (Scheme 10). 24 The silyl group serves as an electroauxiliary. Arylthio groups can also serve as electroauxiliaries 25 for generation of alkoxycarbenium ion pools. 26

Scheme 10.

The use of a silyl group as an electroauxiliary 22 is also effective for the generation of N ─ acyliminium ion pools. The introduction of a silyl group decreases the oxidation potentials of carbamates, and therefore the electrolysis can be carried out more easily. Control of the regiochemistry by the silyl group is also advantageous when unsymmetrical carbamates are used. The use of two electroauxiliaries on the same carbon enables Furthermore alkoxycarbenium ion pools can also be gene- 27 sequential generation of rst one, then a second “cation pool” rated by oxidative C ─ C bond dissociation. A major advan- 23 as shown in Scheme 8. This methodology was successfully tage of this C ─ C bond dissociation approach is that a byprod- uct derived from the leaving group is not produced. Another Scheme 8. advantage is the easy generation of dications, when suitable cyclic compounds are employed as starting materials

Scheme 11.

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有機合成化学71-11＿06論文_Yoshida.indd 30 2013/10/21 14:52:12 (Scheme 11). Such dications may provide powerful intermedi- avoid the formation of glycosyl uorides. The residence time ─ ates for the construction of various molecular architectures. temperature map obtained by the indirect “cation ow” method 3.3 “ Glycosyl” Cations provides information on the stability of the intermediate, pre- The glycosyl cation has long been quoted as an intermedi- sumably the glycosyl cation stabilized by ArSSAr (Figure 1). ate in glycosylation reactions, however it has never been Anyway, if we choose appropriate conditions, the glycosylation observed by spectroscopic methods. The electrolysis of thiogly- products are obtained in good yields from various glycosyla- cosides would be expected to give the corresponding glycosyl tion donors and acceptors. cations according to Scheme 10 (Y=SAr). However, the elec- Among the many known reactive glycosylation intermedi- trolysis of thioglycosides at low temperatures followed by ates, glycosyl triates are some of the most reactive towards addition of alcohols does not give the corresponding glycosyla- chemical glycosylation. They can be successfully generated and - tion products if we use BF 4 as the counter anion (Scheme 12). accumulated electrochemically as a “glycosyl triate pool” Instead glycosyl uorides are obtained, presumably because using thioglycosides as precursor (Scheme 13). 29 These “glyco- - - glycosyl cations react with BF 4 . The use of ClO 4 as the coun- syl triate pools” react with various glycosyl acceptors to ter anion does lead to the formation of the glycosylation prod- afford glycosylation products. In particular, their reaction with ucts, but the glycosyl cation could not be detected by NMR diorganosuldes gives glycosyl sulfonium ions, which serve as spectroscopy. 26 storable intermediates for glycosylation. 30

Scheme 12. Scheme 13.

3.4 Diarylcarbenium Ions Diarylcarbenium ions are carbocations which are stabilized The indirect “cation pool” 28 and “cation ow” method 9 by two adjacent aryl groups. The “cation pools” of diarylcarbe- using ArS(ArSSAr) + can be applied to glycosylation reactions, nium ions can be prepared using diarylmethanes as precursors. - although B(C 6F 5) 4 should be used as the counter anion to However, the efciency of conversion of the latter to the corresponding diarylcarbenium ions is highly dependent on the (a) substituents on the benzene rings (Scheme 14). 31

Scheme 14.

(b)

Diarylcarbenium ions are highly reactive toward various aromatic and heteroaromatic compounds (Scheme 15). 32 Moreover, the high reactivity of these species enables us to prepare dendrimers 33 and dendronized polymers. 34 4． Generation and Reactions of Cation Pools as Heteroatom Electrophiles 4.1 Silyl Cations The cleavage of Si ─ Si bonds in disilanes leads to silyl cations. Although triorganosilyl cations are usually very unstable, silyl cations can be accumulated as “cation pools” if they bear suitable coordinating stabilizing groups. For example, the elec- Figure 1. Indirect “cation ow” method. (a) Integrated ow micro- trochemical oxidation of a disilane bearing 2 ─ pyridylphenyl reactor system for glycosylation reaction with MeOH and groups leads to the formation of a pool of the silyl cation sta- (b) effects of temperature (T ) and residence time in microreactor R1 (t R) on the yield of the glycosylation bilized by pyridyl coordination, which can be characterized by 35 product. NMR and CSI ─ MS analyses (Scheme 16).

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有機合成化学71-11＿06論文_Yoshida.indd 31 2013/10/21 14:52:14 Scheme 15. Scheme 17.

4.3 ArS ＋ Cations ArS + was assumed to be generated as an intermediate in the electrochemical oxidation of ArSSAr, 40 although some doubts were expressed as to the existence of this species in the solution phase. The 1 H NMR (-80 ℃) spectrum of the solu-

tion obtained by the anodic oxidation of ArSSAr in Bu 4NBF 4

or Bu 4NB(C 6F 5) 4/CH 2Cl 2 at -78 ℃ indicates the formation of ArS(ArSSAr) + (Scheme 18). 8 CSI MS (0 ℃) also provides Scheme 16. ─ strong evidence for the formation of ArS(ArSSAr) + (Figure 3).

Scheme 18.

Figure 3. CSI ─ MS of electrogenerated ArS(ArSSAr) + (Ar= p ─ 4.2 I + Cation FC 6H 4) in Bu 4NBF 4/CH 2Cl 2 (0.67 F/mol based on It was reported that the anodic oxidation of I 2 in acetoni- ArSSAr). + trile at 0 ℃ gave “CH 3CNI ”, although the details were not 36 claried. The species generated were characterized later by ArS(ArSSAr) + can be used as the mediator for indirect 37 + CSI ─ MS, which exhibited signals due to both CH 3CNI and cation pool and ow methods (Sections 2.2 and 3.3). + 38 + + + (CH 3CN) 2I (Figure 2). This mixture reacts as “I ” with aro- ArS(ArSSAr) can also be used as an ArS equivalent and matic compounds to give the corresponding aromatic iodides shows high reactivity toward nucleophiles. Reactions of 39 (Scheme 17). The use of micromixing is effective for the selec- ArS(ArSSAr) + with carbon nucleophiles such as aromatic tive formation of monoiodination products. In extremely fast compounds, enolizable ketones, enol acetates, ketene silyl ace- competitive consecutive reactions, such as electrophilic substi- tals, and allylsilanes give the corresponding arylthiolated tution of aromatic compounds, the product selectivity is not products (Scheme 19). 41 In addition, reactions of often determined by the kinetics because the reaction is faster ArS(ArSSAr) + with alkenes and alkynes give the correspond- than mixing. The use of micromixer solves the problem, ing diarylthiolated compounds. 42 At higher temperatures such because the marked shortening of the diffusion path in a as 0 ℃ thiouorination of alkenes and alkynes takes place. 43 micromixer results in a mixing speed unobtainable in a macro batch reactor. Scheme 19.

+ Figure 2. CSI ─ MS of electrogenerated I in Bu 4NBF 4/CH 3CN (2.0 F/mol based on I 2).

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有機合成化学71-11＿06論文_Yoshida.indd 32 2013/10/21 14:52:15 - Here the counteranion, BF 4 acts as a uoride donor. Scheme 22. As described in section 2.2, ArS(ArSSAr) + can serve as highly thiophilic reagents for the generation and accumulation of alkoxycarbenium ion from thioacetals. The reaction of a thioacetal bearing a C ─ C double bond in an appropriate position with ArS(ArSSAr) + leads to cyclization followed by trap- - - ping with F derived from BF 4 when this is the counteranion 44 - (Scheme 20). In contrast, the use of B(C 6F 5) 4 as the counteranion gives the cyclized compound bearing ArS. In this case, ArSSAr attacks the cyclized cation.

Scheme 20.

+ - catalytic amount of ArS(ArSSAr) B(C 6F 5) 4 (0.2 equiv) gives the cyclized compound as a mixture of diastereoisomers. The cation chain mechanism shown in Scheme 23 is plausible.

5． Cation Chain Reactions Based on the Cation Pool Method Scheme 23. 5.1 Cyclization of Olenic Thioacetals Using ArS + As we discussed in the previous section, the reaction of thioacetals bearing a C ─ C double bond with a stoichiometric + - amount of ArS(ArSSAr) B(C 6F 5) 4 affords the cyclized product bearing an ArS group. However, the reaction also takes + - place with only a catalytic amount of ArS(ArSSAr) B(C 6F 5) 4 (0.2 equiv) in the presence of an excess amount of ArSSAr. 44 This reaction seems to proceed by the cation chain mechanism shown in Scheme 21. The fact that the use of an excess amount of ArSSAr accelerates the reaction is consistent with this mechanism.

Scheme 21.

6． Reaction Integration Based on the Cation Pool Method 6.1 Integrated Electrochemical Chemical Oxidation via Alkoxysulfonium Ions ─ Reaction integration 47 greatly enhances the power and capability of organic synthesis, because it combines multiple reactions in a single operation in one pot or in a ow system without isolation of the intermediates. The “cation pool” method enables reaction integration via unstable reactive organic cations. For example, alkoxysulfonium ions, which are key interme- 48,49 5.2 Cyclization of Dienes Using ArS + diates of the Swern ─ Moffatt type oxidation, and Kornblum The addition of ArSSAr to alkenes also takes place with a oxidation, 50,51 can be used as intermediates in the integration + - 45 52 catalytic amount of ArS(ArSSAr) B(C 6F 5) 4 . On the other of electrochemical oxidation and chemical oxidation. Carbo- - 31,32 hand if BF 4 is used as the counteranion, the reaction requires cations, such as diarylcarbenium ions generated by oxida- a stoichiometric amount of ArS (ArSSAr) +. In the former case tive C ─ H bond dissociation using the “cation pool” method the reaction seems to proceed by the cation chain mechanism react with dimethyl sulfoxide (DMSO) to give alkoxysulfonium shown in Scheme 22. The addition of ArS(ArSSAr) + to a C ─ C ion pools, which have been well characterized by NMR. After double bond gives the episulfonium ion intermediate, which electrolysis, treatment with triethylamine gives the correspond- reacts with ArSSAr to give the addition product. In the nal ing carbonyl compounds (Scheme 24). If the cationic interme- step, ArS(ArSSAr) + is regenerated, which enables the next diates are unstable, the corresponding alkoxysulfonium ions cycle to take place. can be generated by electrolysis in the presence of DMSO The use of non ─ conjugated dienes as substrates leads to (Scheme 25). 46 effective cyclization. For example, the reaction of 1 ─ phenyl ─ Bis ─ alkoxysulfonium ion pools can also be generated. 7 ─ methyl ─ 4,4 ─ dimethylocta ─ 1,6 ─ diene and ArSSAr with a Anodic oxidation of alkenes such as stilbene derivatives in the

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有機合成化学71-11＿06論文_Yoshida.indd 33 2013/10/21 14:52:16 Scheme 24. Further oxidation to the carbocation followed by reaction with DMSO gives the alkoxysulfonium ion. The present reaction integration serves as a good method for synthesizing pyrro- lidine and tetrahydrofuran derivatives. Anodic oxidation of 1,6 ─ dienes in the presence of DMSO leads to effective cyclization to give bis ─ alkoxysulfonium ion pools. Treatment with triethylamine then gives the corresponding cyclized diketones stereoselectively (Scheme 27 (2)). 6.2 Oxidative Hydroxylation via Alkoxysulfonium Ions Treatment of alkoxysulfonium ions with aqueous sodium hydroxide or methanol gives the corresponding alcohols via 57,58 O ─ S bond cleavage (Scheme 28). Oxidative hydroxylation 59 60 of the C ─ H bond and C ─ C double bond often suffers from Scheme 25. overoxidation, because the oxidation potentials of the alco- holic products are usually lower than those of the starting materials. On the other hand, the reaction integration using the “cation pool” method does not suffer from such a problem. For example, toluenes are oxidized to benzyl alcohols (Scheme 28 (1)). Alkenes are oxidized to 1,2 ─ diols via 1,2 ─ bis ─ alkoxysulfonium ions with high syn ─ selectivity (Scheme 28 (2)). Presum- presence of DMSO gives the corresponding 1,2 ─ bis ─ alkoxy- ably, the sulfonium ion moiety introduced rst directs the sulfonium ions, which are converted to 1,2 ─ diketones by treat- attack of the second DMSO, although the detailed mechanism ment with triethylamine (Scheme 26). Chemical oxidation of is not clear at present. Treatment of alkoxysulfonium ions stilbenes to benzils is known, but the method suffers from generated from alkenes bearing nucleophilic moieties such as 53 overoxidation to carboxylic acids with C ─ C bond cleavage. In tosylamides followed by reaction with OH - gives the corre- contrast, the integrated method does not suffer from such sponding alcohols with anti ─ selectivity (Scheme 28 (3)). One 18 problems because of the mild conditions of the product form- of the advantages of the present method is that the use of O ─ 18 61 ing step. DMSO leads to the formation of the O ─ labeled alcohols.

Scheme 26. Scheme 28.

The present integrated method can be combined with elec- trooxidative cyclization, and then serves as a useful method for constructing cyclic structures (Scheme 27). 54,55 For example, anodic oxidation of alkenes having a nucleophilic moiety in an appropriate position in the presence of DMSO gives cyclized alkoxysulfonium ion pools, which are converted to cyclized carbonyl compounds, on treatment with triethylamine (Scheme 27 (1)). 56 Electrochemical studies of the oxidation potentials involved indicate that the cation radical generated 7． Conclusions by one electron oxidation of the C ─ C double bond is attacked by the nucleophilic moiety to give the cyclized cation radicals. Both the “cation pool” method based on low temperature electrochemical oxidation, and the “cation ow” method based Scheme 27. on ow system chemistry have provided useful means for manipulating organic cations, which hitherto have been considered difcult to deal with in conventional reaction systems. The indirect “cation pool” method and the indirect “cation ow” system that are both based on chemical generation of organic cations using an electrochemically ─ generated reagent have also been developed. By means of these methods organic cations are generated in the absence of nucleophiles and are used for reactions with nucleophiles just like conventional reagents in organic synthesis. The successful applications of this methodology to carbocations and onium ions, which serve as powerful carbon electrophiles, and other organic cations

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有機合成化学71-11＿06論文_Yoshida.indd 34 2013/10/21 14:52:18 which serve as heteroatom electrophiles illustrate its potential Chem. 1998, 63, 5950. See also: (c) Chiba, K.; Uchiyama, R.; Kim, S.; in organic synthesis. Cation chain reactions and integrated Kitano, Y.; Tada, M. Org. Lett. 2001, 3, 1245. 26） Suzuki, S.; Matsumoto, K.; Kawamura, K.; Suga, S.; Yoshida, J. Org. electrochemical ─ chemical reactions based on the “cation pool” Lett. 2004, 6, 3755. method have opened up a new chapter in the chemistry of 27） Okajima, M.; Suga, S.; Itami, K.; Yoshida, J. J. Am. Chem. Soc. 2005, organic cations. These methods will hopefully enjoy a wide 127, 6930. 28） Saito, K.; Saigusa, Y.; Nokami, T.; Yoshida, J. Chem. Lett. 2011, 40, range of applications in the near future. 678. 29） Nokami, T.; Shibuya, A.; Tsuyama, H.; Suga, S.; Bowers, A. A.; References Crich, D.; Yoshida, J. J. Am. Chem. Soc. 2007, 129, 10922. 1） (a) Yoshida, J.; Suga, S. Chem. Eur. J. 2002, 8, 2651. 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有機合成化学71-11＿06論文_Yoshida.indd 35 2013/10/21 14:52:20 trochim. Acta 2003, 48, 1837. PROFILE 61） Fenselau, A. H.; Moffatt, J. G. J. Am. Chem. Soc. 1966, 88, 1762. Jun ichi Yoshida received his doctor’s degree at K─yoto University under the supervision of Prof. Makoto Kumada in 1981. In 1979 Yoshida joined the faculty at Kyoto Institute of Technology as an assistant professor. In the meantime, he visited University of Wis- consin during 1982 ─ 1983, where he joined the research group of Prof. B. M. Trost. In 1985 he moved to Osaka City University, where he was promoted to an associate professor in 1992. In 1994 he was appointed as a full professor of Kyoto Univ. His research interests include integrated organic synthesis on the basis of reactive intermediates, organic electron transfer reactions, organometallic reactions, and ow microreactor synthesis. Awards: the Progress Award of Synthetic Or- ganic Chemistry, Japan (1987), the Chemical Society of Japan Award for Creative Work (2001), Nagoya Silver Medal (2006), Hum- boldt Research Award (2007), Green and Sustainable Chemistry Award (2010), and Dogane Award (2010), The Chemical Society of Japan (CSJ) Award (2013).

Yosuke Ashikari graduated from Kyoto Uni- versity in 2008. He received his M.Sc. in 2010 from Kyoto University under the supervision of Professor Jun─ ichi Yoshida. Cur- rently, he is working on his Ph.D. thesis on the integration of electrochemical oxidation and chemical reactions. Awards: the Student Poster Award of the Electro Organic Chem- stry Symposium (2008), the CSJ Student Presentation Award 2013 (2013).

Kouichi Matsumoto graduated from Kyoto University in 2005. He received his Ph.D. in 2010 from Kyoto University under the supervision of Professor Jun ─ ichi Yoshida. In 2010, he joined the group of Prof. Shigenori Kashimura at Kinki University as an Assis- tant Professor. His current research interest is electro ─ organic chemistry. Awards: the CSJ Student Presentation Award 2009 (2009), and Prize of the Promotion of Engineering Re- search in Foundation for the Promotion of Engineering Research (2012).

Toshiki Nokami received his Ph.D. from Kyoto University in 2004 under the supervision of Professor Jun ─ ichi Yoshida. Then he spent a year in ETH Zurich as a post doctoral fellow under the direction of Professor Peter H. Seeberger. Since 2005 he had been a faculty of the Department of Synthetic Chemi- stry and Biological Chemistry of Kyoto Uni- versity. In 2012, he moved to the Department of Chemistry and Biotechnology of Tottori University as an Associate Professor. His research interests include synthetic organic chemistry, carbohydrate chemistry, and organic electrochemistry. Awards: Meiji Seika Kaisha, Ltd. Awards in Synthetic Organic Chemistry, Japan (2008), The Progress Awards of Organic Electrochemistry (2009), The 26th Young Scholar Lecturer of the Chemical Society of Japan (2012), and The 15th Incentive Awards of the Japanese Soci- ety of Carbohydrate Research (2012).

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