Activation of Manganese Metal with a Catalytic Amount of Lead and Me3sicl and Its Application to Organic Synthesis

Activation of Manganese Metal with a Catalytic Amount of Lead and Me3SiCl and Its Application to Organic Synthesis

Kazuhiko Takai Department of Applied Chemistry, Faculty of Engineering, Okayama University,

ReceivedJune 5, 2002

Abstract : The reducing ability of manganese metal can be utilized effectively by treatment with a catalytic amount of PbCl2 and Me3SiCl. This article discusses the following specific themes using the activated manganese metal as a reductant. 1) Generation of alkyl radicals and their trapping with a, a-unsaturated esters. 2) Three-component coupling reactions of alkyl iodides, electron-deficient olefins, and carbonyl compounds based on the concept of sequential generation of a radical and anionic species. 3) Sequential 1,4-addition. and Claisen rearrangement. 4) Generation of non-stabilized carbonyl ylides. 5) Selective reduction of iodoform and its application to the synthesis of alkenylsilanes.

and O(1s) peaks were observed (Figure 1).6 When the man- 1. Introduction ganese powder (A) was subjected to spattering for 14 min On the floor of deep oceans, manganese nodules deposit (B), broadening of two Mn peaks, Mn(2p1/2) and Mn(2p3/2), with associated metals, such as copper, nickel, and cobalt. was observed. However, it is difficult to distinguish between The Clarke number, i.e., weight % at the crust of the earth, of Mn-Mn and Mn-O peaks presumably due to a small differ- manganese is smaller than that of zinc, and thus, is a relative- ence in binding energy. Thus, the content of manganese oxide ly abundant metal. Manganese is slightly more expensive can be estimated by the atom ratio O / Mn, and the ratio was than zinc. Manganese metal (Mn(II)/Mn(0), E0 = -1.185 V) decreased by the spattering. has stronger reduction potential than zinc (Zn(II)/Zn(0), E0 From studies on activation of zinc metal, it was recognized = -0 .762 V); however, it has rarely been utilized in organic that the metal-oxide coating is effectively removed by treat- synthesis except in a few cases.1-5This is because it is difficult ment with Me3SiCl and that electron transfer from zinc to to fully utilize the reducing ability of the manganese metal, organic substrates proceeds smoothly.7 Thus, the manganese except in the case of Rieke's manganese.2 For example, allyl metal was treated with Me3SiCl (10 mol% of Mn) in THE at bromide is easily reduced with zinc; however, it is not easily 25 t for 1 h, and a decrease of the atom ratio 0 / Mn (C) reduced with commercial manganese powder without any was observed. The result suggests abstraction of oxygen activation. Two precedent examples by Hiyama and Cahiez atoms from the surface. The effect of the treatment with revealed that pre-treatment of the manganese metal with Me3SiCl corresponded to a 10-min spattering, i.e., ca. 100 iodine or zinc chloride-allyl bromide is indispensable for the nm depth. 1H NMR analysis of a supernatant solution of the Barbie-type allylation of benzaldehyde (Scheme 1).' mixture of manganese powder and Me3SiCl in THF-d8 after stirring at 25 t for 1 h under an argon atmosphere, showed Scheme 1 a peak of Me3SiOSiMe3. The observation, therefore, also supports the abstraction of oxygen atoms from the surface by treatment with Me3SiCl.

One reason for the low reactivity of the manganese metal toward organic compounds is a thin but tightly bound oxide layer on its surface. This disturbs the electron-transfer from the metal to the organic substrates. Starting with the development of a novel activation method to remove the oxide layer, we began research on the utilization of manganese in organic synthesis. Figure 1. Measured Mn(2p) and O(1s) X-ray photoelectron spectra 2. Activation of Manganese Metal of Mn powder. Commercial manganese powder (A) was examined by X-ray photoelectron spectroscopy (XPS), and the Mn(2p)

Vol.60 No.11 2002 ( 25 ) 1055 In order to accelerate the electron transfer from the metal radicals by reduction of alkyl halides (R-X) with reducing to the organic compound, several methods such as the Rieke agents; however, the method is not so popular as further activation method have been reported.2b Another method for reduction of the initial radicals (R.) leading to alkyl anions the acceleration of electron transfer is to add a catalytic (R-) normally proceeds faster than the first radical formation amount of a second metal element to the target metal. This under the reduction conditions. Although intramolecular rad- sometimes has the advantage of activating the target metal ical cyclization before anionic reactions has been observed in under mild conditions.8 Activation of manganese metal was several cases,1° there are few examples of the intermolecular explored using Barbier-type allylation of cyclododecanone version due to the above restriction. Two requirements exist (1) with allyl bromide as a probe (Scheme 2). Therefore, we for a suitable reducing agent to connect the two reactions: (1) examined several additives together with Me3SiCl, and found The initial radial (R.) is not easily reduced to R.- and has a that addition of a catalytic amount of PbCl2 accelerates the sufficient lifetime to undergo an intermolecular reaction. (2) allylation markedly. This effect of lead on manganese is The final radical (R' .)is easily subjected by one-electron opposite to that on zinc where a catalytic amount of lead reduction to R'- Therefore, the desired reductant should be deactivates the metal.7c When 0.2 equiv. of PbC12 was added weak enough to be able to discriminate between the two radi- to the reaction mixture, an exothermic reaction (ca. 40 r) cals R. and R'.. With these considerations in mind, a man- was observed and allylation of 1 was completed at 25 r ganese-lead reducing agent was utilized, and the above con- within 30 min to give homoallylic alcohol 2 in 92% yield. The cept was realized as three-component coupling reactions. amount of PbCl2 can be reduced to 0.25 mol% of manganese 3.1 Three-Component Addition of Iodoalkanes, powder without any decrease of the yields, but the allylation Electron-Deficient Olefins, and Carbonyl Corn- did not proceed without addition of Me3SiCl. Manganese pounds11 metal can reduce Pb(II) to Pb(0), however, allylation of 1 When the tertiary iodoalkane 3 was treated with man- using lead powder and Me3SiCl did not proceed at all. Thus, ganese metal in the presence of PbC12 and Me3SiC1 in THF, we assume that the allylation is not promoted with activated reduction of 3 proceeded smoothly, and olefin derived by Pb(0).8b Because there was no obvious difference in the XPS dehydroiodination, hydrocarbon and a dimeric coupling spectra between the presence and the absence of PbC12 (Fig- product were obtained (Scheme 4).11 ufe 1, (C) and (D)), the effect of the catalytic amount of PbC12 is still obscure. Scheme 4

Scheme 2

The iesult suggests that treatment of the iodoalkane with the activated manganese generates an alkyl radical. Thus, 1,4-addition of the radical to an a, f3-unsaturated ester under protic conditions was examined, and it was found that the addition proceeded in a high yield (Scheme 5). 3. Sequential Generation of Radical and Anionic Species

Carbanion and radical chemistry represent integral parts Scheme 5 of organic synthesis. However, the reactivities of the two intermediates are sometimes complementary, and so sequential utilization of the two offers an untapped potential for building more complex molecules (Scheme 3).9

Scheme 3 Organocopper reagents add to a,/3-unsaturated carbonyl compounds in a 1,4-fashion. However, it is not easy to trap the intermediate copper enolate with electrophiles.12 In 1978, Nishiguchi and Shono reported zinc-mediated three-component addition of iodoalkanes, electron-deficient olefins, and carbonyl compounds.13 Although the reaction mechanism has not yet been clarified, the first step could be the 1, 4-addition of alkyl radicals. Therefore, we applied the manganese-mediated radical generation from iodoalkanes in the presence of Alkyl radicals are usually prepared either by chain meth- carbonyl compounds under aprotic conditions, and found ods, homolytic cleavage of covalent bonds, or by nonchain that the expected three-component addition reactions pro- methods based on redox reactions. One of the latter accesses ceeded (Scheme 6)."

1056 ( 26 ) J. Synth. Org. Chem., Jpn. Scheme 6 Scheme 8

The three-component coupling of alkyl iodides, activated olefins, and carbonyl compounds proceeded with primary, Scheme 9 secondary and tertiary alkyl iodides (Scheme 7), but in the case of primary iodide, 5 mol% of PbC12 was necessary to accelerate the process. Both acrylonitrile and acrylic esters could be employed as activated olefins, while the reaction with an alkyl vinyl ketone gave a complex mixture. A substituent at the $-position of the electron-deficient olefin decreased the reactivity of the olefin, and the reaction also required 5 mol% of PbC12. Ketones and aldehydes could be used as the third component, and the diastereoselectivity of the anionic addition was approximately 1:1-2:1 ratio.

Scheme 7 electron-withdrawing group proceeds faster than addition to a different unsaturated bond. Sequential generation and utilization of a radical and anionic species, therefore, are the essential factors in the coupling reaction of iodoalkanes, a,P-unsaturated nitriles (or esters), and ketones (or aldehydes), and the protocol itself can provide a new access to similar coupling products that are difficult to obtain with organocuprates in one-pot reactions due to their complex nature.

Scheme 10

In order to clarify the mechanism of the three-component coupling reaction, the following reactions were conducted. Similar three-component coupling reactions occurred

When 7-iodo-2-methyl-2-heptene (4) was used as an alkyl when ethyl propiolate was used as the electron-deficient iodide, intramolecular radical cyclization (5 •¨ 6) occurred olefin (Scheme 11).14 A catalytic amount of PbCl2 was also before intermolecular addition of 5 to acrylonitrile (Scheme necessary to promote the reactions with propiolate similarly

8). A three-component coupling product without the cycliza- to those with acrylates, and in this case, addition of Et2A1C1 tion, however, was not detected. instead of Me3SiCl and an acetonitrile solvent gave better

Hydroxynitrile 8 was obtained in 50% yield in the case of yields. Only Z stereoisomers were obtained by the reactions 4-iodo-1-butene (7) (Scheme 9), although no coupling prod- using t-butyl iodide. When isopropyl iodide was used as an uct was obtained from further cyclization. The result suggests alkyl iodide, the reaction proceeded slowly and the yield of that the second one-electron reduction of radical 9 to a 11 decreased to 20% after 12 h stirring at 25 °C. The reaction nitrile anion 10 proceeds very quickly. rate was enhanced by increasing the amounts of both

Consequently, the three-component coupling is realized by Et2A1C1 (0.1•¨0.5 equiv.) and PbCl2 (0.06 •¨ 1.0 equiv.), a subtle balance of the reaction rates (Scheme 10). The obtaining the adduct 11 in 85% yield. The internal trap of reduction rate of an alkyl radical to an alkyl anion is slower the formed manganese allenoate occurred with 3-oxo butyl than 1, 4-addition of the radical to an activated olefin. How- propiolate to give 12. ever, one-electron transfer to the resulting radical having an

Vol.60 No.11 2002 ( 27 ) 1057 Scheme 11 Scheme 13

stituent at the ƒÀ-position of a, J3-unsaturated ester retards the

reaction considerably, which is usually observed in 1, 4-addi-

tion mediated by an alkyl radical. In contrast to the

The stereoselectivity of this coupling reaction can be Simmons-Smith reaction, 2-methyl-5-phenyl-2-pentene, the explained as follows (Scheme 12). An alkyl radical produced simple trisubstituted olefin, was recovered almost quantita- by the reduction of an alkyl iodide with activated manganese, tively under the standard conditions. adds to ethyl propiolate to give radical 13. One-electron reduction of the formed radical 13 affords the allenoate 14. Scheme 14 Aldol-type addition of the formed allenoate occurs at the C-2 position of 14, and it must occur in the plane of the groups attached to the C-3 and thus, proceeds preferentially from the less hindered side of the allenoate 14, i.e., the opposite side of the t-butyl group. Therefore, 2-(1-hydroxyalkyl)- 2-alkenoate with Z-configuration is produced in a stereoselective manner. Trapping of the radical 13 with I. or H-produces a mixture of both (Z)- and (L)-2-alkenoates, showing a sharp contrast to this anionic process.15

Scheme 12

A possible mechanism for the cyclopropanation is shown in Scheme 15. Because of the mild reducing power of manganese metal, further reduction of chloromethyl radical 18 to its anion is slower than 1, 4-addition of the radical to an electron-deficient olefin. In contrast, the second one-electron reduction of 19 proceeds smoothly due to the electron-with- 3.2 Cyclopropanation of Electron-Deficient Olefins16 drawing group. Simmons-Smith reaction, the carbenoid approach, is usually employed for cyclopropanation of olefinic double bonds; Scheme 15 however, the reaction with electron-deficient olefins proceeds slowly and, sometimes, results in recovery of the olefins.'? Another pathway to cyclopropanation of electron-deficient olefins is a stepwise addition-substitution approach.18 We employed the manganese-generated alkyl radical for the first 1,4-addition step of the stepwise cyclopropanation. As a methylene radical-cation synthon, chloroiodomethane was employed (Scheme 13). Treatment of 3-phenylpropy- lacrylate (15) with chloroiodomethane, manganese, PbCl2 and Me3SiCl in THE for 20 min produced the desired cyclo- propanecarboxylic ester 16 in 62% yield along with y-chlorobutanoate 17, the 1,4-adduct in 16%. The yield of 4. Sequential 1,4-Addition and Claisen Rearrangement2° the ester 16 was improved by addition of 0.15 equiv. of DMAP as an activator of Me3SiC1.19Reactions with diiodo-, Ireland-Claisen rearrangement is a useful transformation dibromo- and dichloromethane did not proceed (< 3% yield), from allylic esters to (E)-y,6-unsaturated carboxylic acid in a and 15 was recovered in almost quantitative yields. stereoselective manner. Ketene silyl acetals of allylic esters are The cyclopropanation with chloroiodomethane and acti- the precursors of the rearrangement3 and are usually pre- vated manganese also proceeds with an a,/3-unsaturated pared by deprotonation and trapping with Me3SiCl. A ketone and an amide (Scheme 14). It is worth noting that the 1,4-addition to allylic acrylates and silylation can also be protocol can also be applied to a vinyl sulfone with which the used;4 , 5 however, as the acrylates have four potential elec- Simmons-Smith reaction does not work well.17 The sub- trophilic sites which can result in 1,2-addition (a), 1,4-addi-

1058 ( 28 ) J. Synth . Org . Chem ., Jpn .

tion (b), SN2 (c), and SN2' (d) positions (Figure 2), it is nec- are produced in almost 1 / 1 ratio under the conditions. In essary to control the regiochemistry. contrast to the reported Ireland-Claisen rearrangement, a substituent at the y position did not accelerate the rearrangement. Treatment of propargylic acrylate with isopropyl iodide and the manganese system at 40 t for 1 h produced the cor- responding allenic carboxylic acid 24 in 86% yield as a 1 / 1 mixture of diastereomers.

Figure 2 Scheme 17

Alkyllithium and magnesium reagents selectively add to the carbonyl carbon in a 1,2-fashion, while dialkylcopper lithium reagents react exclusively at the SN2'position.21 We employed the manganese-generated alkyl radical to the selective 1, 4-addition to the allylic acrylate leading to the ketene silyl acetal, and found that the successive Ireland-Claisen rearrangement from the intermediate silyl acetals proceeded smoothly at ambient temperature. Treatment of acrylate 20 with isopropyl iodide and manganese activated by a catalytic amount of PbC12 and Me3SiC1 in a mixed solvent of DMF and THE at 90 r for 3 h, afford- ed 1,4-adduct 21 in 47% yield (Scheme 16). When 3 equiv. of Me3SiCl was used with the substrate, the adduct 21 and rear- ranged product 22 were produced in 43% and 31% yields, respectively, at 25 t for 30 min. This result suggests that the rearrangement does not proceed from a manganese enolate anion but, rather, occurs after trapping to its silyl acetal. It is A plausible mechanism for this sequential reaction is known that 4-(dimethylamino)pyridine (DMAP) and shown in Scheme 18. The reduction of an iodoalkane with N-methylimidazole (NMI) accelerate the silylation step,19 and the manganese-PbCl2-Me3SiCl system produces the corre- thus when added, the sequential Claisen rearrangement pro- sponding alkyl radical 25, which has sufficient lifetime for ceeded smoothly, and the acid 22 was obtained in excellent intermolecular addition to an acrylate, even under the reduc- yields. The double bond produced was proven to have E tion conditions. In contrast, reduction of the adduct radical geometry as expected from the Ireland-Claisen rearrange- 26 takes place smoothly to give an ester enolate 27 which is ment. trapped with Me3SiCl with the assistance of NMI. The Ire- land-Claisen rearrangement and hydrolysis affords an Scheme 16 (E)-7,(5-unsaturated acid.

Scheme 18

Primary, secondary and tertiary alkyl iodides can be used for the sequential 1,4-addition and Ireland-Claisen rearrangement (Scheme 17). Because the reduction of a primary iodide proceeds slower than that of a secondary iodide, in this case, the reaction was conducted with 5 mol% of PbCl2 and heated at 40 C. Although 1, 4-addition occurred smoothly with t-butyl iodide in almost quantitative yield, the successive rearrangement proceeded slowly, probably due to 5. Generation of Non-Stabilized Carbonyl Ylides22 steric hindrance around the newly formed carbon-carbon bond. The product 23 was obtained as an anti I syn mixture When a solution of 1-iodoethyl trimethylsilyl ether (28), of diastereomers in a 48 / 52 ratio. The low diastereoselectivi- derived from acetaldehyde and Me3SiI in dichloromethane at ty stems from the fact that both E and Z ketene silyl acetals 25 •Ž, was added to a mixture of methyl acrylate, manganese,

Vol.60 No.11 2002 ( 29 ) 1059

and a catalytic amount of PbC12 and Me3SiCl in THF and 1-dodecene (35), the [3 + 2] cycloaddition products 36 and 37 DMF, the expected 1,4-addition product of the a-triethyl- of both olefins were obtained in 94% and 80% yields, respec- siloxy radical 29 to the acrylate was not obtained, and tively. In contrast, the cycloaddition product 36 was pro- instead, a diastereomeric mixture of substituted tetrahydrofu- duced with 34 in 89% yield, and 35 was recovered in 90% rans 30 was produced in 85% combined yield (Scheme 19).22 yield when 1 equiv. of 33 was generated (Scheme 21). Because of the similar reactivity of carbonyl ylides from the bis(1-iodoalkyl) ether 32 and 1-iodoalkyl triethylsilyl ether Scheme 21 31, we are tempted to assume that the nonstabilized carbonyl ylide 33 is generated by manganese reduction of 32 that is in equilibrium with the 1-iodoalkyl triethylsilyl ether 31.22,23In the reaction between 28 and the methyl acrylate, the [3 + 2] cycloaddition proceeded without the addition of PbC12, and the diastereomeric ratios of products between the acrylate and the nonstabilized carbonyl ylide 33 depended on the presence of PbC12.

Scheme 19

6. Preparation of Diiodomethyltrimethylsilane25 There are several exceptions of redox reactions which can- not be explained from only the table of standard reduction/oxidation potentials. For example, when iodoform is treated with SmI2 (Sm(III)/Sm(II), E0 = -1.55 V) in THF, one of the iodine atoms is reduced to give a samarium carbenoid I2CHSmI2 which reacts with an aldehyde.26 Reduction of iodoform with zinc (Zn(II)/Zn(0), E0 = -0.762 V) proceeds much slower than that with SmI2.27In contrast, reduction of iodoform with chromium(II) (Cr(III)/Cr(II), E0 = －0 .407 V) generates a geminal dichromium species, and the Cycloaddition reactions with carbonyl ylides are one of the chromium species reacts with an aldehyde to give an most valuable methods to construct highly substituted oxy- (E)-iodoalkene with one-carbon extension.28 We have found gen heterocycles. Besides stabilized carbonyl ylides developed that treatment of iodoform with manganese (Mn(II)/Mn(0), by Padwa, Hosomi and Hojo generated nonstabilized ylides E° = -1.185 V) in THE in the presence of an excess amount by treatment of 1-iodoalkyl triethylsilyl ethers with Sm12.24 of Me3SiC1 affords Me3SiCHI9 (38) in 33% yield (Scheme In contrast to SmI2, the manganese system does not reduce 22).25The yield of 38 improved to 59%, when DME was used an a,$-unsaturated carbonyl compound or promote pinacol as a solvent and NaI was added. One of the three iodine coupling of an aldehyde; therefore, [3 + 2] cycloaddition with atoms is reduced with manganese and selectively replaced an a,/3-unsaturated ketone or ester proceeded without the with a trimethylsilyl group. Reduction of iodoform did not formation of undesirable byproducts (Scheme 20). occur without addition of Me3SiCl; however, PbC12 was not necessary for the reaction. Chlorotrimethylsilane acts as an Scheme 20 activating agent for manganese metal as well as a trapping agent of the manganese carbenoid. To our surprise, much easily reduced Me3SiCHI2 remained unchanged in the reaction mixture.

Scheme 22

7. Utilization as a Reductant for a Chromium(III) In 1996, Fiirstner reported that manganese could be used as a reductant for chromium(II)-mediated reactions (Scheme Chemoselectivity in the [3 + 2] cycloaddition between an 23).4a Although manganese(0) is a stronger reductant than a,13-unsaturated ester and a simple olefin was observed. For chromium(II), it does not reduce allyl bromide without addi- example, when 4 equiv. of 33 was generated from the tion of a catalytic amount of lead (vide supra). This feature bis(1-iodoethyl) ether (32), manganese, and a catalytic enables the construction of a catalytic cycle of chromium amount of PbC12 in the presence of the acrylate 34 and with manganese(0), and several chromium(II)-catalyzed reac-

1060 ( 30 ) J. Synth . Org . Chem ., Jpn . Scheme 23 Scheme 25

been utilized in organic synthesis due to the lack of an appropriate activation method. We have found that man- tions were realized.4 ganese metal is activated with a catalytic amount of Me3SiCl A typical reaction using chromium(II) is iodoolefination of and PbCl2, and that treatment of an iodoalkane with the an aldehyde with a gem-dichromium species derived by activated manganese generates a radical and anionic species reduction of iodoform with CrCl2.28 The protocol provides sequentially. Utilizing this concept of sequential generation, (E)-iodoalkenes from aldehydes with one-carbon extension we have realized a three-component coupling reaction and a under mild conditions in chemo- and stereoselective man- sequential 1,4-addition-Claisen rearrangement. The activat- ners. This transformation, however, requires 6-8 equiv. of the ed manganese metal has been used to generate non-stabilized one-electron reductant, CrCl2, to obtain reasonable yields. carbonyl ylides under mild conditions. Also, an application Because reduction of iodoform with zinc proceeded quite of the manganese-PbCl2 reagent for 1, 2-elimination in sugar slowly, the amount of chromium(II) can be reduced using systems appeared recently.29Without addition of PbCl2, man- zinc as a reductant.27 During the research, one-pot formation ganese metal is not so reactive but can reduce chromium(III) of an (E)-alkenylsilane from an aldehyde was discovered by and titanium(IV). Therefore, manganese is often used as a chance (Scheme 24).25 reductant for catalytic cycles of chromium and titanium species in recent years.4,5 Scheme 24 In order to accomplish selective organic transformations by using the reducing ability of metals, it is important to optimize the electron transfer process from the metals to the organic substrates. Therefore, manganese, which has moder- ate reducing ability, could be one of the metals of choice. It is hoped this manuscript will lead to further use of manganese metal.

References 1) (a) Hiyama, T.; Sawahata, M.; Obayashi, M. Chem.Lett. 1983, 1237;Nippon Kagakukaishi 1984, 1022.(b) Cahiez, G.; Chavant, Two important faetois for the preferential formation of an P. Y. TetrahedronLett. 1989,30, 7373. 2) Highly activated Mn powder was prepared by reduction of alkenylsilane over an iodoalkene are shown to be (1) a cat- manganese salts with lithium naphthalenide. (a) Kim, S. H.; alytic amount of CrCl2, and (2) a mixture of iodoform, Hanson, M. V.; Rieke, R. D. TetrahedronLett. 1996,37, 2197; Me3SiCl, manganese, and CrCl2, which is stirred for 5 min Rieke, R. D.; Kim, S.-H. J. Org. Chem.1998, 63, 5235; Rieke, R. D. AldrichimicaActa 2000,33, 52. before addition of an aldehyde. Selective reduction of iod- 3) For reduction of a manganese(II) salt with C8K,see: Fiirstner, oform followed by silylation occurred with manganese and A.; Brunner,H TetrahedronLett. 1996,37, 7009. Me3SiCl in the reaction mixture (Scheme 25). Because a cat- 4) (a) Fiirstner, A.; Shi, N. J. Am. Chem. Soc. 1996, 118, 2533; alytic amount of chromium(II) was used, reduction of iod- 12349. (b) Boeckman, R. K., Jr.; Hudack, R. A., Jr. J. Org. Chem.1998, 63, 3524. (c) Savatog, A.; Boland, W. Synlett 1998, oform with a stoichiometric amount of manganese was pre- 549. (d) Bandini, M.; Cozzi, P.C.; Melchiorre, P.; Umani- ferred to that with CrCl2 leading to a gem-dichromium Ronchi, A. Angew.Chem., Int. Ed. 1999,38, 3357. (e) Hari, A.; species, ICH(CrX2)2. The (E)-alkenylsilanes was produced Karan, C.; Rodrigues,W. C.; Miller, B. L. J. Org. Chem.2001, 66, 991. with the gem-dichromium species Me3SiCH(CrX2)2 generated 5) (a) Mn-Ti: Green, M. L. H.; Lucas, C. R. J. Chem.Soc., Dalton from Me3SiCHI2 and CrCl2. Trans. 1972,1000; Coutts, R. S. P.; Wailes,P. C.;Martin, R. L. J. Organomet.Chem. 1973, 47, 375; Sekutowski,D.; Jungst, R.; 8. Conclusion Stucky, G. D. Inorg. Chem. 1978, 17, 1848; Stephan, D. W. Organometallics1992, 11, 996. (b) Gansaiier, A.; Bauer, D. J. From the table of standard oxidation/reduction potentials, Org. Chem.1998, 63, 2070; Gansaiier, A.; Pierobon, M.; Bluhm, the potential for using manganese metal as a reductant seems H. Angew.Chem., Int. Ed. 1998, 37, 101. (c) Dunlap, M. S.; to be almost the same as that of zinc. However, it has rarely Nicholas, K. M. Synth.Commun. 1999, 27, 1097. (d) Parrish, J.

Vol.60 No.11 2002 ( 31 ) 1061 D.; Little, R. D. Org. Lett. 2002, 4, 1439. (e) Mn-Cu: Li, C-J.; 20) Takai, K.; Ueda, T.; Kaihara, H.; Sunami, Y; Moriwake, T. J. Meng, Y; Yi, X.-H.; Ma, J.; Chan, T. H. J. Org. Chem. 1998, Org. Chem. 1996, 61, 8728. 63, 7498. 21) Aoki, Y; Kuwajima, I. TetrahedronLett. 1990, 31, 7457. 6) Takai, K.; Ueda, T.; Hayashi, T.; Moriwake, T. Tetrahedron 22) Takai, K.; Kaihara, H.; Higashiura, K.-i. Ikeda, N. J. Org. Lett. 1996, 37, 7049. Chem. 1997, 62, 8612. 7) (a) Gaudemar, M. Bull. Soc. Chim. Fr. 1962, 974. (b) Knochel, 23) Hojo, M.; Aihara, H.; Suginohara, Y; Sakata, K.; Nakamura, P.; Yeh, M. C. P.; Berk, S. C.; Talbert, J. J. Org. Chem. 1988, 53, S.; Murakami, C.; Hosomi, A. J. Org. Chem. 1997, 62, 8610. 2390. (c) Takai, K.; Kakiuchi, T.; Utimoto, K. J. Org. Chem. 24) Hojo, M.; Aihara, H.; Hosomi, A. J. Am. Chem. Soc. 1996, 118, 1994, 59, 2671. 3533. 8) (a) Takai, K.; Ikawa, Y. Org. Lett. 2002, 4, 1727. (b) Tanaka, 25) Takai, K.; Hikasa, S.; Ichiguchi, T.; Sumino, N. Synlett 1999, H.; Yamashita, S.; Ikemoto, Y; Torii, S. Chem. Lett. 1987, 673. 1769. 9) Wender, P. A. (Ed.) Chem. Rev. 1996, 96 (1&2) "Frontiers in 26) ConcellOn, J. M.; Bernad, P. L.; Perez-Andres, J. A. Tetrahedron Organic Synthesis." Lett. 1998, 39, 1409. 10) For some representative examples, see: (a) Cr: Takai, K.; Nitta, 27) Takai, K.; Ichiguchi, T.; Hikasa, S. Synlett 1999, 1268. K.; Fujimura, O.; Utimoto, K. J. Org. Chem. 1989, 54, 4732. 28) Takai, K.; Nitta, K.; Utimoto, K. J. Am. Chem. Soc., 1986, 108, (b) Sm: Molander, G. A.; Kenny, C. J. Org. Chem. 1991, 56, 7408 1439. Molander, G. A.; McKie, J. A. J. Org. Chem. 1995, 60, 29) Tanaka, K.; Yamano, S.; Mitsunobu, 0. Synlett 2001, 1620. 872; Curran, D. P.; Totleben, M. J. J. Am. Chem. Soc. 1992, 114, 6050; Curran, D. P.; Fevig, T. L.; Jasperse, C. P.; Totleben, M. J. Synlett 1992, 943; Molander, G. A.; Harris, C. R. Chem. Rev. 1996, 96, 307. (c) Zn: Bronk, B. S.; Lippard, S. J.; Danheiser, R. PROFILE L. Organometallics 1993, 12, 3340. 11) Takai, K.; Ueda, T.; Ikeda, N.; Moriwake, T. J. Org. Chem. 1996, 61, 7990. Kazuhiko Takai is a professor of the 12) Suzuki, M.; Kawagishi, T.; Suzuki, T.; Noyori, R. Tetrahedron Department of Applied Chemistry, Lett. 1982, 23, 4057. Okayama University. He was born in 13) Shono, T.; Nishiguchi, I.; Sasaki, M. J. Am. Chem. Soc. 1978, Tokyo in 1954. He received his B.A. in 100, 4314. 1977 and Ph.D. in 1983 from Kyoto 14) Kaihara, H.; Ueda, T.; Takai, K.; Moriwake, T. 70th Annual University under the direction of Profes- Meeting of the Chemical Society of Japan, 3J136 (1996). sor Hitosi Nozaki. In 1981, he was 15) (a) Giese, B.; Lachhein, S. Angew. Chem., Mt. Ed. Engl. 1982, 21, appointed as an assistant professor of 768. (b) Curran, D. P.; Kim, D. Tetrahedron1991, 47, 6171; Cur- Dr. Nozaki's group at Kyoto University. ran, D. P.; Kim, D.; Ziegler, C. Tetrahedron 1991, 47, 6189. (c) During that time he joined Professor C. Lowinger, T. B.; Weiler, L. J. Org. Chem. 1992, 57, 6099. H. Heathcock's group at the University 16) Ueda, T.; Ishiyama, T.; Takai, K.; Moriwake, T. 70th Annual of California, Berkeley for one year Meeting of the Chemical Society of Japan, 3PB104 (1996). from 1983 as a postdoctral fellow. In 17) (a) Wittig, G.; Wingler, F. Liebigs Ann. Chem. 1962, 656, 18; 1994, he moved to Okayama University Chem. Ber. 1964, 97, 2139; 2146. (b) Wittig, G.; Jautelat, M. as an associate professor, and became a Liebigs Ann. Chem. 1967, 702, 24. (c) Denis, J. M.; Girard, C.; full professor in 1998. He received the Conia, J. M. Synthesis 1972, 549. Chemical Society of Japan Young 18) (a) Corey, E. J.; Chaykovsky, M. J. Am. Chem. Soc. 1964, 81, Chemists Award in 1989. His research 1640. (b) Corey, E. J.; Jautelat, M. J. Am. Chem. Soc. 1967, 89, interest is in the development of selec- 3912. (c) Corey, E. J.; Chaykovsky, M. J. Am. Chem. Soc. 1965, tive synthetic reactions with novel 87, 1353. (d) Truce, W. E.; Badiger, V. V. J. Org. Chem. 1964, 29, organometallic species. 3277. 19) Bassindale, A. R.; Stout, T. TetrahedronLett. 1985, 26, 3403.

1062 ( 32 ) J. Synth. Org. Chem., Jpn.