Development of Allyl-Transfer Reaction and Its New Aspect

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To date, there have been no reported methods for effectively synthesizing homoallylic alcohols (2,RCH(OH)CH_2CH=CHR^3) via alk-2-enylation of aldehydes (RCHO). On the other hand, we recently discovered the first convenient and highly stereoselective but-2-enylation of aldehydes (RCHO) to give (RC^*H(OH)CH_2CH=CHCH_3) by allyl-transfer reaction, in which γ-adduct of homoallylic alcohol (1,R^1R^2C^*(OH)C^*HR^3CH=CH_2) surved as an allyl donor and its allylic functionality (R^3CH=CHCH_2) was transfered to aldehyde due to [3.3]-sigmatropic rearrangement via the most stable 6-membered chair-like cyclic transition state of the oxocarbenium ion intermediate (RCH=O^+C^*R^1R^2C^*HR^3CH=CH_2; R^3=CH_3) derived from hemiacetal (RCH(OH)OC^*R^1R^2C^*HR^3CH=CH^2) of aldehyde and 1. Further, we demontrated the possibility of alk-2-enylation of aldehydes via an allyl-transfer reaction using optically active menthones ((-)-,(+)-, and (+)-iso) as chiral auxiliaries. We also discovered that this improved the yield of the product due to an icrease in the steric valk of the alkyl chains. Highly optically acitive 2,3,4,6-tetrasubstituted tetrahydropyrans were prepared in good yield by Prins cyclization reaction of 2 and aldehydes.More recently, we discovered an asymmetric 4-benzyloxybut-2-enylation of aldehydes to give α-adduct of homoallylic alcohols (RC^*H(OH)CH_2CH=CHCH_2OBn), in which we successfully prepared the necessary homoallylic alcohol (R^4C^*H(HO)C^*HR^3CH=CH^2; R^3=CH_2OBn) without using organometallic compounds such as R^3CH=CHCH_2M (M=metal) which is impossible to prepare because of its intability (when R^3=CYR_2;Y=OBn, halogens).We discovered "Allyl-Transfer reaction" which gave highly optically active and a variety of fuctionalyzed α-adduct of homoallylic alcohols, conveniently.