Efficient Methods for Asymmetric Synthesis Based on Asymmetric Transmission via Sigmatropic Rearrangements

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The main results of this 2-year project are as follows :Theme (1)"The Mechanism of the Asymmetric Transmission via [2,3]-Wittig Rearrangement" : A series of experiments using chiral carbanion termini generated from optically active tin compounds provided pieces of evidence in support of the "dynamic kinetic resolution mechanism" for the asymmetric transmission concerned.Theme (2)"Asymmetric Transmission via the [1,4]-Wittig Rearrangement" : First, the carbanion rearrangement of allyl endo-and exo-bornyl ether was found to predominantly undergo the rarely precedented [1,4]-Wittig rearrangement which proceeds in non-stereospecific manner. Second, similar (but at lower temperatures) rearrangements of allyl cis-carvenyl ether and allyl trans-piperityl ether were shown to undergo the [1,4]-Wittig rearrangement predominantly which proceeds with complete retention of configuration. Interestingly enough, the rearrangement of -allyl cis-piperityl ether was found to undergo the [2,3]-Wittig rearrangement exclusively. Thus, the substrate conformation has been revealed to play a key role in determining the periselectivity in these carbanion rearrangements. Third, three convenient procedures have been developed for effecting the [1,4]-retero-Brook rearrangement of allyl silyl ethers to afford the silylated (2)-enol silyl ethers.Theme (3)"Asymmetric Transmission via Sequential Sigmatropic Rearrangements" : the sequential [2,3]-Wittig/oxy-Cope rearrangement of allyl cyclopentenyl ether was investigated. However, no work for evaluating the asymmetric transmission of the Sigmatropic sequence has been made yet.