title: Stereochemical Course of Wittig Rearrangements of Dihydropyran Allyl Propargyl Ethers.
abstract: [2,3]-Wittig rearrangements of sugar-derived dihydropyran allyl propargyl ethers located at the 2- or 4-position have been studied as useful means for extending the carbon chains of the 4- or 2-position with chirality transfer. The stereochemical course of these reactions depends on the following factors: (1) deprotonation of pro-R or pro-S-H, (2) equilibration of the lithiated stereogenic carbanion, (3) conformational inversion during the rearrangement, and (4) concerted [2,3]- or [1,2]-Wittig rearrangement. In some cases, a stepwise mechanism that involves the allyl-C-O bond cleavage is shared as the first step by both the [2,3]- and [1,2]-Wittig rearrangements. The stereochemical courses of the rearrangements are compared among the lithiated reactants to determine the reaction pathways. These mechanisms in the polyoxygenated dihydropyran ring system were further supported by DFT calculations.
authors.affiliation: Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Isobe
authors.affiliation: Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan.
authors.forename: Wei-Chung
authors.initials: WC
authors.lastname: Chang
authors.affiliation: Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan.
authors.forename: Pei-Kang
authors.initials: PK
authors.lastname: Tsou
authors.affiliation: Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan.
authors.forename: Chatchawan
authors.initials: C
authors.lastname: Ploysuk
authors.affiliation: Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan.
authors.forename: Chin-Hui
authors.initials: CH
authors.lastname: Yu