Isobe Minoru, Chang Wei-Chung, Tsou Pei-Kang, Ploysuk Chatchawan, Yu Chin-Hui
Department of Chemistry, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan.
J Org Chem. 2015 Jun 19;80(12):6222-37. doi: 10.1021/acs.joc.5b00678. Epub 2015 Jun 3.
[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.
已对位于2-或4-位的糖衍生二氢吡喃烯丙基炔丙基醚的[2,3]-维蒂希重排进行了研究，它是通过手性转移来延长4-或2-位碳链的有用方法。这些反应的立体化学过程取决于以下因素：(1)前-R或前-S-H的去质子化；(2)锂化的立体异构碳负离子的平衡；(3)重排过程中的构象反转；(4)协同的[2,3]-或[1,2]-维蒂希重排。在某些情况下，涉及烯丙基-C-O键断裂的逐步机理是[2,3]-和[1,2]-维蒂希重排共同的第一步。比较锂化反应物之间重排的立体化学过程，以确定反应途径。多氧化二氢吡喃环系统中的这些机理得到了密度泛函理论计算的进一步支持。
