Centre for Sustainable Chemical Processes, Department of Chemistry, Durham University University, Science Laboratories , South Road, Durham DH1 3LE, U.K.
J Org Chem. 2017 Jul 21;82(14):7265-7279. doi: 10.1021/acs.joc.7b00854. Epub 2017 Jun 30.
Homoallylic boronate carboxylate esters derived from unsaturated aldehydes via an imination, β-borylation, imine hydrolysis, and Wittig trapping sequence, were subjected to a second boryl addition to give 1,3-diborylated carboxylate esters. Control of the absolute and relative stereochemistry of the two new 1,3-stereogenic centers was achieved through: (1) direct chiral catalyst controlled asymmetric borylation of the first stereocenter on the unsaturated imine with high e.e.; and (2) a double diastereoselectively controlled borylation of an unsaturated ester employing a chiral catalyst to largely overcome directing effects from the first chiral boryl center to give poor (mismatched) to good (matched) diastereocontrol. Subsequently, the two C-B functions were transformed into C-O systems to allow unambiguous stereochemical assignment of the two borylation reactions involving oxidation and acetal formation.
通过亚胺化、β-硼化、亚胺水解和维蒂希捕捉序列，从不饱和醛衍生出的偕烯丙基硼酸盐羧酸酯，经第二次硼加成得到 1,3-二硼化羧酸酯。通过以下两种方法控制两个新的 1,3-手性中心的绝对和相对立体化学：(1) 通过直接手性催化剂控制不对称硼化，高对映选择性地对不饱和亚胺的第一个立体中心进行硼化；(2) 对不饱和酯进行双非对映选择性控制硼化，使用手性催化剂，以克服第一个手性硼基中心的定向效应，从而得到较差（不匹配）到较好（匹配）的非对映选择性控制。随后，将两个 C-B 官能团转化为 C-O 系统，以允许对涉及氧化和缩醛形成的两个硼化反应的立体化学进行明确的立体化学归属。
