Abstract：
A stereoselective hydroxyallylation reaction of cyclopropenes with cyclopropanols is achieved under zinc-mediated conditions, affording densely functionalized cyclopropanes with excellent diastereocontrol over three contiguous stereocenters within and outside the cyclopropane ring. A racemic variant of the reaction is synergistically promoted by catalytic N-heterocyclic carbene (NHC) and organic base, whereas chiral amino alcohol-derived bifunctional NHC enables a catalytic enantioselective variant. The reaction likely involves the generation of enolized zinc homoenolate via ring-opening of zinc cyclopropoxide and enolization of the resulting homoenolate, followed by its addition to the cyclopropene as a prochiral allylzinc nucleophile. Our mechanistic investigations highlighted the transient nature of enolized homoenolate, which, once generated from thermodynamically predominant cyclopropoxide, immediately proceeds to allylzincation with cyclopropene. The NHC not only promotes the rate-determining generation of enolized homoenolate but also engages in the allylzincation process. The resulting cyclopropylzinc species undergoes partial in situ protonation while partially remaining intact, thereby leaving an opportunity for trapping with an external electrophile.
摘要：
在锌介导的条件下，可以实现环丙烯与环丙醇的立体选择性羟基烯丙基化反应，在环丙烷环内和外的三个连续的立体中心上提供具有优异的非对映控制的致密官能化环丙烷。催化的N-杂环卡宾（NHC）和有机碱协同促进了反应的外消旋变体，而手性氨基醇衍生的双功能NHC能够实现催化对映选择性变体。该反应可能涉及通过环丙氧基锌的开环和生成的均烯醇化物的烯醇化来生成烯醇化均烯醇锌，然后将其添加到环丙烯中作为前手性烯丙基锌亲核试剂。我们的机理研究强调了烯醇化高烯醇化物的短暂性，which,一旦从热力学占优势的环丙氧基产生，立即用环丙烯进行烯丙基锌化。NHC不仅促进烯醇化均烯醇化物的速率决定生成，而且还参与烯丙基锌化过程。所得的环丙基锌物种经历部分原位质子化，同时部分保持完整，从而留下用外部亲电子试剂捕获的机会。
