Palladium-Catalyzed Asymmetric Cycloadditions of Vinylcyclopropanes and in Situ Formed Unsaturated Imines: Construction of Structurally and Optically Enriched Spiroindolenines

A palladium-catalyzed
(3 + 2) cycloaddition of vinyl cyclopropane
and α,β-unsaturated imines generated in situ from aryl
sulfonyl indoles is reported. The reaction proceeds with high diastereoselectivity
to provide the optically enriched spirocyclopentane-1,3′-indolenines
in up to 74% yield and with up to 97% ee, which contains an all-carbon
quaternary center and two tertiary stereocenters. The reaction involves
a first conjugate addition of the carbon anion of zwitterionic π-allylpalladium
complex from vinyl cyclopropane to the in situ formed unsaturated
imine followed by a palladium-catalyzed intramolecular C3-allylation of indole.

本研究报道了钯催化的、由芳基磺酰基吲哚原位生成的α,β-不饱和亚胺与乙烯基环丙烷的(3+2)环加成反应。该反应具有优异的非对映选择性，可得到光学富集的螺环戊烷-1,3′-吲哚宁类产物，产率最高可达74%，对映体过量值（enantiomeric excess, ee）最高达97%；该产物含有一个全碳季碳中心与两个叔立体中心。反应机理为先由乙烯基环丙烷衍生的两性离子π-烯丙基钯配合物的碳负离子对原位生成的不饱和亚胺发生共轭加成，随后进行钯催化的吲哚分子内C3位烯丙基化反应。