Enantioselective Synthesis of Cyclobutanes via Sequential Rh- catalyzed Bicyclobutanation/Cu-catalyzed Homoconjugate Addition

摘要

Enantiomerically enriched cyclobutanes are constructed by a three-component process in which t-butyl (E)-2-diazo-5-arylpent-4-enoates are treated with Rh_2(S-NTTL)_4 to provide enantiomerically enriched bicyclobu-tanes, which can subsequently engage in homoconjugate addition/enolate trapping sequence to give densely functionalized cyclobutanes with high diastereoselectivity. This three-component, two-catalyst procedure can be carried out in a single flask. Rh_2(S-NTTL)_4-catalyzed reaction of t-butyl (Z)-2-diazo-5-phenylpent-4-enoate gives the Biichner cyclization product in excellent enantioselectivity.