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

Abstract

Enantiomerically enriched cyclobutanes are constructed by a three-component process in which <i>t</i>-butyl (<i>E</i>)-2-diazo-5-arylpent-4-enoates are treated with Rh₂(<i>S</i>-NTTL)₄ to provide enantiomerically enriched bicyclobutanes, 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. Rh₂(<i>S</i>-NTTL)₄-catalyzed reaction of <i>t</i>-butyl (<i>Z</i>)-2-diazo-5-phenylpent-4-enoate gives the Büchner cyclization product in excellent enantioselectivity