Construction of oxabicyclo[3.2.1]octanes via palladium-catalyzed intermolecular [3 + 4] cycloadditions of vinylidenecyclopropane-diesters with pyrroles or indoles bearing a trifluoroacetyl group and the related hydroamination reaction

Abstract

In this paper, we reported a palladium-catalyzed rapid construction of oxabicyclo[3.2.1]octane skeletons through an intermolecular [3 + 4] cycloaddition of vinylidenecyclopropane-diesters (VDCP-diesters) with pyrroles and indoles bearing a trifluoroacetyl group at the 2-position under mild conditions. This cycloaddition proceeds through a key zwitterionic π-propargyl palladium species derived from a VDCP-diester, affording the corresponding cycloadducts in moderate to good yields and ee values, along with good substrate applicability. The strong electron-withdrawing effect of the trifluoroacetyl group is essential for this [3 + 4] cycloaddition reaction. Replacing it with other acyl groups triggers the reconstruction of the cyclopropane ring to produce a series of vinylcyclopropane products (VCP products) through a hydroamination reaction pathway. The plausible reaction mechanisms are proposed on the basis of control and deuterium-labeling experiments as well as a Fukui function analysis.