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 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 trifluoroacetyl 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.