BF3·OEt2 catalyzed chemoselective CC bond cleavage of α,β-enones: an unexpected synthesis of 3-alkylated oxindoles and spiro-indolooxiranes.

Abstract

A BF3·OEt2 catalyzed highly chemoselective formal CC double bond cleavage reaction of α,β-enones with diazoamides for the synthesis of 3-alkylated oxindoles is developed. Boron trifluoride etherate is found to be an effective catalyst for the chemoselective Cα-Cβ cleavage of enones to obtain 3-alkylated oxindoles. The product formation indicates a selective β-carbon elimination pathway of α,β-enones using the inexpensive BF3·OEt2 as a catalyst, transition metal-free conditions, an open-air environment, good functional tolerance and broad substrate scope. The synthetic utility of this protocol is highlighted by synthesizing spiro-indolooxiranes.