Diversity-Oriented Synthesis of Furo[3,2-c]coumarins and Benzofuranyl Chromenones through Chemoselective Acylation/Wittig Reaction.

A highly efficient and chemoselective one-pot protocol for the diversity-oriented synthesis of two types of coumarin-based formal cross-coupling adducts, furo[3,2-c]coumarins and 3-benzofuranyl chromenones, is described. Key attributes of the methodology are an initial chemoselective acylation of functionalized phosphorus zwitterions and a subsequent chemoselective intramolecular Wittig reaction that preferentially resulted in one of the two coumarin derivatives in high yield, depending on relative reactivities and the addition sequence of the acylating agents.