Selective Ring Expansion and C−H Functionalization of Azulenes

Abstract

Abstract A transition metal-catalyzed ring expansion and C–H functionalization of azulene were developed. This work constitutes the first example of the ring expansion of azulene using Cu(hfacac)2 with diazo compound and chemoselectivity for C–H functionalization of azulene controlled by changing to AgOTf. A chemoselectivity can be controlled simply by changing the metal frame. This approach does not demand the addition of phosphine, NHC or related ligands and prefunctionalization of azulenes. In addition, the excellent functional group tolerance allows the synthesis of a wide range of 6,7-bicyclic compounds and C–H functionalized azulenes. A theoretical study was able to explain the experimental observations that copper catalysts afford the ring expansion product while silver catalysts result in the formation of C–H alkylation product.