Construction of an Angular Tricyclic Benzofuran Skeleton Using the C–H Activation Strategy

A protocol for the construction of an angular tricyclic benzofuran skeleton based on the C–H activation strategy has been established. Different phthalide lactones on this skeleton can be easily assembled with various side chains by using C–H activation with aldehydes and subsequent reduction. This skeleton provides a versatile and crucial motif for the total synthesis of naturally occurring angular tricyclic benzofurans and their derivatives. Based on this protocol, the improved total syntheses of daldinin A and annullatin D were achieved in yields of 17.3 and 7.6%, respectively.