I. [2 +2] Cycloaddition and benzannulation of 2-iodoynamides and application to the construction of highly substituted indoles : II. Synthesis of furo[2,3-g]thieno[2,3-e]indole via a benzannulation strategy

Abstract

The synthesis and reactions of 2-iodoynamides were investigated. 2-Iodoynamides undergo efficient and regioselective [2 + 2] cycloaddition with ketene to produce cyclobutenones that are useful synthetic building blocks. Reaction of 2-iodoynamides and vinylketenes generated in situ from cyclobutenones proceeds via a pericyclic cascade mechanism to produce highly substituted 2-iodoanilines. Tandem strategies for the synthesis of highly substituted indoles involving this benzannulation reaction were investigated. In addition, the synthesis of furo[2,3-g]thieno[2,3- e]indole, a new tetracyclic aromatic compound, was achieved via a strategy based on benzannulation with ynamides.