Synthesis of thieno[2,3-b]indoles by Cloke–Wilson rearrangement of spiro donor–acceptor cyclopropanes

Abstract

A one-pot synthesis of thieno[2,3-b]indoles is reported via a Lawesson's reagent-mediated thiocarbonyl Cloke–Wilson rearrangement of spiro donor–acceptor cyclopropyl oxindoles, followed by oxidative aromatization under open–air conditions. The reaction proceeds smoothly under mild conditions, tolerates a range of aryl substrates, and can be performed on a synthetically relevant scale. Control experiments and DFT studies indicate a stepwise rearrangement pathway in which aerial oxygen promotes a barrier-less aromatization driven by aromatic stabilization. This work demonstrates the versatility of donor–acceptor cyclopropanes as efficient building blocks for the construction of sulfur-containing fused heteroaromatic frameworks.