Halogen Dance on 2‐Iodobenzofuran and 2‐Iodobenzothiophene and Related Reactions

Abstract

AbstractWhen 2‐iodobenzofuran was treated sequentially with lithium 2,2,6,6‐tetramethylpiperidide in tetrahydrofuran at −50 °C and an aldehyde, the 2‐substituted 3‐iodobenzofuran resulting from the halogen dance was the only isolated product. However, from 2‐iodobenzothiophene, these conditions led to mixtures in which the 2‐substituted 3‐iodobenzothiophene was always accompanied by the 2‐substituted benzothiophene. The use of 2‐bromobenzothiophene as a catalyst made it possible to significantly reduce this competitive dehalogenation. To confirm the halogen dance reaction, the products were unambiguously synthesized by using direct halogenations and deprotolithiation‐trapping sequences as key steps. Our efforts to access 2,7‐disubstituted and 7‐substituted derivatives of benzofuran and benzothiophene have also been reported.