Nucleophilic Cyclization of o‐Alkynylbenzamides Promoted by Iron(III) Chloride and Diorganyl Dichalcogenides: Synthesis of 4‐Organochalcogenyl‐1H‐isochromen‐1‐imines

Abstract

AbstractWe have developed a method for the preparation 4‐organochalcogenyl‐1H‐isochromen‐1‐imines from o‐alkynylbenzamides. This electrophile‐promoted nucleophilic cyclization achieved by treatment with a combination of iron salts and diorganyl dichalcogenides. FeCl3 and diorganyl dichalcogenides reacted with o‐alkynylbenzamides under aerobic conditions at room temperature and in the absence of additives to give 4‐organochalcogenyl‐1H‐isochromen‐1‐imines in good yields and with good selectivities. The reaction took place with 0.5 equiv. of the diorganyl dichalcogenides, which demonstrates that both halves of the diorganyl dichalcogenides (RYYR → 2RY) were incorporated into the final product. Mechanistic studies suggested that the regioselectivity of the cyclization is governed by a seleniranium ion, a key intermediate formed by the electrophilic addition of the organochalcogen moiety to the carbon–carbon triple bond. The utility of the 4‐organochalcogenyl‐1H‐isochromen‐1‐imines was also demonstrated by their application as starting materials in Suzuki and Sonogashira cross‐coupling reactions.