Synthesis of Benzo[1,4]heterocycles using Palladium Catalyzed Heck Reaction to Vinylogous Carbonates/Carbamates: Unexpected Formation of Indoles via Carbopalladation Intercepted by Nucleopalladation

An efficient protocol for the stereoselective
synthesis of benzo­[1,4]­heterocycles
via palladium catalyzed Heck reaction on o-halo-aryl-oxa/thia/aza tethered vinylogous
carbonates/carbamates/esters has been developed. Unexpected formation
of indoles is observed when unprotected 2-iodoaniline tethered vinylogous
carbonates are subjected to the Heck reaction. Mechanistic studies
indicate that formation of these indoles is an outcome of the interception
of the carbopalladation step by nucleopalladation. The method can
be used to gain rapid access to the core skeleton of abacopterin A–C.