TANDEM SONOGASHIRA-HAGIHARA COUPLING/CYCLO-ISOMERIZATION REACTIONS OF ETHYNYLBORONIC ACID MIDA ESTER TO AFFORD 2-HETEROCYCLIC BORONIC ACID MIDA ESTERS: A CONCISE ROUTE TO BENZOFURANS, INDOLES, FUROPYRIDINES AND PYRROLOPYRIDINES

摘要

A one-pot process that provides direct access to 2-heterocyclic MIDA (N-methyliminodiacetic acid) boronates has been developed. The reaction of 2-iodophenols or 2-iodoanilines with ethynylboronic acid MIDA ester readily afforded 2-substituted heterocyclic compounds. Amidine and phosphazene bases, especially TMG (1,1,3,3-tetramethylguanidine) assumed an important role in the tandem Sonogashira-Hagihara coupling/cycloisomerization reactions.