Synthesis of benzocycloheptenones by 1,3-dipolar additions of 2-(1,3-benzodioxol-5-ylmethyl)-4-hydroxy-3-methoxy-carbonylisoquinolin-2-ium chloride with dipolarophiles

Abstract

The addition of thionyl chloride to dihydroisoquinolines affords isoquinolinium chlorides which are readily converted to the corresponding ylides upon treatment with sodium hydrogen carbonate. These ylides undergo facile 1,3-dipolar additions with dimethyl acetylenedicarboxylate, maleic anhydride and acrylonitrile to afford the corresponding benzocycloheptenone cycloadduct.