Syntheses of (±)-tetrahydropalmatine and spirobenzylisoquinolines by thermolysis of benzocyclobutene derivatives

Abstract

The tetrahydroprotoberberine alkaloid, (±)-tetrahydropalmatine (1) was synthesized by heating the 1-benzocyclobutenyl-3,4-dihydroisoquinoline (16), followed by reduction of the dehydro compound (20) with sodium borohydride. Ochotensine type spirobenzylisoquinolines (18) and (19) were prepared by the electrocyclic reaction of the corresponding benzocyclobutene derivatives (14) and (15).