Chemical Transformation of Protoberberines. XV. : A Novel and Efficient Method for the Introduction of Alkyl Groups on the C-13 Position in the Protoberberine Skeleton

Abstract

The Wittig reaction of 8, 14-cycloberbin-13-ones (4), derived from the corresponding protoberberine alkaloids (2), with methylenetriphenylphosphorane afforded 13-methylene-8, 14-cycloberbines (5). Irradiation of 5 with a 100 W high pressure mercury lamp effected photochemically-induced electrocyclic fission of the aziridine ring to yield 13-methylberberine (1a), dehydrocorydaline (1b), and corysamine (1c) in high yield. Introduction of ethyl and propyl groups on the C-13 position in 2 was also conveniently achieved via photochemical reaction of the corresponding alkylidene derivatives (8 and 9, respectively).