Quinoline alkaloids. Part XVI. 2,2-Dimethylpyranoquinolines from base-catalysed rearrangement of isoprenyl epoxides. Synthesis and biogenesis of flindersine

Abstract

The reaction of 3-isoprenyl-2,4-dimethoxyquinoline epoxides with potassium hydroxide in aqueous dimethyl sulphoxide furnished 2,2-dimethylpyranoquinolines in high yield, and led to a new synthesis of the alkaloid flindersine. A mechanistic study resulted in the isolation of an allylic alcohol intermediate and the detection of a second allylic alcohol, and indicated that quinone methides were involved in the cyclisation step. The biogenesis of flindersine and related compounds is discussed.