Synthesis of the alkaloids, 3′,4′-dimethoxy-2-(2-piperidyl)acetophenone, julandine, and cryptopleurine

Abstract

Condensation of (3,4-dimethoxybenzoyl)acetic acid (2) with enzyme-generated 3,4,5,6-tetrahydropyridine (3) gives 3′,4′-dimethoxy-2-(2-piperidyl)acetophenone (4) which, by reaction with p-methoxyphenylacetaldehyde followed by titanium(IV) chloride- or silicon(IV) chloride-catalysed cyclisation of the resulting enamine (6), leads to julandine (7); thallium(III) trifluoroacetate oxidation of (7) gives cryptopleurine (8) and, as a very minor product, the isomer (9).