A synthesis of (±)-sparteine

Organic & Biomolecular Chemistry Pub Date: 2005-03-23 DOI: 10.1039/B502213D

Abstract

In a synthesis of racemic sparteine, Diels–Alder reaction between dimethyl bromomesaconate 14 and dicyclopentenyl 4, followed by cyclopropane formation, set up the stereochemistry at C-1 and C-5 as S and R, respectively, in a meso intermediate 8. The stereochemistry at C-2 and C-4 was then secured by a moderately diastereoselective protonation of the bis-enolate 17 derived from the diester 8 by reductive cleavage with lithium in liquid ammonia. The C[double bond, length as m-dash]C in the racemic diester 19 was ozonolysed and the diketone converted by Beckmann rearrangement into the bis-lactam 25. Reduction of the bis-lactam with lithium aluminium hydride and intramolecular nucleophilic displacement gave racemic sparteine 1. Some ideas for making this synthesis amenable to a synthesis of enantiomerically enriched sparteine are presented.

Graphical abstract: A synthesis of (±)-sparteine
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