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DOI: 10.1055/s-2003-38760
(-)-Sparteine in Asymmetric Synthesis
Publication History
Publication Date:
17 April 2003 (online)
Introduction
Asymmetric synthesis represents a challenging topic in modern organic chemistry. The asymmetric deprotonation of a prochiral carbon by a chiral base offers attractive access to a chiral carbanion, which may react to give enantioenriched products. (-)-Sparteine is a chiral bidentate ligand with broad applicability. Hoppe was the first to use a mixture of alkyllithium and (-)-sparteine (Figure 1) for very effective asymmetric deprotonations. [1] Beak examined enantioselective deprotonations of N-Boc-pyrrolidines and N-Boc-allylamines. [2] Furthermore, it was used for dynamic resolutions [3] and deprotonations [4] of phosphine-boranes, for asymmetric additions of alkyllithiums to imines, [5] for asymmetric carbometallations of cinnamyl derivatives, [6] for palladium-catalyzed oxidative kinetic resolutions of secondary alcohols, [7] and for enantioselective syntheses of ferrocenes with planar chirality. [8]
The title compound is an alkaloid, which can be isolated from certain papilionaceous plants such as Scotch broom. [9] Its antipode is also naturally occurring but can be obtained far less easily. An 18 steps asymmetric total synthesis of (+)-sparteine starting from norbornadiene has been reported. [10] A (+)-sparteine surrogate is readily available from (-)-cytisine. [11]
(-)-Sparteine is commercially available as a free base or as the sulfate-pentahydrate. The chiral ligand can usually be recovered from the reaction mixtures by alkaline extraction.
Figure 1
