5-Substituted Derivatives of the Tricyclic (+)-Sparteine Surrogate in the Enantioselective Lithiation/Stannylation of an O-Alkyl Carbamate

摘要

5-Mono- and 5,5-disubstituted tricyclic bispidines, derivatives of the known (+)-sparteine surrogate, have been synthesized in four-to-six steps from the natural alkaloid (–)-cytisine and evaluated as chiral ligands in the enantioselective lithiation/stannylation of an O-alkyl carbamate. Structure-selectivity studies revealed that a small 5-endo substituent is tolerated, whereas larger 5-endo substituents and even small 5-exo substituents lead to significantly reduced levels of chirality transfer.