First asymmetric synthesis of a C2-symmetric 2-endo,6-endo-disubstituted bispidine

The enantioselective synthesis of a C₂-symmetric 2-endo,6-endo-disubstituted bispidine (3,7-diazabicyclo[3.3.1]nonane) has been accomplished for the first time. The key step was a Michael addition of the protected β-amino ester methyl (R)-3-{N-benzyl-N-[(S)-1-phenylethyl]amino}-3-phenylpropionate to its α-methylene derivative delivering an anti,anti-configured α,α′-methylene-bridged bis(β-amino ester) as the major diastereomer. Deprotection, reduction and cyclisation furnished (1R,2R,5R,6R)-2,6-diphenyl-3,7-bis((S)-1-phenylethyl)-3,7-diazabicyclo[3.3.1]nonane in six steps and 15% overall yield.