10.1016/j.tetasy.2007.06.010
The study details the enantioselective synthesis of a C2-symmetric 2-endo,6-endo-disubstituted bispidine (3,7-diazabicyclo[3.3.1]nonane). The key chemical involved is the protected b-amino ester methyl (R)-3-{N-benzyl-N[(S)-1-phenylethyl]amino}-3-phenylpropionate, which undergoes a Michael addition to its a-methylene derivative to form an anti,anti-configured a,a-methylene-bridged bis(b-amino ester) as the major diastereomer. This intermediate is then transformed into the final product, (1R,2R,5R,6R)-2,6-diphenyl-3,7-bis((S)-1-phenylethyl)-3,7-diazabicyclo[3.3.1]nonane, through deprotection, reduction, and cyclization steps. The synthesis is significant as it provides a new route to C2-symmetric bispidines, which have potential applications in asymmetric synthesis as chiral ligands or backbones for Lewis acids. The study also explores various synthetic routes and conditions to optimize the yield and diastereoselectivity of the key Michael addition step, ultimately achieving the target compound in six steps with a 15% overall yield.