Synthesis and Reactions of Benzannulated Spiroaminals: Tetrahydrospirobiquinolines

Bidirectional Synthesis of Di- tert-butyl (2 S,6 S,8 S)- and (2 R,6 R,8 R)-1,7-Diazaspiro[5.5]undecane-2,8-dicarboxylate and Related Spirodiamines

Efficient syntheses of both enantiomers of a spirodiamine diester from (l)- and (d)-aspartic acid are described. The key transformation was the conversion of Boc-protected tert-butyl aspartate into the derived aldehyde, two-directional Horner-Wadsworth-Emmons olefination, hydrogenation, and selective acid-catalyzed Boc-deprotection and spirocyclization. An alternative, two-directional approach to derivatives of 1,7-diazaspiro[5.5]undecane is described.