Bidirectional Synthesis of Di-tert-butyl (2S,6S,8S)- and (2R,6R,8R)‑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.