Bidirectional Synthesis of Di-<i>tert</i>-butyl (2<i>S</i>,6<i>S</i>,8<i>S</i>)- and (2<i>R</i>,6<i>R</i>,8<i>R</i>)‑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 <i>tert</i>-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

Synthesis and Reactions of Benzannulated Spiroaminals: Tetrahydrospirobiquinolines

An efficient two-step synthesis of symmetrical and unsymmetrical tetrahydrospirobiquinolines from <i>o</i>-azidobenzaldehydes is reported. A novel series of tetrahydrospirobiquinolines was prepared by sequential double-aldol condensation with acetone, cyclopentanone, and cyclohexanone to form the corresponding <i>o</i>,<i>o</i>′-diazido-dibenzylidene-acetone, -cyclopentanone, and -cyclohexanone derivatives, respectively, and hydrogenation–spirocyclization. The spirodiamines were further derivatized by electrophilic aromatic bromination, Suzuki coupling, and <i>N</i>-alkylation, all of which proceeded with preservation of the spirocyclic core

Bidirectional Synthesis of Di-<i>tert</i>-butyl (2<i>S</i>,6<i>S</i>,8<i>S</i>)- and (2<i>R</i>,6<i>R</i>,8<i>R</i>)‑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 <i>tert</i>-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