Spiroaminals - Crystal Structure and Computational Investigation of Conformational Preferences and Tautomerization Reactions

Derivatives of the triaminoguanidinium ion, 7: unsymmetrically substituted N,N ' ,N ''-triaminoguanidinium salts via a cyclopentanone spiroaminal intermediate

N,N′,N″-Triaminoguanidinium chloride (TAG-Cl) reacts with cyclopentanone or cyclohexanone to afford 8-(2-cyclopentylidenehydrazinyl)-6,7,9,10-tetraazaspiro[4.5]decan-8-ylium and 3-(2-cyclohexylidenehydrazinyl)-1,2,4,5-tetraazaspiro[5,5]undecan-3-ylium salts, respectively, i. e., two arms of the TAG ion were engaged in spiroaminal formation and the NH2 group of the third arm underwent imine-forming condensation. Ring-opening reactions of the cyclopentanone derived spiroaminal with aldehydes, aryl ketones, aromatic or aliphatic isocyanates give access to a variety of unsymmetrically substituted derivatives of the TAG ion.

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.

Synthesis and Reactions of Benzannulated Spiroaminals: Tetrahydrospirobiquinolines

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