Relative tendency of carbonyl compounds to form enamines.
Equilibria between carbonyl compounds and their enamines (from O-TBDPS-derived prolinol) have been examined by NMR spectroscopy in DMSO-d(6). By comparing the exchange reactions between pairs (enamine A + carbonyl B → carbonyl A + enamine B), a quite general scale of the tendency of carbonyl groups to form enamines has been established. Aldehydes quickly give enamines that are relatively more stable than those of ketones, but there are exceptions to this expected rule; for example, 1,3-dihydroxyacetone acetals or 3,5-dioxacyclohexanones (2-phenyl-1,3-dioxan-5-one and 2,2-dimethyl-1,3-dioxan-5-one) show a greater tendency to afford enamines than many α-substituted aldehydes.
Departament de Química Orgànica, Facultat de Química, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Catalonia, Spain.
Dani
D
Sánchez
David
D
Bastida
Jordi
J
Burés
Carles
C
Isart
Oriol
O
Pineda
Jaume
J
Vilarrasa