Solvent enaminoketones

Compound 220 in solution gives rise to a dynamic equilibrium between the enaminoketone (i )-220 and iV-acyl forms (Z)-221 in the ground state (Scheme 14). In nonpolar solvents, such as hexane, benzene, and toluene, the equilibrium is displaced toward isomer ( )-220, which is stabilized by intramolecular hydrogen bond it absorbs in the region of 470 nm. In polar solvents like DMSO, the equilibrium shifts almost completely toward the N-acylated form (Z)-221. 

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