Direct Catalytic Desaturation of Lactams Enabled by Soft Enolization.

Abstract

A direct catalytic method is described for the α,β-desaturation of N-protected lactams to their conjugated unsaturated counterparts under mildly acidic conditions. The reaction is consistently operated at room temperature and tolerates a wide range of functional groups, showing reactivity complementary to that of prior desaturation methods. Lactams with various ring sizes and substituents at different positions all reacted smoothly. The synthetic utility of this method is demonstrated in a concise synthesis of Rolipram. In addition, linear amides also prove to be competent substrates, and the phthaloyl-protected product serves as a convenient precursor to access various conjugated carboxylic acid derivatives. Strong bases are avoided in this desaturation approach, and the key is to merge soft enolization with a Pd-catalyzed oxidation process.