Study on halolactamization-γ-hydroxylation or haloiminolactonization of 2,3-alkadienamides

The reactions of 4-mono- or 4-unsubstituted 2,3-alkadienamides with CuX2 afforded 5-hydroxypyrrol-2(5H)-ones via the sequential lactamization and γ-hydroxylation process in aqueous THF while those of 4,4-disubstituted 2,3-alkadienamides with CuX2 in THF afforded iminolactones in high yields. Iodoiminolactonization and iodolactamization/γ-hydroxylation were achieved by the corresponding reaction with I2 in THF at rt. The structures of the products depend on the steric hindrance at the 4-position of the starting allenamides. Relatively electron-rich allenes afforded the corresponding products in much higher yields under milder reaction conditions implying the intramolecular electrophilic nature of the cyclization reaction.