The Ultrasound-Promoted Aluminum Amalgam Reduction of Phthalimides to Hydroxy Lactams

A new method for the reduction of N-substituted phthalimides to the corresponding hydroxy lactams is described which utilizes aluminum amalgam and is promoted by high-intensity ultrasound. The ultrasonic irradiation serves to rapidly fragment the amalgam creating a reactive dispersion as well as increasing mass transport between solution and surface thereby accelerating the reaction rate. While the yields of hydrbxy lactams derived from the corresponding phthalimides are in the range of 69–94%, both N-benzyl glutarimide and N-benzyl succinimide are not reduced. The reduction does not affect the double bond or ester function of a representative α,β-enoate ester.