Synthesis of Benzomacrolactam by 11–endo Selective Aryl Radical Cyclization of 2–Iodobenzamide Derived from D–Galactose

Encouraged by our previous studies of tri-n-butyltin-mediated radical cyclization reaction of o-iodobenzamides, we applied this methodology to the synthesis of benzomacrolactam 2 from methyl 4-O-allyl-2,3-di-O-benzyl-6-deoxy-6-(2-iodobenzoylamino)- α-D-galactopyranoside 1. Apart from the macrolactam 2, resulting from regioselective 11-endo aryl radical cyclization, the hydrogenolysis produt 3 was obtained. The o-iodobenzamide 1 was prepared in eight conventional synthetic steps from methyl α-D-galactopyranoside. The unequivocal structures of 1, 2 and 3 were supported by ¹H, 13C and DEPT NMR spectroscopy and by COSY and HMQC experiments.