Synthesis of Lactams and Diazepanones via Beckmann Rearrangement

Significance

The facile Beckmann rearrangement of oxime mesitylenesulfonates, prepared in situ from the corresponding cyclic and acyclic ketoximes, is described. Treatment of ketoximes 1, 3 and 5 with mesitylsulfonyl chloride in THF and with lithium hydroxide as base, led to the rapid formation of lactams 2 and 4 and amides 6, in many cases in excellent yield. The use of benzene- or toluenesulfonyl chloride led to decreased yields which is attributed to the increased leaving group ability of the bulky mesitylenesulfonate moiety. Lithium hydroxide was found to be the optimal base due to its increased solubility in the reaction solvent.