Curtius rearrangement reactions of 3-(4-azidocarbonyl) phenylsydnone. Synthesis of 4-(sydnon-3-yl) phenyl carbamates, N-aryl-N¢-[4-(sydnon-3-yl)] phenyl ureas and their antimicrobial and insecticidal activities

3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a–h), 4,4-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a–l). Compounds (5a–l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a–l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a–l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been found to be more toxic against fourth instar larvae of Aedes aegypti, in particular, the n-butyl derivative (3e).