Steric effects in the reactions of αβ-unsaturated ketonep-tolylsulphonylhydrazones: a route to 1,2-benzodiazepines via 1,7-ring closure of 1,1-diaryl-3-diazoalkenes

Abstract

The influence of steric effects and substituents on the reactions of the sodium salts of αβ-unsaturated ketone tosylhydrazones has been studied. The tosylhydrazone salts of acyclic αβ-unsaturated ketones and those of 2-methylenecyclohexanones underwent ready thermal 1,5-ring closure to give pyrazoles but the reactions of some 2-methylenecyclopentanone tosylhydrazones were atypical. Although 2-methylenecyclopentanone tosylhydrazone salts having a β-hydrogen atom cyclised to give 1H-pyrazoles in high yield, the ββ-dialkyl and the ββ-diaryl analogues both failed to give 3H-pyrazoles; the former decomposed by a carbenic route to give dienes and the latter underwent 1,7-ring closure to give 3H-1,2-benzodiazepines. The effect of solvent proticity on some of these reactions has been investigated, and the mechanisms of pyrazole and benzodiazepine formation are discussed. The ¹³C n.m.r. spectra of 3H-pyrazoles, 3H-1,2-benzodiazepines, and 1H-2,3-benzodiazepines show that ring size strongly affects the chemical shift of the saturated carbon atom attached to the azo-group.