Electrocyclic reactions. Part 11. 1,5-Diphenylpentadienide

Abstract

1,5-Diphenylpentadienide, generated from trans,trans-dibenzylideneacetone p-tolylsulphonylhydrazone by the Caglioti reaction with lithium aluminium hydride, furnished cis-3,4-diphenylcyclopentenide, which by a suprafacial [1,4] sigmatropic shift and proton acquisition afforded 1,5-diphenylcyclopentene (18%); the other main products were toluene-p-sulphonamide and 1,5-diphenylpentan-3-imine (68%), formed by fission of the N–N bond of the sulphonyl hydrazone and reduction. Treatment of the sulphonylhydrazone with sodium methoxide in methanol thermally or photochemically yielded only 3(5)-phenyl-5(3)-styrylpyrazole. 3-Methoxy-1,5-diphenylpenta-1,4-diene with sodium–potassium alloy gave only cis- or trans-1,5-diphenylpent-2-ene.