Overcrowded molecules. Part XII. Thermal and photochemical reactions of (2Z,3Z)-and (2Z,3E)-2-benzylidene-2,3-dihydro-3-mesityl(phenyl)-methylenebenzofuran

Abstract

(2Z,3Z)-2-Benzylidene-2,3-dihydro-3-mesityl(phenyl)methylenebenzofuran thermally isomerises to the (2Z,3E)-diene, which undergoes thermal disrotatory ring closure followed by a [1,5] hydrogen shift to yield cis-5a,6-dihydro-11-mesityl-6-phenylbenzo[b]naphtho[2,3-d]furan. Irradiation of the (2Z,3Z)-diene causes conversion into the (2Z,3E)-diene and photocyclisation by the conrotatory mode to the trans-6,7a-dihydro-intermediate, which undergoes a [1,5] hydrogen shift to give the trans-5a,6-dihydrobenzonaphthofuran derivative at 80 °C or above, and is oxidised by oxygen.