The preparation and photolysis of (E)-1-Aryl-3-methyl-3-phenylbut-1-enes

Abstract

Reaction of 2-methyl-2-phenylpropylmagnesium chloride with benzaldehyde in tetrahydrofuran gave 2,7-dimethyl-2,4,5,7-tetraphenyloctane-4,5-diol as a 1 : 2 mixture of clear transparent crystalline plates (meso) and needles (±), 3-methyl-1,3-diphenylbutan-1-one, benzyl alcohol, 2-methyl-2-phenylpropaneand a low yield of 3-methyl-1,3-diphenylbutan-1-ol. The distinction between the meso and the (+)- diols was unequivocal because the unique space group of the former requires thedimeric molecules to lie about a crystallographic centre of symmetry. The mechanism involved in the formation of the products of the Grignard reaction is examined. By careful choice of reaction conditions a series of I-aryl-3-methyl-3-phenylbutan-1-ols were prepared. Dehydration of the 1-aryl-3-methyl-3-phenylbutan-1-ols with p-toluene sulfonic acid and a short reaction time gives(E)-1-aryl-3-methyl-3-phenylbut-1-enes but longer reaction times afford 3-aryl-1,1-dimethylindanes.Photolysis of the (E)-1-aryl-3-methyl-3-phenylbut-1-enes affords (Z)-1-aryl-3-methyl-3-phenylbut-1-enes and trans-1-aryl-3,3-dimethyl-2-phenylcyclopropanes. Extended photolysis gives 4-aryl-2-methyl-3-phenylbut-1-enes via trans-1-aryl-3,3-dimethyl-2-phenylcyclopropane by rupture of the cyclopropyl bond adjacent to the aryl substituent.