Isolation, structure and reaction of selenobenzophenones. X-Ray molecular structure of 4,4′-dimethoxyselenobenzophenone and of 4,4-biphenyl-2,3-diselenabicyclo[3.3.0]oct-7-ene

Abstract

4,4′-Dimethoxy-1a and 4,4′-dimethyl-selenobenzophenone 1b could be isolated in moderate yields by the reaction of the corresponding ylides 3 with elemental selenium in benzene at 80 °C. Their spectral data are described. Attempted isolation of unsubstituted selenobenzophenone afforded only its dimer 5. Compound 1a crystallizes in space group P2₁/n with unit-cell parameters a= 7.191(3), b= 7.505(4), c= 24.856(4)Å, β= 90.32(1)°, Z= 4, R= 0.055. The oxidation and thiation of 4,4′-dimethoxyselenobenzophenone 1a afforded the corresponding benzophenone and thiobenzophenone in good yields. The reaction of compound 1 with cyclopentadiene afforded the corresponding cycloadducts 7(3,3-diaryl-2-selenabicyclo[2.2.1] hept-5-enes), whereas bicyclic diselenides 8(4,4-diaryl-2, 3-diselenabicyclo[3.3.0]oct-7-enes) were obtained by using an excess of selenium and a higher temperature. Oxidation of compound 8c gave the corresponding diol 12, aldehyde 13, and diphenylfulvene 11. The reaction of compound 1a with benzenediazonium carboxylate afforded 2,2- bis-(4-methoxyphenyl)-4H-3,1 -benzooxaselenin -4-one 17.