Photoreaction of homobenzoquinones with amine donors

The photoreactions of diphenylhomobenzoquinones 1a-d bearing 2-bromo and 2-methyl substituents have been investigated in the presence of amine donors, The products of these reactions are much dependent on the substituents and the nature of added amines, Irradiation of l-bromo substituted diphenylhomobenzoquinone la with triethylamine (TEA) resulted in ring-opening of the fused-cyclopropane moiety to give 2-diphenylmethyl-1,4-benzoquinone 3a. However, the photoreaction of la with N,N-dimethylaniline (DMA) yielded the 1:1 aminated bicyclic dione 4a and bis(p-dimethylaminophenyl)methane 7 along with 3a, In contrast, irradiation of 1-methyl substituted diphenylhomobenzoquinones 1b-d with TEA brought about hydrogenation of the C=C double bond to give the bicyclic diones 8b-d. Similar photoreaction of Ib,c with DMA provided only the 1:1 aminated bicyclic diones 4b,c, although the trimethyl substituted id remained essentially intact.