Overcrowded molecules. Part VI. Photocyclisation of cis-9a,10-dihydro-9-methyl-10,15-diphenyl-9H-benzo[5,6]indeno[2,1-c] phenanthrene

Abstract

Diphenylketen reacts with (E)-2-benzylidene-2,3-dihydro-3-methyl-2,3-dihydrocyclopenta[c]phenanthrene-1-one at 180° to yield cis-9a, 10-dihydro-9-methyl-10,15-diphenyl-9H-benz[5,6]indeno[2,1-c]phenanthrene having an anti-arrangement of methyl and 10-phenyl groups. This overcrowded hydrocarbon undergoes photocyclisation by the less hindered of the two allowed controtatory processes to give 5a, 6,10b,13e-tetrahydro-5-methyl-6,10b-diphenyl 5H-cyclopenta[def]naphtho[8,1,2-pqr]chrysene having a cis-arrangement of 5a-, 6, and 13e-hydrogens and the methyl group anti to both phenyl groups.