Stereospecific Photoreduction of Polycyclic α,β-Unsaturated Ketones

Article abstract of DOI:10.1021/ja00275a050

The photolysis of 4a-methyl-4,4a,9,10-tetrahydro-2(3H)-phenenthrone (1) in isopropyl alcohol (i-PrOH) is found to give lumikeone rearrangement product 5 and reduction product 8 via the enone triplet ?,?^* excited state.Other reduction products 6,7, and 9, arise from the triplet n,?^* excited state.The lower limit of the energy of the triplet state E_n,?* is estimated to be ca. 67 kcal/mol above the ground state and that of the relaxed triplet ?,?^* excited state is ca. 61 kcal/mol.Reduction of the C=C bond on the enone chromophore from both excited states is stereospecific, with the twisted ?,?^* triplet leading exclusively to cis-fused bicyclic ketone and the planar n,?^* triplet to the trans fused isomer.The results from the photolysis of 4a-methyl-4,4a,5,6,7,8-hexahydro-2(3H)-naphthalenone (4) are consistent with these findings.