Phototransformations of bridgehead-disubstituted dibenzobarrelenes. Interesting rearrangements of dibenzosemibullvalene intermediates derived from 9-(hydroxyalkyl)-10-methoxy-substituted dibenzobarrelenes
- Regional Research Lab. (CSIR), Trivandrum (India); and others
The photochemistry of 11,12-dibenzoyl-9,10-dihydro-9-(hydroxymethyl)-10-methoxy-9,10-ethenoanthracene and 11,12-dibenzoyl-9,19-dihydro-9-(1-hydroxyethyl)-10-methoxy-9,10-ethenoanthracene has been studied through steady-state photolysis, product analysis, and laser flash photolysis. Irradiation of 7a in benzene, methanol, or acetone gave 69-72% yields of a dibenzopentalene ketone 11a, arising through a dibenzosemibullvalene precursor. Irradiation of 7b, which exists in equilibrium with its cyclic form 7b{prime}, gave a mixture of the dibenzopentalene ketone 11b (41%) and the dibenzopentalenopyran derivative, 16b{prime} (26%). The photochemistry of 11,12-dibenzoyl-9,10-dihydro-9,10-dimethoxy-9,10-ethenoanthracene (17) has been reinvestigated. Irradiation of 17 in benzene and methanol gives a 90% yield of an isomeric pentacyclic product 24, formed through the rearrangement of a dibenzosemibullvalene precursor. Irradiation of 17 in aqueous methanol gives a mixture of the dibenzopentalene ketone 22 (40%) and a pentacyclic methanol adduct 21 (34%). The structures of 7b{prime}, 11a,b,16b{prime},21, and 24 were confirmed through X-ray crystallographic analysis. The 308 nm laser flash photolysis of 1a,b in benzene results in the formation of their triplets ({phi}{sup T} = 0.55-0.76). These triplets possess short lifetimes (0.45-0.75 {mu}s) and are quenched by oxygen, 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO), 4-hydroxy-2,2,6,6- tetramethylpiperidinyl-1-oxy (HTEMPO), ferrocene, and {beta}-carotene at rates in the range (0.26-4.7) x 10{sup 9} M{sup -1} s{sup -1}. 21 refs., 1 fig., 1 tab.
- OSTI ID:
- 494164
- Journal Information:
- Journal of Organic Chemistry, Vol. 61, Issue 16; Other Information: PBD: 9 Aug 1996
- Country of Publication:
- United States
- Language:
- English
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