Photochemistry of organic multichromophoric molecules and reaction selectivity-I : reactions of (+) -4α -acetyl-2-carene

Monoterpenoids

“…358 Photolysis of the methoxy-ketone (354), in ethanol solution, gives the cleavage product (359, while its epimer (356) yields (357) and (358), which are the known irradiation products of cis-caran-4-one (359). 359 The hydrogenation of the unsaturated alcohol (360) over palladized charcoal at 80°C to yield (361)- (363) has been described.360 Treatment of the allylic chloride (364) gives a low yield of the caradiene (365). 361 The tosylate (366) can be converted into the inverted nitrile (367), which is hydrolysed (with epimerization) to the a-acid (368).…”

“…If the irradiation is through a Corex filter, and (349) is in solution in acetone, the products are the cyclopentenes (352) and (353). 358 Photolysis of the methoxy-ketone (354), in ethanol solution, gives the cleavage product (359, while its epimer (356) yields (357) and (358), which are the known irradiation products of cis-caran-4-one (359). 359 The hydrogenation of the unsaturated alcohol (360) over palladized charcoal at 80°C to yield (361)- (363) has been described.360 Treatment of the allylic chloride (364) gives a low yield of the caradiene (365).…”

Skeletal rearrangements of monoterpenoids of the carane series

“…Irradiation of 4-acetyl-2-carene (42) in the presence of a sensitiser gives products with the bicyclo[3.2.0]heptane structure, 43 i.e., replacement of a hydroxymethyl group by an acyl group does not alter the mechanism.…”

“…However, irradiation of the ketone 42 in the absence of sensitisers results in a fundamentally different rearrangement leading to the product of a 1,3-acyl shift [2-acetyl-3-carene (43)] and to tricyclic alcohols, i.e., the Norrish type II cyclisation products of both ketones present in the reaction medium. 43 A somewhat unusual behaviour of cis-(44) and trans-4caranone ( 45) is observed in their irradiation.…”

“…However, irradiation of the ketone 42 in the absence of sensitisers results in a fundamentally different rearrangement leading to the product of a 1,3-acyl shift [2-acetyl-3-carene (43)] and to tricyclic alcohols, i.e., the Norrish type II cyclisation products of both ketones present in the reaction medium. 43 A somewhat unusual behaviour of cis-(44) and trans-4caranone ( 45) is observed in their irradiation. Although the structures of these molecules enable the Norrish type II cleavage of two bonds, viz., C(3)7C(4) and C(4)7C( 5), the phototransformation products of cis-caranone (44) only contained compounds formed as a result of the C(4)7C(5) bond cleavage.…”