Stereochemical control on the photochemistry of α-methoxy-β, γ-cyclopropyl cyclic ketones : reactions of epimeric 3-methoxy-4-caranones

Diarylethene-Based Ionic Liquids: Synthesis and Photo-Driven Solution Properties

“…The possibility of controlling the conductivity of the solutions by UV photoirradiation, can be applied in systems susceptible to these changes, including stereochemistry, [ 51 , 52 , 53 ] polymorphism controllability, [ 54 , 55 , 56 , 57 ] and several other uses in material science, for new innovative materials with specific and/or enhanced properties [ 58 , 59 , 60 ].…”

Skeletal rearrangements of monoterpenoids of the carane series

“…Only its photochemical oxidation to give three hydroperoxides has been reported. 39 Upon irradiation in the presence of a sensitiser, the isomeric 2-carene is rearranged into 1,4,4-trimethylbicyclo[3.2.0]hept-2-ene (32), which has been employed in the synthesis of grandisole. The rearrangement mechanism was not studied in this case; however, the mechanism for a related compound, viz., 2-norcarene (33), has been reported.…”

“…The direction of the skeletal photochemical rearrangement of terpenoids belonging to the carane series depends on the orientation of substituents: direct irradiation of trans-3-methoxy-4caranone (54) in ethanol occurs with opening of the six-membered ring with cleavage of the C(3)7C( 4) bond (which is non-typical of b,g-cyclopropyl ketones) and addition of ethanol. 39 In the case of cis-3-methoxy-4-caranone (55) with an equatorial methoxy group, the only reaction observed is the Norrish type II elimination, resulting in the caranone 44; the required planar six-membered transition state (TS) A is formed readily, and the formation of the ketone 44 competes successfully with the cleavage of the C(3)7C(4) bond. 39 When exposed to light, the ketone 44 undergoes homolytic cleavage of the C(4)7C( 5) bond and homoallylic rearrangement, which is typical of b,g-cyclopropyl ketones.…”

“…39 In the case of cis-3-methoxy-4-caranone (55) with an equatorial methoxy group, the only reaction observed is the Norrish type II elimination, resulting in the caranone 44; the required planar six-membered transition state (TS) A is formed readily, and the formation of the ketone 44 competes successfully with the cleavage of the C(3)7C(4) bond. 39 When exposed to light, the ketone 44 undergoes homolytic cleavage of the C(4)7C( 5) bond and homoallylic rearrangement, which is typical of b,g-cyclopropyl ketones. 44,46 This reaction gives cyclopentanone 56 and cyclobutanone 57.…”