The photochemistry of 2,4- and 2,6-cyclo-octadienone

[摘要] Medium-ring unsaturated ketones have been found to undergo several types of photochemical reactions, including cis-trans isomerization of double bonds, rearrangements, and bridging to bicyclic products. In several instances strained products with trans double bonds undergo further thermal reactions. The present investigation dealt with the photochemistry of 2,4-cyclooctadienone and 2,6-cyclooctadienone. Irradiation of 2,6-cyclooctadienone in inert solvents gave tricyclo [3.2.1.04,7] octan-8-one. This compound was conclusively identified by a cleavage reaction to endo-6-carbomethoxy-bicyclo [3.2.0] heptane. The reduction product of this molecule was identified by comparison of its infrared spectrum to the infrared spectrum of an authentic sample prepared by an unambiguous route. In methanol and furan, however, capture of a reactive intermediate in the photolysis occurred much more rapidly than intramolecular rearrangement. This reactive intermediate was detected by using low temperature photolysis techniques to involve a strained ground state trans intermediate. Irradiation of 2,4-cyclooctadienone produced a dimer resulting from self addition across the c68-double bonds of two molecules of the dienone. The, exact configuration of the dimer at the cyclobutane ring has not yet been determined. Photolysis in methanol and furan also gave products in which the elements of methanol or furan had been added to the dienone. Low temperature photolysis techniques also showed that this molecule was photochemical isomerized to trans-cis-2,4-cyclooctadienone and that subsequent thermal reaction with the nucleophile produced the observed products.

[发布机构] Rice University