Cyclopropanols and the Di-?-methane Rearrangement: Mechanistic and Exploratory Organic Photochemistry

Article abstract of DOI:10.1021/jo00251a024

The photochemistry of a series of di-?-methane systems, having a hydroxyl group on the methane carbon, was investigated.Both the divinyl and the aryl vinyl versions were studied.In certain cases, an isomeric γ,δ-unsaturated ketone was obtained; the reactant a-b-c-d-e carbon skeletal sequence was permuted to afford the product with the sequence c-a-b-d-e.In two cases intermediate cyclopropanols could be isolated and in all instances evidence was obtained that the bizarre rearrangement resulted from a di-?-methane rearrangement followed by ring opening of the resultant cyclopropanol.Photolysis of the corresponding phenyldimethylsilyl ethers led nicely to the corresponding cyclopropyl ethers in all cases.Tetrabutylammonium fluoride treatment resulted in ring opening.Quantum yields and reaction multiplicites were determined.Direct and sensitized irradiations established both singlet and triplet reactivity.The photochemistry of the cyclopropane products revealed cis-trans isomerization of the silyl ethers and, additionally, ring opening of the cyclopropanols.One of the reactions proved reversible, thus 1,2,2,5,5-pentaphenylpent-4-en-1-one afforded the stereoisomeric 1,2,2-triphenyl-3-<2,2-diphenylvinyl>cyclopropanols.Single photon counting was employed to obtain the excited singlet lifetime and reaction rate for 1,1,3,3-tetraphenyl-2-propen-1-ol.