Photolysis phenyl alkyl ketones

TABLE 12 Product Distribution of Phenyl Alkyl Ketones upon Photolysis in the Presence and Absence of CD ... 

Liberation of excess cyclobutadiene from its iron complex in the presence of acetylenes leads to a double addition, affording the previously unknown tetracyclic system (831 R = Ph or OMe). Trapping with phenyl vinyl ketone affords (832X nhich has been converted by reduction, alkylation, and photolysis into the new tri-cyclo[3,1,1,0 ]heptanols (833). ... 

Alkyl aryl ketone photolysis has been also studied on a silica-gel surface.Molecules in the outermost layer are responsible for the reaction, which has been consequently used for the determination of the solid support surface area. The effect of the alkyl chain length on the type 11 photoreactivity of alkyl phenyl ketones on the surface was found to be insignificant. Based on the quantum yield measurements of valerophenone andp-substituted valerophenone photolysis, a sihca-gel surface was reported to be as strong a polar medium as methanol the surface might cause the inversion of the n,n and n,n triplet states. 

As a consequence of the alignment of solute molecules in liquid-crystalline solvents, the ratio of products formed in competitive reaction pathways can be different from that observed in isotropic liquids. This is illustrated by the Norrish type II photolysis of alkyl phenyl ketones with varying alkyl chain length in the isotropic, smectic, and... 

A condensation of vinyl sulphides of synthetic value involves the reaction of a-ethylthio-styrenes with an aldehyde in the presence of a Lewis acid catalyst to give 3-ethylthio-indenes. Regiospecific and stereospecific pentannelation i.e, fusion of a cyclopentane ring) of an alicyclic ketone involves arylthiomethylen-ation followed by base-catalysed addition to an aj8-unsaturated ester. a-Phenyl-thiobutenolides are less reactive Michael acceptors than their sulphoxide counterparts, and /SjS-dichlorovinyl sulphides are less reactive in electrophilic reactions than their oxygen counterparts. Dimerization of aryl a-cyanovinyl sulphides occurs more readily than that of alkyl analogues, since the intermediate 1,4-diradical ArSC(CN)CH2CH2d(CN)SAr, which cyclizes to the cyclobutane, is more stable. Products obtained by photolysis of methyl vinyl sulphide are accounted for by homolysis of both vinyl—S and methyl—S bonds. The kinetics of catalysed cis-trans isomerization of aryl vinyl sulphides have been studied. ... 

The triplet biradicals c-BRj and c-BRj lead to the stereoisomeric cyclobutanols f-CB and c-CB, respectively, via ISC to the singlet biradicals that have very short Hfetimes. The ratios of trans- to ds-cyclobutanol (t/c) in the type II reaction of alkyl phenyl ketones are in the range from 2 to 5 in nonpolar solvents (Table The ratios become smaller in polar solvents. The tic ratio in the photolysis of... 

Our discussion here focuses on the effects of structure on aliphatic ketones. However, it should be noted that Pitts et al. (1968) determined the effect of the length of the alkyl group (R) on the Norrish type-II process seen in 313 nm photolysis of alkyl phenyl ketones C6HsC(0)R in benzene or hexane solutions. They found (pu decreased from 0.40 for R = n-CaHy to 0.29 for R = n-CgHiy. 

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