PHOTOINDUCED ADDITION, OF ALCOHOLS

The photoinduced-addition of alcohols to cycloalkenones has been investigated by Fraser-Reid and co-workers,4 by Paquette,5 and was used as the key step in the synthesis of the prostaglandin endoperoxide analogue (15S)-hydroxy-9a,11a-epoxymethanoprosta-(52,13E)-dienoic acid,6 and for the recent synthesis of 2, 3 -dideoxy-3 -hydroxymethyl-5 -carbanucleosides.7 No work (other than our own) has been reported on the photoinduced-addition of alcohols to 5-substituted furan-2(5H)-ones. 

Decomposition of the photochromic compounds can occur because of the interaction between molecules of the photoinduced form and alcohols. This phenomenon is a consequence of the deficiency of the electron density on the carbon atom in the 9-position of the ana form for aryloxyanthraquinones.27 The reaction of nucleophilic 1,4-addition of alcohol molecules with molecules of 9-aryloxy-l,10-anthraquinones depended on the nature of the substituent.27 The introduction of electron-acceptor substituents enhanced and the electron-donor substituents reduced the rate constant. The electron-donor substituents contributed to the stability of the photoinduced 1,10-anthraquinones. This conclusion was supported by the data on the interaction between derivatives of 9-aryloxy-l, 10-anthraquinone, and aliphatic and aromatic amines.35... 

Although there exist numerous ground state reactions, photochemically induci asymmetric radical additions can be very efficient and even highly stereoselectr [125]. Furthermore, no particular functionalization of the starting material is n< essary prior to the formation of a C-C bond. In this context, the photosensiti addition of alcohols, cyclic acetals, and tertiary amines to electron-deficient kenes has been particularly studied. This will be illustrated by a few exampli First attempts to induce chirality in the photoinduced addition of ket radicals (e.g., U) involved a, 3-usaturated carbonyl compounds such as 208 rived from carbohydrates (Scheme 56) [126]. With benzophenone as sensitizi these radicals could be added stereoselectively, and similar reactions were carri out with dioxolane and a, 3-usaturated nitropyranones [127]. 

Azirines can be transformed to imino esters (259) and (260) (Scheme 37) by addition of alcohols or alkoxy carbenes respectively. By sodium methoxide catalyzed addition of methanol to the ketene imine (261 Scheme 38) the imino ester (262) is obtainable. Keteneimines undergo photoinduced addi-... 

Alternatively, these heterocycles (e.g., 157) can be prepared by the reaction of dimethyl-(chloromethyl)allylsilane (156) with alcoholic KSH (Equation (30)) <83J0M(243)271, 83ZOB2404>. A similar cyclization can be effected by the photoinduced addition of H2S to the vinyl congener of (156) <82ZOB712>. 

The photoinduced anti-Markovnikov addition of methanol to 1,1-diphenylethene reported by Arnold and co-workers in 1973 provides the first example of the addition of a nucleophile to an arylalkene radical cation. There are now a number of studies that demonstrate the generality of nucleophilic addition of alcohols, amines, and anions such as cyanide to aryl- and diaryl-alkene radical cations. Product studies and mechanistic work have established that addition occurs at the 3-position of I-aryl or 1,1 -diarylalkene radical cations to give arylmethyl or diaryl-methyl radical-derived products as shown in Scheme I for the addition of methanol to 1,1-diphenylethene. For neutral nucleophiles, such as alcohols and amines, radical formation requires prior deprotonation of the 1,3-distonic radical cation formed in the initial addition reaction. The final product usually results from reduction of the radical by the sensitizer radical anion to give an anion that is then protonated, although other radical... 

It is interesting to note that the photoinduced reactions of closely related compounds such as the dimethiodide of trans-l,2-bis(4-pyridyl)ethylene [59], while appearing to involve initial electron transfer processes, give high yields of products arising from addition of water, alcohols, ethers etc. at the double bond as in (189) for... 

The overall reaction is currently regarded as an apparent hydride transfer (for review, see ) because a) hydrogen is transferred directly between the reactants in most cases, without exchange with the solvent, 2) the base-catalyzed disproportionation of benzaldehyde to benzyl alcohol and benzoic acid (Cannizzaro reaction) i ems to be a hydride transfer (3) stereospecificity can be observed in model reactions. In addition, Verhoeven and coworkers have analyzed the thermodynamics of the photoinduced reaction between l-benzyl-3-carbamido-l,4-dihydropyridine and l,l-dimethyl-4,4 -bipyridylium dication, and have concluded that a thermal 1 e reaction between a 1-alkyl-1,4-dihydronicotinamide and a carbonyl compound is unlikely. 

Oxidative functionalization of alkenes. Activated by cerium(IV) ammonium nitrate in methanol Ph2Se2 initiates addition to an alkene. Some unsaturated alcohols undergo phenylselenocycloetherification, and in case that the activation is by a photoinduced electron transfer process the phenylseleno group of the products can be replaced. 

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