Acyclic compounds, photochemistry

Discuss photochemistry of carbonyl compounds in cyclic and acyclic compounds. 

In the case of compound 4 photolysis with a medium pressure mercury lamp results in exclusive cleavage of the C—Sn bond fi to the carbonyl group, while the terminal C—Sn bond remains intact. The cyclic ketone 5 and the a, /Lunsaturated ketone 6 are produced in equal if low yields (18%)19. The reduced reactivity of remote C—Sn bonds in such compounds appears to be a general feature of their chemistry, and is also observed in acyclic systems. Thus the photochemistry of organotin compounds with carbonyl groups in the /3-position can be classified as follows ... 

The photochemistry of certain A-substituted heterocycles has also been studied. As part of a continuing investigation of the photolysis of A-nitroso compounds in solution, the conversion of A-nitroso-3-azabicyclo[3.2.2]nonane (65) into the oxime (66) by photolysis in the presence of acid was reported.58 N-Nitrosopyrrolidine is similarly transformed. The mechanism of this reaction is said58 to involve elimination of NOH with the formation of an imine as intermediate, and, in fact, in the photolysis of 2-ethyl-A-nitrosopiperidine (67), the tetrahydropyridine (68) is the major product. This mechanism certainly does not operate in the photolysis of iV-nitroso-2-azacyclo-octanone, which can be rationalized on the basis of an intramolecular hydrogen transfer [Eq. (16)].59 Acyclic iV-nitrosoamides behave in a similar fashion to IV-nitrosoamines.60... 

P,y-Unsaturated aldehydes are a family of carbonyl compounds that have been considered ODPM unreactive for many years. This conclusion was based on literature precedents that indicated that the normal photochemical reactivity of such compounds, both on direct and sensitized irradiation, was decarbonylation to the corresponding alkene. > f> Thus, compounds 5, 6, 7, and 8 are representative examples of a series of steroidal and cyclic P,y-unsaturated aldehydes, studied by Schaffner et al. about 20 years ago, that undergo decarbonylation on irradiation. Diirr et al. have studied the photochemistry of some aryl-substituted-2-cyclopentene-l-carbaldehydes 9. In this instance, ds-stilbene-type electrocy-clic cyclization and decarbonylation were the only reactions observed. Other authors have also reported the decarbonylation of the acyclic P,y-unsaturated aldehydes 10 and 11 on direct irradiation. 

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