Photochemistry of Alkenes, Alkynes, and Related

Addition Beactions.- The photohydration of substituted styrenes and phenyl acetylenes has been studied in acid nediun. - Diyne (1) is also photochenically reactivetirradiation at 300 nm) with methanol affording the addition product (2) as a mixture of Z and E isomers. The isomeric products (2) are photochemically labile and are interconverted on prolonged irradiation affordina a photostationary mixture.  

Mariano and his coworkers have continued their study of the photoreactions of iminlua salts. Thus the xanthone-sensitized irradiation of the pyrrolinium perchlorates (10) brings about cyclization yielding the products (11).  

Physical details relating to the isomerization of the stilbenes (12) have been determined.A study of the photophysical properties of the styrylstiIbenes (13) has shown that quantum yields for trans-cis isomerism are low from the singlet but high from the triplet state. The photochemical isomerization of the alkene (14) in an ethanol glass affords the trans-isomer with high efficiency even at liquid helium temperatures. Photochemical cis-trans-isomerization of cis-1,2-di-l-naphthylethylene (14) has also been studied in the crystalline phase. A study of the photochemical isomerization of a series of styryl phenanthrenes has been reported. The mechanism of the reaction involved was discussed.  

An investigation of the photochemical behaviour of the dianthryl ethylenes (15, 16) has been carried out. Irradiation of the Z-isomer (15) brings about the formation of the (4+4)-addition product (17) with a quantum yield of 0.16. Irradiation of the -isomer (16a) also affords this cycloaddition product (17) but because of the need for prior frans-cis-isomerization the overall quantum yield, 0.002, is much lower. The irradiation of the enol (16b) follows a different route and yields (18) following an intramolecular hydrogen transfer process. 

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IIH3 Photochemistry of Alkenes, Alkynes and Related Compounds... 

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