Alkenes irradiation

R Molar Ratio of 8 to Alkene Irradiation Time (h) Total Dosage (r. X 10 ) Yield (%) of 1 1 Adduct... 

Chloro(methoxy)- and chloro(phenoxy)carbenes, which are generated from the diazirine precursors, behave as ambiphiles in additions to alkenes, exhibiting high reactivities toward both electron-poor and electron-rich olefins. Methoxy(phenyl)- and ferrocenyl(methoxy)methylenes have been transferred in a stereospecific manner from transition metal complexes of these species to electron-deficient alkenes. Irradiation of benzocyclobutanedione with UV light induces a rearrangement of the cyclic a-diketone to 17, which has been trapped by alkenes in good yields " . Thermolysis of 18 gives rise to nucleophilic dimethoxycarbene, which has been intercepted by electron-deficient olefins or by styrene derivatives. 

Methylenecyclopropane undergoes photosensitized [2 + 2] cycloaddition with various substituted alkenes. Irradiation of acetone solutions of maleic anhydride or substituted derivatives and methylenecyclopropane in the presence of benzophenone as a sensitizer gave spiro[2.3]hexa-nes 24 in good yields. 

Dimethyl-4//-l,3-dioxin-4-one 139 has been used as the photochemical equivalent of formylacetate, which is inactive as the enone partner in the photoaddition with alkenes. Irradiation of dioxinone 139 in the presence of symmetrical cyclopentene 140 leads to the cyclobutane adduct 141. This intermediate upon subjection to hot water undergoes retro-aldol fragmentation and spontaneous lactonization to give lactone 143, a useful prostaglandin intermediate. Enantiomerically pure lactone 143 is prepared by using a chiral version of dioxinone 139. ... 

The photochemistry of the complexes Fe(CO)4(alkene) have received considerable attention. The complexes show an absorption band between 250 nm and 290 nm (e = 4500-9500) that has been assigned to an MLCT transition to the coordinated alkene. " Irradiation of Fe(CO)4(dimethyl maleate) leads to both photoexchange of the coordinated dimethyl maleate with isotopically labeled dimethyl maleate, and to cis trans isomerization of the coordinated alkene ... 

Also quite recently, Yoshizawa et al. found that self-assembled coordination cages containing palladium can function as a medium of dimerization of alkenes. Irradiation of ACN or 1-methyl-ACN (23) in coordination cages in DjO resulted in efficient formation of the dimers with high stereoselectivity and regioselectivity with a preference for cisoid-l of > 49 (ACN) and the anti-cisoid-diraer of > 49 (23), which is in contrast with the less efficient reaction in benzene with the ratio of 1.1 (ACN) and no reactivity (23) (Scheme 10). 

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