Unusual Photoaddition

Sensitized photoaddition of singlet oxygen to 3,5-di-r-butyl-1 -ethoxycarbonyl-1//-azepine, which is known to give a [6+2]ir adduct with TONE, was also investigated. However, in this instance only the [4+2]ir adduct (162 R = Bu ) is isolated, which on heating at 170 °C undergoes an unusual rearrangement to the epoxy-epioxide (165) in 95% yield. 

The photodecomposition of oxiran and alkyloxirans both in the gas phase and in solution has been extensively investigated. Processes arising by carbon-oxygen bond homolysis and hydrogen abstraction have been reported, and the subject has been reviewed in detail elsewhere.48 The most recent studies include the photoaddition of methanol to alicyclic epoxides, a process that appears to be promoted by acid,49 and the interesting if unusual photochemically induced conversion of the epoxyalcohol (56) to sugiresinol dimethyl ether (57).50... 

Figure 8.18 Unusual [2+2] photoadditions of maleimide (23) and pyrene (22) or fluoranthene (25) within cage 2.

Photoaddition reactions of azo compounds and photochemical para additions to benzenes are both rare so formation of the adduct (28) from N-methyltriazolinedione and benzene is an unusual process on bodi counts (Hamrock and Sheridan). In the meta-cvcloaddition of alkenes to benzenes, there are both theoretical and experimental grounds for believing that the Si benzene undergoes... 

Oxetans. - A mechanistic investigation of the reaction of methylthiotri-methylsilane (38) and oxetan, in the presence of a catalytic amount of zinc chloride, suggests the involvement of an oxonium cation-methylthiozinc dichloride ion-pair, resulting in the formation of (3-methylthiopropoxy)-trimethylsilane (39). A dependence of the stereochemistry of the photoaddition products of aldehydes and alkenes on the concentration of alkene has been observed.Additional examples of the known photo-addition of benzophenone to 2,5-dimethylthiophen to form an oxetan have been reported and the unusual bis(cyanomethylene)oxetan (40) has been described. ... 

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