Oxiranes photochemical rearrangement

In case of efficient (i.e., proceeding with high quantum yields) and rapid ODPM reactions, the products from photochemical transformations can sometimes not be isolated because of further photochemical transformations. When the epoxyenone 24 is photolysed in acetone in order to generate an oxirane to carbonyl transformation, an appreciable amount of side product 26 was isolated originating from a photochemical rearrangement of the desired reaction product 25 (Sch. 22) [50]. 

Meier and Kolshorn have reported the results obtained from a study of the conversion of oxirens and thiirens to the open-chain isomers. Photochemical rearrangement of the epoxyolefins (279, 280) gives the dihydrofuran derivatives (281, 282). Direct irradiation of the epoxydiene (283) is reported to yield products derived from the fission of the C—C bond of the oxiran (Scheme 18). Other systems studied in this report are the trienes (284) and (285) whose photochemical behaviour is analogous to that reported for (283). Acetone-sensitized irradiation of (283), however, yields products from the fission of a C—O... 

Thermal and Photochemical Reactions of Oxirans. - Isotopic labelling has been used to prove that the thermal rearrangement of phenyloxiran proceeds via a 1,2-shift of hydrogen, and not phenyl migration (Scheme 13). The epoxide (202), labelled with at C-2, gives entirely C(2)-labelled phenyl-ethanol (203) and 3,3- H2-labelled (202) gives (203) with at both C-1 and C-2. The method does not, however, distinguish between the transfer of H and of H. ... 

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