Rearrangement enone—benzene

The enone epoxide (169) is photochemical ly reactive and on irradiation in benzene solution afforded the six products shown in Scheme 7. The formation of products involves the photochemical formation of two intermediates (170) and (171). These thermally rearrange to the observed products with the intermediate (169) yielding (172 - 175) while intermediate (171) affords the furan (176). The complexity of these reaction paths is to be contrasted with the simpler reaction path described earlier by Mukai et aJ. ... 

The cyclohexenone (212) is photochemically reactive in methanol and affords the bicyclic derivative (213) by a 1,2-phenyl migration in a di-m-methane rearrangement. This is accompanied by and the cyclohexenone (214) presumably formed by a reduction-elimination pathway. Change of solvent to benzene afforded only bicyclic compound (213).t three enones (215) undergo photo-rearrangement to the two products (216) and (217). The reaction appears to be solvent independent in that the same rearrangement products are obtained in benzene, t-butanol, or acetonitrile. The first compound (215, R=CF ) does behave differently in t-butanol and acetonitrile in that the rearrangement is accompanied by the cycloalkanone (218). ... 

Intermolecular.- cis-trans-Isomerization of the enone (31) occurs on irradiation and this is followed by formation of the adducts (32) and (33) by a thermal cycloaddition of the trans-isomer of (31) to a ground state cis-isomer. Such a mechanism involving cis-frans-isomerization is supported by the fact that the reaction does not show a solvent dependency and can be brought about equally efficiently in t-butanol or benzene.The enone 31) does not undergo 1,2-phenyl migrations of the type associated with the di-Tc-methane rearrangement of 4,4-diphenyl eye 1 ohexenone derivatives. The regiospecific... 

The reactions of the /fy-enones (115) and (116) have provided a useful route for the synthesis of 1,4-diketones.85 The irradiation of (115) in degassed benzene affords hexane-2,5-dione (35%) by a 1,3-acyl shift, probably from the singlet state (the reaction could not be sensitized or quenched). However, rearrangement of the enone (116) to 3-acetylcyclohexanone (22%) under the same conditions... 

Njardarson and coworkers utilized the Cu-catalyzed ring expansion of thiiranes developed in their lab as the key step in syntheses of the cores of Biotin and Plavix tSchemes 11.62 and 11.63). The vinylthiirane precursor 102 for Biotin s core was prepared by cross metathesis of ethyl 6-heptenoate 100 with enone thiophosphate 101, followed by selective reduction using NaBH4 and subsequent cyclization (Scheme 11.61T Rearrangement of 102 using 5 mol% Cu(hfacac)2 in benzene afforded dihydrothiophene 103 in high yield and can be converted to Biotin in a few steps tScheme 11.62T ... 

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