Epoxy ketone photolysis

Pyrolysis, photolysis, and electronolysis of ethylene oxide (128) yielded similar products (P. Brown et al., 1966). Electron impact-induced fragmentation (129) of the epoxide (51) (P. Brown et al., 1966) was similar to the photochemical behaviour (130) of the epoxide (52) (Kristinsson and Griffin, 1966). Rearrangement of the a,/3-epoxy-ketone to the diketone after ionization (131) has been suggested to account for... 

Carbon-oxygen bond heterolysis is responsible for the observed photolyses of 9-aryl-9-xanthenols ° and llH-benzo[b]fluoren-11-ol. - - Evidence for the formation of the 9-fluorenol radical cation as well as the 9-fluorenyl cation has been obtained from a laser flash photolysis study of 9-fluorenol. 1, l-Di-2-thienylethanol undergoes light-induced dehydration to give i,i-di-2-thienylethylene.Single electron transfer pathways, however, are implicated in the ring cleavage reactions of a,j8-epoxy ketones in the presence of allyltributyltin - or alkylamines. 

Photolysis of a-epoxy-ketones that are excited in their triplet states leads to jS-diketones, a-diketones, or fragmentation products. The reaction pathway depends on the localization of energy for the system thus (219 Ar = Ri, Ar = 1-naphthyl), on irradiation at 366 nm, at room temperature, in MeCN, gave naphthaldehyde (75%) and the a-diketone (220) (8%) whereas (219 Ar = 2-naphthyl, Ar =Ph), under the same conditions, gave (221) (66%). The absorption spectra of the ylide intermediates in these reactions were reported. o... 

P-Hydroxy ketones from a.P-epoxy ketones. 5 The conversion can be effected by photolysis with Bu.iSnH or by a thermal reaction (98°) with BujSnH/AIBN in Qll. The former reaction is particularly useful for aroyl-substitutcd epoxy ketones. 

Photo-oxygenation of cyclohepta-3,5-dienone that is sensitized with tetra-phenylporphyrin leads initially to the 3,6-endoperoxide this, on reduction with di-imide, gives (5), from which (6) and (7) were obtained, via photolysis at 300 nm in CDCI3 and subsequent deoxygenation with PPhs in CH2CI2, at 0 °C, respectively. Photo-oxidation of 3-methylfuran in CH2CI2 at 0 °C, with methylene blue as the sensitizer, led directly to the epoxy-ketones (8) and (9), together with some diepoxide. 

Irradiation of 2,5-dimethylbenzoyl oxiranes results in formation of p-hydroxy functionalized indanones (74) that structurally resemble biologically active pterosines. Nanosecond laser flash photolysis and quantum-chemical calculations based on density functional theory support a photoenolization mechanism.Reversible photochemical transformations of cis- and tra v-2,3-dimethyloxirane radical cations in freonic matrices at 77 K has been observed and explained by the interconversion between the open (C2-C3 broken) and the cyclic forms. Photocatalytic ring opening of a-epoxy ketones in cyclopentanone, using 2,4,6-triphenylpyrylium tetra-fluoroborate as electron acceptor, results in the diastereoselective formation of 2,5-dioxaspiro[4,4]nonanes through Ca-O bond cleavage and subsequent nucleophilic attack by cyclopentanone to the radical cation intermediates. ... 

Photolysis of epoxy ketone 54, obtained upon oxidation of unsaturated ketone 53 with m-chloroperbenzoic acid (MCPBA) in dry benzene, afforded the aldehydoketene 55. The ketene cis-55, firstly undergoes photochemical isomerization to the trans-isomer on prolonged irradiation, and then undergoes an intramolecular [4 - - 2] cycloaddition on heating to afford the bicyclic lactone 56 (Scheme 19) (1978JOC3314). 

Ring Retention. Whereas the photochemistry of a,/S-epoxy-ketones has been investigated in depth, the behaviour of, y-epoxy-ketones has previously been neglected. Photolysis of the steroidal /S,y-epoxy-ketone (470) results in... 

Carbonyl Compounds.—Photolysis of the l-en-19-al (509) afforded 19-nor-5a-cholest-l-ene (510). The 2a,5a-epoxy- and 2a,5a-epithio-3-ketones (511) were... 

Acetates or benzoates of saturated or A - or A -unsaturated 3)3-hydroxy-steroids are deoxygenated by photolysis in hexamethylphosphotriamide. Photochemical rearrangements of the 4,5-epoxy-6-ketone (758) and 5,6-epoxy-... 

Oxiranecarboxylic acids 41 (glycidic acids) can be converted into a,P epoxy diazomethyl ketones 42 via mixed anhydrides. It was found that photolysis of these compounds in the presence of alcohols gave yhyunsaturated esters 44. It is thought that nucleophilic attack of the alcohol on the ketene 43 results in epoxide ring opening. The E olefin isomer is predominately formed, although small quantities of Z esters are also isolated (< 10%). Conveniently non-racemic, chiral substrates are readily prepared via Sharpless asymmetric epoxidation of allylic alcohol 39, followed by... 

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