Cyclopentanone ring, 3-hydroxy

Asymmetric ring opening of 3,4-epoxy cyclopentanone (desymmetrization) catalyzed by 2 mol% of an (R)-BINOL modified aluminum complex affords the (4/ )-hydroxy enone in 95% ee at 98% yield (Scheme 7-29).2... 

A similar example is the ring expansion of cyclobutanone via l-tris(methylsulfanyl)methyl-cyclobutanol (6) to 2,2-bis(methylsulfanyl)cyclopentanone (7).43 The use of Af,A-diisopropyl-ethylamine is unneccessary in this reaction as the hydroxy group has already been deprotonated with butyllithium. Further examples of this type of reaction can be found in refs 43 and 44. 

In contrast, when the X group is oxygen, the reaction appears to follow the cationic alkene cylization-pinacol-like rearrangement pathway. In this case, reaction of an optically pure acyclic oxygen-containing analog of the system in Scheme 71 leads to a product with preservation of optical activity.This reaction protocol, which accomplishes an overall ring expansion with a tetrahydrofiiran annulation, has been examined for ot-hydroxy-cyclopentanones and -cyclohexanones (Scheme 73 and equations 29-31). ... 

The regioselective synthesis of the unnatural cuparenone isomer (C, Scheme 98) has also been performed 135) (Scheme 98b) from the same oxaspirohexane by a two-steps sequence which involves the selective (100%) — opening of the epoxide ring leading to the corresponding 1-(1-hydroxy)-l-(chloromethyl)cyclobutane (BeCl2/ THF, 20 °C, 20 hr) and its further transformation to the cyclopentanone C is achieved 13S) with silver tetrafluoroborate on alumina. 

Subsequent work has shown that the presence of an alkyl substituent a to the ketone carbonyl is crucial for the intramolecular five-membered-ring cyclization to occur. Thus, jS-hydroxy cyclopentanones can be synthesized from ketones containing both methyl and cyclopropanol moieties a to the carbonyl by treatment with sodium hydride at 0-25 °C. In the case of phenyl ketone, further retro-aldol ring scission leads to the 1,4-diketone as the only product. A retro-aldol/re-aldol sequence occurs when the methyl substituent is replaced by a longer alkyl substituent, such as an allyl group. In this case, the allyl substituent is located 7 to the carbonyl of the final product. ... 

Oxidation of cammaconine with Sarett reagent afforded two products, dehydro-oxocammaconine (23) and didehydro-oxocammaconine (24). Both products showed spectral characteristics for two methoxy-groups, an AT-ethyl group, a hydroxy-group, a cyclopentanone moiety, and a tertiary lactam in a six-membered ring. The second product also possessed an i.r. absorption band characteristic of a cyclohexanone. There was no evidence of an aldehyde proton in the n.m.r. spectra of either product. 

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. ... 

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