- Regioselective silver-mediated Kondakov-Darzens olefin acylation
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Enone construction: A silver-mediated olefin acylation reaction is described, in which five-, six-, and -seven-membered rings, tetrasubstituted olefins, bridged bicycles, spirocycles, and benzoxepinones are prepared. Highly selective intermolecular reactions are coupled to a Nazarov cyclization for the effective preparation of cyclopentenones, including the core of modhephene (see scheme). Copyright
- Barczak, Nicholas T.,Jarvo, Elizabeth R.
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p. 12912 - 12916
(2011/12/04)
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- Lipase-catalyzed resolution of p-menthan-3-ols monoterpenes: Preparation of the enantiomer-enriched forms of menthol, isopulegol, trans- and cis-piperitol, and cis-isopiperitenol
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A study on the enzymic resolution of the most common p-menthan-3-ol monoterpene isomers is described. Enantioenriched alcohols 1, 5, 10, 11 and 12 are obtained by means of the lipase-mediated kinetic acetylation of the corresponding racemic materials. The stereochemical aspects of the enzymic process have been investigated. We found that the structural features of the starting p-menthan-3-ol as well as the kind of lipase used, impacted strongly on the enantioselectivity of the resolution. The potentialities of this approach for preparative purposes are discussed.
- Serra, Stefano,Brenna, Elisabetta,Fuganti, Claudio,Maggioni, Francesco
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p. 3313 - 3319
(2007/10/03)
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- An efficient procedure for the preparation of (E)-α-alkylidenecycloalkanones mediated by a CeCl3·7H2O-NaI system. Novel methodology for the synthesis of (S)-(-)-pulegone
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2-Alkylidenecycloalkanones are powerful synthons used as the key intermediates in many important syntheses. Because of their potential, a general method of preparation from readily available starting materials, under very mild conditions, was considered to be worthwhile. Cerium(III) chloride heptahydrate in combination with sodium iodide in refluxing acetonitrile promotes a regio- and stereoselective β-elimination reaction to (E)-2-alkylidenecycloalkanones in 2-(1-hydroxyalkyl)cycloalkanones. The synthetic value of the present procedure is demonstrated by the synthesis of monoterpene (S)-(-)-pulegone (8) in its optically active form.
- Bartoli, Giuseppe,Bosco, Marcella,Dalpozzo, Renato,Giuliani, Arianna,Marcantoni, Enrico,Mecozzi, Tiziana,Sambri, Letizia,Torregiani, Elisabetta
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p. 9111 - 9114
(2007/10/03)
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- A versatile cobalt(II)-Schiff base catalyzed oxidation of organic substrates with dioxygen: Scope and mechanism
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Cobalt(II) complex 1a-f derived from Schiff bases act as efficient catalysts during the oxidation of wide range of organic substrates(e.g. alkenes, alcohols, benzylic compounds and aliphatic hydrocarbons) with dioxygen in the presence of aliphatic aldehydes or ketones or ketoesters. EPR studies on 1a-f complexes suggest that the aliphatic carbonyl compounds promote the formation of a cobalt(II)-superoxo species responsible for the oxidation of organic compounds. These studies also demonstrate the role of ligands on cobalt in controlling the chemoselectivity of these oxidations. A plausible mechanistic rational is also provided for these oxidations.
- Punniyamurthy,Bhatia, Beena,Reddy, M. Madhava,Maikap, Golak C.,Iqbal, Javed
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p. 7649 - 7670
(2007/10/03)
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- Regio- and enantio-selective enolisations of cyclic ketones using chiral lithium amide bases
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Enolisations of 3-methylcyclohexanone 16, and of a trans-fused perhydroisoquinolone derivative 8, using several chiral lithium amide bases have been examined.In reactions involving a single enantiomer of the ketone 8, the use of a chiral base can result in enhancement or reversal of the normal regioselectivity of enolisation to give the enol silane derivatives 9 and 10, depending on the configuration of the base used.Similar matched and mismatched results are observed when (R)-3-methylcyclohexanone, (R)-16, is treated with either enantiomer of the chiral base 3.A new type of kinetic resolution, termed regiodivergent resolution, is observed when enolisation of the racemic ketones 8 or 16 is carried out using the chiral base 3.
- Bambridge, Kimberley,Clark, Barry P.,Simpkins, Nigel S.
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p. 2535 - 2542
(2007/10/02)
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- Cobalt catalyzed oxidation of secondary alcohols with dioxygen in the presence of 2-methylpropanal
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Cobalt schiff base complex 2 catalyses the oxidation of a wide range of secondary alcohols to the corresponding ketones in the presence of dioxygen and 2-methylpropanal.
- Kalra, Swinder Jeet Singh,Punniyamurthy,Iqbal, Javed
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p. 4847 - 4850
(2007/10/02)
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- Cobalt(II) Schiffs base complex catalysed oxidation of alcohols with dioxygen in the presence of ethyl 2-oxocyclopentanecarboxylate
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Cobalt(II) Schiffs base complex 1 catalyses the oxidation of primary and secondary alcohols to aldehydes and ketones respectively, in the presence of dioxygen and ethyl 2-oxocyclopentanecarboxylate 2 at 60-70° C.
- Punniyamurthy,Iqbal, Javed
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p. 4007 - 4010
(2007/10/02)
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- Potassium Chlorochromate on a Solid Support: A Convenient and Mild Reagent for the Oxidation of Alcohols
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The oxidation of primary and secondary alcohols by potassium chlorochromate supported on alumina or silica gel is reported.The results indicate that the yields in some cases depend on the support medium.Benzylic and secondary alcohols are oxidized in the best yields.The effect of solvent on the reaction is discussed and the conclusion is drawn that the best yields are obtained in non-polar solvents.
- Carlsen, Per H. J.,Husbyn, Mette,Braenden, Jon E,,Eliason, Robert
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p. 485 - 488
(2007/10/02)
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- Oxidation of Alcohols with Potassium Chlorochromate
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Potassium chlorochromate, KCrClO3, (KCC) is a versatile and inexpensive oxidation reagent.It converts secondary saturated, as well as allylic and benzylic alcohols to the corresponding carbonyl compounds in high yields in a variety of solvents, preferentially acetone.The reagent is highly selective.Thus, oxidation of primary alcohols gives aldehydes as the exclusive products.KCC is less useful for the transformation of primary saturated and homoallylic alcohols.Double bonds are susceptible to isomerization under the reaction conditions employed; for example, oxidati on of pure nerol yields citral, and pulegol is converted to a mixture of pulegone and isopulegone.Oxidation of tertiary allylic alcohols may give the transposed aldehyde.Thus, linalool is converted to citral in high yield.
- Carlsen, Per H.J.,Braenden, Jon Eric
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p. 313 - 317
(2007/10/02)
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- A MILD HYDROGENOLYTIC-HYDROLYTIC CONVERSION OF OXIMES TO CARBONYL COMPOUNDS.
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Oximes are converted into the corresponding carbonyl compounds in high yields using Raney-nickel and sodium hypophosphite at pH 5.
- Monti, D.,Gramatica, P.,Speranza, G.,Tagliapietra, S.,Manitto, P.
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p. 803 - 808
(2007/10/02)
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- PALLADIUM CATALYZED OXIDATION OF Δ2, Δ3, AND Δ4-UNSATURATED ALCOHOLS
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Palladium (0.63 molpercent) catalyzes the oxidation of Δ2, Δ3, and Δ4-unsaturated alcohols to the corresponding ketones in good yields, where bromomesitylene or bromobenzene is used as an oxidant.
- Tamaru, Yoshinao,Inoue, Kenji,Yamada, Yoshimi,Yoshida, Zen-ichi
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p. 1801 - 1802
(2007/10/02)
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- A NOVEL METHOD FOR THE TERPENE SYNTHESIS BY THE RING-OPENING REACTION OF β-METHYL-β-PROPIOLACTONE
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A new route for the terpene synthesis is investigated, which undergoes via terpene carboxylic acids as key intermediates obtained by the regiospecific ring opening of β-methyl-β-propiolactone with cuprate or with a Grignard reagent in the presence of a copper catalyst.
- Fujisawa, Tamotsu,Sato, Toshio,Kawara, Tatsuo,Noda, Atsunari,Obinata,Toshiyuki
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p. 2553 - 2554
(2007/10/02)
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