- Chemoenzymatic synthesis of (S)-eicos-(4E)-en-1-yn-3-ol, the cytotoxic principle of the marine sponge, Cribrochalina vasculum
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An efficient enantioselective synthesis of the title compound I was developed from the versatile chiron 1-tert-butyldimethylsilylpenta-1,4-diyn- 3-ol 2. The chiron, in turn, was prepared via a combination of lipase catalyzed acylation-alcoholysis protocol. Protection of its hydroxy group, alkylation with a suitable bromide and subsequent functionalization gave (S)- I with high enantiomeric purity.
- Sharma, Anubha,Chattopadhyay, Subrata
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- Synthesis of [14C] acids from their unlabeled counterparts and application toward a novel [14C] labeled hepatitis C virus polymerase inhibitor
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A strategy has been developed for the rapid construction of a [ 14C] acid from either an aromatic or an alkyl acid via a decarboxylation-carboxylation sequence. A [14C] labeled heptatitis C virus polymerase inhibitor was prepared. Other examples and the limitations of this methodology are discussed. Copyright
- Ho, Jonathan Z.,Wallace, Michael A.,Tang, Yui S.,Zhang, Andy S.,Braun, Matthew P.
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scheme or table
p. 251 - 253
(2011/05/02)
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- Photolytic generation of carbon radicals from Barton esters: Recent developments
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O-Acyl derivatives of N-hydroxy-2-thiopyridone can be photolysed with suitable commercial visible-light lamps to give reactions with very short half-lives (down to 20 s) at 0° C or room temperature.
- Barton,Jaszberenyi,Tang
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p. 3381 - 3384
(2007/10/02)
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- Quantum Yields in the Photochemically Induced Radical Chemistry of Acyl Derivatives of Thiohydroxamic Acids
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Acyl derivatives of N-hydroxyquinazoline-4-thiones are a novel source of disciplined carbon radicals.Quantum yield determination reveals that photolysis of these compounds initiates radical chains, resulting in quantum yields up to φ = 60.Comparative studies with acyl derivatives of N-hydroxy-2-thiopyridone show that the quinazoline derivatives are more light-sensitive than the thiopyridone compounds.The carbon radicals thus formed from the former can be trapped selectively, without the formation of rearranged products (i.e. without the competition of the radicophilic thiocarbonyl group of the starting material with the radical trap).
- Barton, Derek H. R.,Blundell, Paul,Jaszberenyi, Joseph Cs.
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p. 6937 - 6942
(2007/10/02)
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- LIGHT INDUCED HALOGENATIVE DECARBOXYLATION OF THIOHYDROXAMIC ESTERS
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The generality of lidht initiated halogenative decarboxylation of thiohydroxamic esters was studied.This method gave high yields of alkyl chlorides, bromides and iodides derived from primary, secondary and tertiairy substituted carboxylic acids.
- Dauben, William G.,Kowalczyk, Bruce A.,Bridon, Dominique P.
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p. 2461 - 2464
(2007/10/02)
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- The Invention of New Radical Chain Reactions. Part 9. Further Radical Chemistry of Thiohydroxamic Esters; Formation of Carbon-Carbon Bonds
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Carbon radicals derived from the esters of several types of thiohydroxamic acids have been trapped in a number of different ways.Particular attention has been paid to carbon-carbon bond formation by addition to suitably activated ethylenic linkages.Carboxylic acids can be conveniently converted into homo- and bishomo-acids by free radical chemistry based on thiohydroxamic esters.In a coda the tautomerism of the thiohydroxamic acids have been examined by physical methods.It is confirmed that the esters used are derivatives of the thione tautomer.
- Barton, Derek H.R.,Crich, David,Kretzschmar, Gerhard
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- THE INVENTION OF NEW RADICAL CHAIN REACTIONS. PART VIII. RADICAL CHEMISTRY OF THIOHYDROXAMIC ESTERS; A NEW METHOD FOR THE GENERATION OF CARBON RADICALS FROM CARBOXYLIC ACIDS.
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The aliphatic and alicyclic esters of N-hydroxy-pyridine-2-thione are readily reduced by tributylstannane in a radical chain reaction to furnish nor-alkanes.In the absence of the stannane a smooth decarboxylative rearrangement occurs to give 2-substituted thiopyridines.The radicals present in this reaction provoke with t-butylthiol an efficient radical reaction with formation of nor-alkane and 2-pyridyl-t-butyl disulphide.Similarly these carbon radicals can be captured by halogen atom transfer to give noralkyl chlorides, bromides and iodides.With oxygen in the presence of t-butylthiol the corresponding noralkyl hydroperoxides are formed in another radical chain reaction.
- Barton, Derek H. R.,Crich, David,Motherwell, William B.
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p. 3901 - 3924
(2007/10/02)
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- SELECTIVE MIXED COUPLING OF CARBOXYLIC ACIDS (II). -PHOTOLYSIS OF UNSYMMETRICAL DIACYLPEROXIDES WITH ALKENYL-, HALO-, KETO-, CARBOXYL-GROUPS AND A CHIRAL α-CARBON. COMPARISON WITH THE MIXED KOLBE ELECTROLYSIS.
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- Alkenoyl and functionalized alkanoyl dodecanoyl peroxides are prepared in 70 to 97 percent yield and photolyzed at -78 deg C.Thereby 4- to 10-alkenoyl and 4-alkynoyl peroxides afford good yields (56 - 68 percent) of unsymmetrical coupling products.Similarly α- to δ-haloalkanoyl, cholanoyl or 3- and 4-carboxyalkanoyl peroxides can be coupled (40 - 70 percent).The α-chiral diacyl peroxide 1s undergoes the photochemical coupling reaction with 80 percent retention of its configuration.The photolysis of diacyl peroxides at -78 deg C proves to be a favorable supplement of the Kolbe-electrolysis in cases, where the electrolysis fails or produces low yields.
- Feldhues, Michael,Schaefer, Hans J.
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p. 4213 - 4236
(2007/10/02)
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- RADICAL CHEMISTRY OF THIOHYDROXAMIC ACID ESTERS
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Thiohydroxamic esters in general decompose smoothly by a radical chain reaction to give carbon radicals which can be quenched in a synthetically useful manner.
- Barton, Derek H. R.,Kretzschmar, Gerhard
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p. 5889 - 5892
(2007/10/02)
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- A PRACTICAL ALTERNATIVE TO THE HUNSDIECKER REACTION
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Carboxylic acid esters derived from N-hydroxy-pyridine-2-thione react with carbon tetrachloride, bromotrichloromethane or iodoform in a radical chain reaction to give the corresponding noralkyl chlorides, bromides or iodides in high yield.
- Barton, Derek H.R.,Crich, David,Motherwell, William B.
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p. 4979 - 4982
(2007/10/02)
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- Thallium(I) Carboxylate Modification of the Hunsdiecker Reaction
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Treatment of a thallium(I) carboxylate with 1 molar equivalent of bromine gives the corresponding thallium(III) carboxylate dibromide.High yields of primary alkyl bromides are obtained if the thallium(III) carboxylate dibromide is treated with 0.5 mol equiv. of bromine in refluxing carbon tetrachloride.Pyrolysis of the thallium(III) derivative in the absence of added bromine gives a low yield of the corresponding alkyl bromide.The use of thallium(I) carboxylates for the preparation of alkyl bromides in high yields is limited to the salts of primary carboxylic acids.A simple procedure for the preparation of alkyl bromides from carboxylic acids using thallium(I) carbonate has been developed.
- Cambie, Richard C.,Hayward, Rodney C.,Jurlina, Jeffrey L.,Rutledge, Peter S.,Woodgate, Paul D.
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p. 2608 - 2614
(2007/10/02)
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- Vesicant Principles of Poison Ivy and Related Plants: Synthesis of the Urushiols, 1,2-Dihydroxy-3-benzene and 1,2-Dihydroxy-3-pentadecylbenzene
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New syntheses of 1,2-dihydroxy-3-benzene (1) and 1,2-dihydroxy-3-pentadecylbenzene (4), vesicant principles of Poison Ivy (Rhus radicans) and other species of Anacardiaceae, are described starting from 1,2-dimethoxybenzene (7).The lithiation of 1,2-dimethoxybenzene (7) has been re-examined and the yield of the product, 2,3-dimethoxyphenyl-lithium (8), re-determined.The reaction of the aryl-lithium with 1,7-dibromoheptane has been studied by g.l.c., using tributyltin chloride as a quenching reagent.The extracts of two plants of the Anacardiaceae family, Semecarpus vitiensis Engl. and Melanorrhoea beccari Engl., have been examined for the presence of urushiols.The bark of the latter has been found to contain gallic acid.
- Halim, Haroen,Locksley, Harry D.,Memon, Janmohammed J.
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p. 2331 - 2337
(2007/10/02)
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