- Amine Catalysis for the Organocatalytic Diboration of Challenging Alkenes
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The generation of in situ sp2–sp3diboron adducts has revolutionised the synthesis of organoboranes. Organocatalytic diboration reactions have represented a milestone in terms of unpredictable reactivity of these adducts. However, current methodologies have limitations in terms of substrate scope, selectivity and functional group tolerance. Here a new methodology based on the use of simple amines as catalyst is reported. This methodology provides a completely selective transformation overcoming current substrate scope and functional/protecting group limitations. Mechanistic studies have been included in this report.
- Farre, Albert,Soares, Kaline,Briggs, Rachel A.,Balanta, Angelica,Benoit, David M.,Bonet, Amadeu
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p. 17552 - 17556
(2016/11/28)
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- Asymmetric synthesis of α-methyl-α-amino acids via diastereoselective alkylation of (1s)-(+)-3-carene derived tricyclic iminolactone
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A novel carene-based alanine-equivalent tricyclic iminolactone 16 has been synthesized via stereoselective dihydroxylation of the double bond, IBX oxidation of the secondary alcohol, esterification of the tertiary alcohol, deprotection of the resulting ester, and subsequent cyclization from commercially available (1S)-(+)-3-carene in 79% overall yield. The iminolactone 16 demonstrated high reactivity toward alkylation with a wide range of electrophiles at room temperature under phasetransfer catalysis conditions. The alkylated products were produced with excellent diastereoselectivities (>98% de) in good isolated yields (86-94%). High yields (83-91%) of optically pure (S)-R-methyl-R-substituted-R-amino acids were obtained by basic hydrolysis of the dialkylated iminolactones with the recovery of the chiral auxiliary 15 (78-87%).
- Lu, Ta-Jung,Lin, Cheng-Kun
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experimental part
p. 1621 - 1633
(2011/06/17)
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- Thiol-catalysed radical-chain redox rearrangement reactions of benzylidene acetals derived from terpenoid diols
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The thiol-catalysed radical-chain redox rearrangement of cyclic benzylidene acetals derived from 1,2- and 1,3-diols of terpene origin has been investigated from both synthetic and mechanistic standpoints. The redox rearrangement was carried out either at ca. 70°C (using ButON=NOBut as initiator) or at ca. 130°C (using ButOOBut as initiator) in the presence of triisopropylsilanethiol or methyl thioglycolate as catalyst; the silanethiol was usually more effective. This general reaction affords the benzoate ester of the monodeoxygenated diol, unless rearrangement of intermediate carbon-centred radicals takes place prior to final trapping by the thiol to give the product, in which case structurally rearranged esters are obtained. For the benzylidene acetals of 1,2-diols prepared by vicinal ds-dihydroxylation of 2-carene, α-pinene or β-pinene, intermediate cyclopropylcarbinyl or cyclobutylcarbinyl radicals are involved and ring opening of these leads ultimately to unsaturated monocyclic benzoates. 1,2-Migration of the benzoate group in the intermediate p-benzoyloxyalkyl radical sometimes also competes with thiol trapping during the redox rearrangement of benzylidene acetals derived from 1,2-diols. Redox rearrangement of the benzylidene acetal from carane-3,4-diol, obtained by cis-dihydroxylation of 3-carene, does not involve intermediate cyclopropylcarbinyl radicals and leads to benzoate ester in which the bicyclic carane skeleton is retained. The inefficient redox rearrangement of the relatively rigid benzylidene acetal from exo,exo-norbornane-2,3-diol is attributed to comparatively slow chain-propagating β-scission of the intermediate 2-phenyl-1,3-dioxolan-2-yl radical, probably caused by the development of adverse angle strain in the transition state for this cleavage. Similar angle strain effects are thought to influence the regioselectivities of redox rearrangement of bicyclic [4.4.0]benzylidene acetals resulting from selected 1,3-diols, themselves prepared by reduction of aldol adducts derived from reactions of aldehydes with the kinetic lithium enolates obtained from menthone and from isomenthone.
- Dang, Hai-Shan,Roberts, Brian P.,Tocher, Derek A.
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p. 4073 - 4084
(2007/10/03)
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- Reactions of cis-and trans-epoxy derivatives of (+)-3-carene and limonene with aldehydes over askanite-bentonite clay
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cis-and trans-Epoxy derivatives of (+)-3-carene, limonene, and dipentene react with aldehydes in the presence of askanite-bentonite clay to give acetals. Hydrolysis of the latter selectively yields the corresponding cis-diols. The relative contribution of intra-and intermolecular processes in the reactions of epoxy derivatives with aldehydes is determined mainly by steric factor. * This study was financially supported by the Russian Foundation for Basic Research (project no. 97-03-32 952a).
- Volcho,Tatarova,Korchagina,Salakhutdinov,Barkhash
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- Rhutenium-Catalyzed cis-Dihydroxylation of Alkenes: Scope and Limitations
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Oxidative ruthenium catalysis (0.07 molequiv RuCl3*(H2O)3, 1.5 molequiv NaIO4, EtOAc/CH3CN/H2O 3:3:1), beyond the usual C-C bond cleavage to give dicarbonyls, have been shown to syn-dihydroxylate a wide range of alkenes (except for strained bicyclic alkenes, sterically hindered trisubstituted alkenes, and most tetrasubstituted alkenes) to give vicinal diols rapidly (within minutes) and efficiently.The minor products are the usual oxidative fission products, namely, ketones and aldehydes or carboxylic acids, and sometimes ketols.Longer reaction times lower the yields of most diols, probably owing to oxidative glycol cleavage.Reactions with substrates containing one or more electron-withdrawing groups in conjugation with or adjacent to the alkene moiety are generally slower but give better yields.The diastereoselectivity of the present "flash" dihydroxylation, anti to the existing α-stereogenic center, with cycloalkenes is excellent whereas that with acyclic alkenes is moderate to poor.Sodium metaperiodate is still the best co-oxidant for the catalytic reaction.Aqueous acetonitrile (approximately 86percent) as an alternative solvent system was found to give better yields of 1,2-diols than the original solvent system in some cases. - Keywords: alkenes, catalysis, dihydroxylations, electrophilicity, ruthenium compounds.
- Shing, Tony K. M.,Tam, Eric K. W.,Tai, Vincent W.-F.,Chung, Ivan H. F.,Jiang, Qin
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- Monoterpenediol insect repellents
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An insect repellent comprising as an active ingredient a monoterpenediol compound having the formula, STR1 wherein R1, R2 and R3 have either one of the following definitions: (i) all of R1, R2 and R3 are hydrogen, (ii) R1 is hydrogen and R2 and R3, taken together, form a carbon-carbon single bond, or (iii) R2 is hydrogen, R1 and R3, taken together, form a carbon-carbon single bond, and the hydroxyl bonded to the carbon atom marked with an asterisk takes an α-configuration.
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- ONE-POT TWO-STEP SYNTHESIS OF 1,2-DIOL
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Diols can be prepared by hydroxilation of alkenes with m-chloroperoxybenzoic acid in water.The process occurs with high yield and complete anti stereospecificity.
- Fringuelli, F.,Germani, R.,Pizzo, F.,Savelli, G.
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p. 1939 - 1944
(2007/10/02)
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- Transformations of 3-carene oxide at rhenium-containing catalysts
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The transformations of 3-carene oxide at rhenium-containing catalysts were studied.The introduction of rhenium into the catalytic system significantly increases the reaction rate and leads to the formation of compounds not previously encountered in the products from the isomerization of 3-carene oxide, i.e., 3-carene, 3(10),4-caradiene, 3,3,6-trimethylcycloheptanone, and 3-caren-10-ol.
- Manukov, E. N.,Bazhina, G. N.
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p. 106 - 110
(2007/10/02)
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- Synthesis and Reactions of 4α-Acetoxycar-2-ene
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Epoxidation of 4α-acetoxycar-2-ene (III) with perbenzoic acid gives in addition to the epoxide IV, the rearranged hydroxy acetate (V).Under acidic conditions in different solvents, the epoxide IV rearranges to p-menthane derivatives V, VII and VIII.Rearrangement of IV under basic conditions gives rise to the p-menthane derivative IX which on oxidation with Jones chromic acid reagent gives as one of the products, a conjugated keto-γ-lactone, identified as X by spectral data.
- Naik, R. H.,Joshi, G. D.,Kulkarni, G. H.
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p. 306 - 307
(2007/10/02)
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- STEREOCHEMISTRY OF THE CARANE SYSTEM. OXIDATION PRODUCTS OF ISOMERIC 3,4-CARANEDIOLS OBTAINED FROM (+)-3-CARENE
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Oxidation of four isomeric 3,4-caranediols has been carried out and reaction products have been investigated.It has been found that cis-diols rather form cyclic ketals than are oxidized under conditions of the Jones reaction.The key intermediate for syntheses of chrysanthemic acid, (-)-2-acetonyl-3,3-dimethylcyclopropaneacetic acid was obtained exclusively by oxidation of (-)-3β,4α-caranediol.
- Hendrich, Aleksandra,Piatkowski, Krzysztof
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