- Highly diastereoselective synthesis of β-hydroxy amides from β-keto amides
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β-Hydroxy amides with stereodefined geometry represent an important unit present in various natural products. The diastereoselective preparation of amides carrying a secondary or tertiary alcohol in β-position is described here.
- Bartoli, Giuseppe,Bosco, Marcella,Marcantoni, Enrico,Massaccesi, Massimo,Rinaldi, Samuele,Sambri, Letizia
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p. 3092 - 3096
(2007/10/03)
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- Crossed aldol reaction using cross-linked polymer-bound lithium dialkylamide
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Cross-linked polymer-bound lithium dialkylamides were employed in crossed aldol reaction of various carbonyl compounds with aldehydes to afford the corresponding β-hydroxycarbonyl compounds. The introduction of spacer chains to the polymer-bound lithium d
- Seki, Atsushi,Ishiwata, Fusae,Takizawa, Youichi,Asami, Masatoshi
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p. 5001 - 5011
(2007/10/03)
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- One-pot highly stereoselective reduction of β-keto amides to syn-γ-aminols
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In the presence of titanium tetrachloride, the borane/tetrahydrofuran complex can reduce 2-methyl-3-oxoamides into the corresponding syn-aminols in good yields and high diastereoselectivity. The use of borane/dimethyl sulfide instead of BH3/THF
- Bartoli, Giuseppe,Bosco, Marcella,Dalpozzo, Renato,Marcantoni, Enrico,Massaccesi, Massimo,Rinaldi, Samuele,Sambri, Letizia
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p. 8811 - 8815
(2007/10/03)
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- A mild aldol reaction of aryl aldehydes through palladium-catalyzed hydrosilation of α,β-unsaturated carbonyl compounds with trichlorosilane
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A mild aldol reaction of aryl aldehydestook place by using N,N- dimethylacrylamide and trichlorosilane with a catalytic amount of tetrakis(triphenyl-phosphine)palladium. A unique anti selectivity was observed in the reaction.
- Kiyooka, Syun-Ichi,Shimizu, Atsushi,Torii, Seiko
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p. 5237 - 5238
(2007/10/03)
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- Enolboration. 7. Dicyclohexyliodoborane, a Highly Stereoselective Reagent for the Enolboration of Tertiary Amides. Effects of Solvent and Aldolization Temperature on Stereochemistry in Achieving the Stereoselective Synthesis of either Syn or Anti Aldols
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A highly stereoselective enolboration of tertiary amides has been accomplished for the first time with dicyclohexyliodoborane, Chx2BI.A systematic study of the enolboration of representative N,N-dialkylpropionamides (CH3CH2CONR'2) with Chx2BI in the presence of various tertiary amines of variable steric requirements revealed an unusual aldol stereoselectivity in different solvents and at different aldolization temperatures.Both the nature of solvent and the aldolization temperature influence the stereochemistry of enolboration, with the solvent effect being greater than that of the temperature.Aliphatic and alicyclic hydrocarbon solvents favor formation of the syn aldols from the enol borinates by aldolization at lower temperature (-78 deg C), whereas most of the other solvents examined, such as aromatic and chlorinated aliphatic solvents, favor formation of the anti aldols by aldolization at relatively higher temperatures (0 or 25 deg C).The remarkable effects of both temperature and solvent in the case of tertiary amides raise a question about the validity of the previously assumed constancy of the Z to syn and E to anti relationship, suggesting either a possible isomerization of enol borinates with temperature or a different aldolization transition state with different solvent.While the effect of stric requirements of the dialkylamino group of the tertiary amide does not contribute significantly to the stereochemistry, that of the amine exerts a considerable influence.The present study establishes a simple procedure for the stereoselective synthesis of either syn or anti aldols from representative tertiary amides merely by changing the solvent and the aldolization temperature.
- Ganesan, Kumaraperumal,Brown, Herbert C.
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p. 7346 - 7352
(2007/10/02)
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- Chemistry of enoxysilacyclobutanes: Highly selective uncatalyzed aldol additions
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O-(Silacyclobutyl) ketene acetals derived from esters, thiol esters, and amides underwent facile aldol addition with a variety of aldehydes at room temperature without the need for catalysts. The uncatalyzed aldol addition reaction of O-(silacyclobutyl) ketene acetals displayed the following characteristics: (1) the rate of reaction was highly dependent on the spectator substituent on silicon and the geometry of the ketene acetal, (2) the O,O-ketene acetal of E configuration afforded the syn aldol products with high diastereoselectivity (93/7 to 99/1), (3) conjugated aldehydes reacted more rapidly than aliphatic aldehydes, and (4) the reaction was mildly sensitive to solvent. In addition, the aldol reaction was found to be efficiently catalyzed by metal alkoxides. Labeling experiments revealed that the thermal aldol reaction proceeds by direct intramolecular silicon group transfer, while the alkoxide-catalyzed version probably proceeds via in situ generated metal enolates. Computational modeling of the transition states suggests that the boat transition structures are preferred, supporting the observed syn selectivity of the thermal aldol reaction. Both thermal and alkoxide-catalyzed Michael additions were investigated, revealing a competition between 1,2- and 1,4-addition favoring the former.
- Denmark, Scott E.,Griedel, Brian D.,Coe, Diane M.,Schnute, Mark E.
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p. 7026 - 7043
(2007/10/02)
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- Stereoselective Addition of Organoaluminium or Organomanganese Reagents to α-Formyl Amides or α-Methyl-Substituted β-Keto Amides
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Treatment of α-formyl amides with RAlCl2 or PhAlCl2 provided threo-α-alkyl-substituted β-hydroxy amides under high stereocontrol.The method was successfully applied to the selective addition of alkyl group to α-methyl-substituted β-keto amides or esters.Treatment of α-methyl-β-keto amides or α-methyl-β-keto esters with trialkylaluminium or alkylmanganese halide afforded the corresponding erythro (or threo) α-methyl-substituted β-hydroxy amides or α-methyl-substituted β-hydroxy esters with high stereoselectivity.
- Taniguchi, Masahiko,Fujii, Hideaki,Oshima, Koichiro,Utimoto, Kiitiro
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p. 2514 - 2521
(2007/10/02)
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- Cerium(III) amide enolate. Addition to aldehydes and ketones
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The cerium(III) amide enolates, prepared in situ from the corresponding lithium enolates and anhydrous CeCl3, were found to undergo facile additions to ketones and aldehydes. Yields of the adducts are superior to those obtained using the lithiu
- Shang,Liu
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p. 2485 - 2489
(2007/10/02)
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- Stereoselective reduction of 2-methyl-3-oxo esters (or amides) with sodium borohydride catalyzed by manganese (II) chloride or tetrabutylammonium borohydride. A practical preparation of erythro and threo-3-hydroxy-2-methyl esters (or amides)
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erythro-3-Hydroxy-2-methylpropionates or erythro-3-hydroxy-2-methylpropionamides were prepared with high stereoselectivity by NaBH4 reduction of the corresponding 2-methyl-3-oxo esters or 2-methyl-3-oxo amides in the presence of a catalytic amount of manganese(II) chloride. On the other hand, reduction of these substrates with n-Bu4NBH4 provided threo-isomers selectively. erythro-Selective reduction of 2-methyl-3-oxo amides with NaBH3CN in 1N HCl-MeOH is also described.
- Taniguchi, Masahiko,Fujii, Hideaki,Oshima, Koichiro,Utimoto, Kiitiro
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p. 11169 - 11182
(2007/10/02)
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- Stereoselective addition of alkyl- or phenylaluminium dichloride to α-alkyl-β-formyl amides providing threo α-alkyl-β-hydroxy amides
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Treatment of α-alkyl-β-formyl amides with RAlCl2 or PhAlCl2 provided threo-α-alkyl-β-hydroxy amides under high stereocontrol.
- Fujii,Taniguchi,Oshima,Utimoto
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p. 4579 - 4580
(2007/10/02)
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- STEREOSELECTIVE ALDOL REACTIONS OF β-BORONATE CARBONYL DERIVATIVES.
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Deprotonation of β-boronate carbonyl derivatives can be readily achieved using LDA.Reaction of the resulting enolates with aldehydes gives the corresponding Aldol products, with high syn-selectivity for Z-enolates.This result is consistent with chelation enhanced stabilisation of the enolate geometry via the boronate moiety.
- Curtis, Anthony D. M.,Whiting, Andrew
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p. 1507 - 1510
(2007/10/02)
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- A PRACTICAL AND STEREOSELECTIVE REDUCTION OF 3-KETO-2-METHYL ESTERS OR 3-KETO-2-METHYL AMIDES INTO ERYTHRO-3-HYDROXY-2-METHYL ESTERS OR ERYTHRO-3-HYDROXY-2-METHYL AMIDES WITH NaBH4 CATALYZED BY MnCl2
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Erythro-3-hydroxy-2-methylpropionates or erythro-3-hydroxy-2-methylpropionamides were prepared with high stereoselectivity by NaBH4 reduction of the corresponding 3-keto esters or 3-keto amides in the presence of a catalytic amount of MnCl2.
- Fujii, Hideaki,Oshima, Koichiro,Utimoto, Kiitiro
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p. 6147 - 6150
(2007/10/02)
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- Cobalt(II) Catalyzed Coupling Reaction of α,β-Unsaturated Compounds with Aldehydes by the Use of Phenylsilane. New Method for Preparation of β-Hydroxy Nitriles, Amides, and Esters
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A new crossed coupling reaction of α,β-unsaturated nitriles with aldehydes was performed by using phenylsilane and a catalytic amount of bis(1,3-diketonato)cobalt(II) to give β-siloxy nitriles in good yields.Similarly, α,β-unsaturated amides and esters also reacted under the same conditions to afford β-siloxy amides or esters.The present reaction provides a new and facile method for preparation of β-hydroxy nitriles, amides, and esters.
- Isayama, Shigeru,Mukaiyama, Teruaki
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p. 2005 - 2008
(2007/10/02)
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- SUR LES ORGANOMETALLIQUES ISSUS DE THIOAMIDES. I. REACTIVITE AVEC LES ALDEHYDES ET CETONES; STEREOCHIMIE DE LA CONDENSATION AVEC LA t-BUTYL-4 CYCLOHEXANONE ET LE BENZALDEHYDE
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Organometallic compounds derived from thioamides RCH2CSN(R3)2 condense normally with aldehydes and saturated ketones.Condensation with 4-t-butylcyclohexanone leads predominantly to equatorial attack by the organometallic compound.These results suggest that the organometallic structure is RCH=C(SM)N(R3)2.The stereoselectivity of the reaction with benzaldehyde depends on R and R3; a mechanism for the formation of β-hydroxythioamides is discussed.
- Goasdoue, Claude,Goasdoue, Nicole,Gaudemar, Marcel,Mladenova, Margarita
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p. 279 - 292
(2007/10/02)
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