- Diastereoselectivity in heterogeneous catalytic hydrogenation of Baylis-Hillman adducts. Total synthesis of (±)-sitophilate
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We describe herein a highly diastereoselective total synthesis of racemic sitophilate, based on the results obtained in a diastereoselective heterogeneous catalytic hydrogenation reaction of a set of Baylis-Hillman adducts originating from aliphatic aldehydes.
- Mateus, Cristiano R,Feltrin, Melissa P,Costa, Ana M,Coelho, Fernando,Almeida, Wanda P
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- New synthesis of (±)-sitophilate using carboxylic acid dianion methodology - A stereoselectivity study
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A simple two-step synthesis of (±)-sitophilate in has been developed by addition of propanal to the lithium enediolate of propanoic acid and subsequent esterification with 3-pentanol under standard Fischer conditions. Efforts to control the diastereoselectiv-ity to generate the syn isomer are described. A modest degree of asymmetric induction is found using chiral amides as base. Georg Thieme Verlag Stuttgart.
- Gil, Salvador,Parra, Margarita,Rodriguez, Pablo,Sotoca, Enrique
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p. 3451 - 3455
(2007/10/03)
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- Asymmetric aldol reactions. A new camphor-derived chiral auxiliary giving highly stereoselective aldol reactions of both lithium and titanium(IV) enolates
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A new, conformationally rigid camphor-derived N-propionyloxazolidinone effects asymmetric stereochemical control in syn-selective aldol condensations of the derived lithium and titanium(IV) enolates with a variety of aldehydes. Simple and diastereofacial selectivities of the reaction are high, and diastereomeric purities of the crude aldol adducts can be improved, usually by a single recrystallization, to levels of 98-99% in most cases. The observed facial selectivity is best explained by a transition structure in which intramolecular chelation between the oxazolidinone carbonyl oxygen and the metal induces an enolate π-facial differentiation; the major products observed are those expected from chelation control. Hydrolysis of the exocyclic carbonyl of the aldol adducts led to β-hydroxy-α-methylcarboxylic acids, with recovery of the chiral auxiliary. Consonant double-asymmetric induction with (R)-2-(benzyloxy)propanal gave the product expected from oxazolidinone chelation but nonchelation of the aldehyde benzyloxy group.
- Bonner, Mary Pat,Thornton, Edward R.
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p. 1299 - 1308
(2007/10/02)
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- A VERSATILE SYNTHESIS OF 3-SUBSTITUTED 5-ALKYL BUTYROLACTONES VIA DYOTROPIC REARRANGEMENT
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Substituted acetic acid dianions are convertable to 3,5-disubstituted butyrolactones, employing a dyotropic rearrangement as the key step.
- Black, T. Howard,Fields, John D.
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p. 125 - 130
(2007/10/02)
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- CHIRAL PROPIONATE ENOLATE EQUIVALENTS FOR THE STEREOSELECTIVE SYNTHESIS OF THREO- OR ERYTHRO-α-METHYL-β-HYDROXY ACIDS.
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The aluminium and copper enolates derived from (n5-C5H5)Fe(CO)(PPh3)COCH2CH3 are chiral propionate enolate equivalents which on reaction with aldehydes (RCHO, R=Me, Et, iPr, tBu) provide stereoselective sytheses of threo-
- Davies, Stephen G.,Dordor-Hedgecock, Isabelle M.,Warner, Peter
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p. 2125 - 2128
(2007/10/02)
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- Chiral Acetate Enolate Equivalent for the Synthesis of β-Hydroxy Acids
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The aluminium enolate derived from (η5-C5H5)Fe(CO)(PPh3)(COMe) undergoes stereoselective aldol condensations with aldehydes to generate β-hydroxy acyl complexes which yield β-hydroxy acids on decomplexation.
- Davies, Stephen G.,Dordor, Isabelle M.,Warner, Peter
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p. 956 - 957
(2007/10/02)
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- ERYTHROSELECTIVITY IN ADDITION OF γ-SUBSTITUTED ALLYLSILANES TO ALDEHYDES IN THE PRESENCE OF TITANIUM CHLORIDE
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(E)-Crotyltrimethylsilane and (E)-cinnamyltrimethylsilane were allowed to react with aldehydes (RCHO: t-Bu, i-Pr, Et, Me) in the presence of titanium chloride to give erythro homoallyl alcohols with over 93percent selectivity.Lower erythroselectivity was observed in the reaction of (Z)-allylsilanes.
- Hayashi, Tamio,Kabeta, Keiji,Hamachi,Itaru,Kumada, Makoto
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p. 2865 - 2868
(2007/10/02)
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- ACYCLIC STEREOSELECTION-13; ARYL ESTERS: REAGENTS FOR THREO-ALDOLIZATION
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Preformed Li enolates of hindered aryl esters condense with aldehydes to give predominantly threo aldols.The method has been explored with esters 3 (DMP propionate), 4 (BHT propionate), 5 (DBHA propionate).DMP propionate reacts with benzaldehyde and α-unbranched aliphatic aldehydes to give threo:erythro ratios of about 6.5:1.However, with α-branched aliphatic aldehydes, ester 3 gives only threo-aldols.BHT propionate and DBHA propionate give only threo-aldols with all aldehydes studied.The DMP aldols may be converted into β-hydroxy acids by simple hydrolysis with KOH in aqueous methanol.BHT aldols cannot be hydrolyzed without retroaldolization.However, these aldols can be reduced to diastereomerically pure 1,3-diols.The DBHA aldols can converted into β-hydroxy acids by a method involving oxidation with ceric ammonium nitrate (CAN) in aqueous acetonitrile.Threo-selectivity is also seen in the condensations of DMP butyrate (15), DBHA butyrate (16), DMP pentenoate (17), and BHT pentenoate (18).The approach has been utilized in a stereoselective synthesis of racemic methyl corynomycolate.
- Heathcock, Clayton H.,Pirrung, Michael C.,Montgomery, Stephen H.,Lampe, John
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p. 4087 - 4095
(2007/10/02)
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