77302-11-5Relevant articles and documents
New synthesis of (±)-sitophilate using carboxylic acid dianion methodology - A stereoselectivity study
Gil, Salvador,Parra, Margarita,Rodriguez, Pablo,Sotoca, Enrique
, p. 3451 - 3455 (2007/10/03)
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.
Asymmetric aldol reactions using (S,S)-(+)-pseudoephedrine-based amides: Stereoselective synthesis of α-methyl-β-hydroxy acids, esters, ketones, and 1,3-syn and 1,3-anti diols
Vicario, Jose L.,Badia, Dolores,Dominguez, Esther,Rodriguez, Monica,Carrillo, Luisa
, p. 3754 - 3759 (2007/10/03)
A very efficient method for performing stereoselective aldol reactions is reported. The reaction of (S,S)-(+)-pseudoephedrine-derived propionamide enolates with several aldehydes yielded exclusively one of the four possible diastereomers in good yields, although transmetalation of the firstly generated lithium enolate with a zirconium(II) salt, prior to the addition of the aldehyde, is necessary in order to achieve high syn selectivity. The so-formed syn-α-methyl-β-hydroxy amides were transformed into other valuable chiral nonracemic synthons such as α-methyl-β-hydroxyacids, esters, and ketones. Finally, a stereocontrolled reduction procedure starting from the so-obtained α-methyl-β-hydroxy ketones has been developed allowing the synthesis of either 1,3-syn- or 1,3-anti-α-methyl-1,3-diols in almost enantiopure form by choosing the appropriate reaction conditions.
Asymmetric aldol reactions. A new camphor-derived chiral auxiliary giving highly stereoselective aldol reactions of both lithium and titanium(IV) enolates
Bonner, Mary Pat,Thornton, Edward R.
, p. 1299 - 1308 (2007/10/02)
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.
