ISSN:
0009-2940
Keywords:
(R)-3-Hydroxybutyric acid
;
Cuprate Michael addition
;
Li enolates of 1,3-dioxan-4-ones
;
Li enolate protonation, steric course of
;
EPC synthesis
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
(E,R,R)-5-Alkylidene-2-tert-butyl-6-methyl-1,3-dioxan-4-ones: Preparation from (R)-3-Hydroxybutyric Acid, Cuprate Additions, and Hydrolyses to 3-Hydroxycarboxylic Acids with Chiral Secondary Alkyl Substituents in the 2-PositionLi enolates of (R,R)-2-tert-Butyl-6-methyl-1,3-dioxan-4-one add to aliphatic or aromatic aldehydes with relative topicity Re,Re (2: 1 to 10: 1, 9 examples). The title compounds are obtained from these aldol adducts by dehydration through mesylates (5 examples, total yields from the dioxanone 35-55%). Cuprate additions (R2CuLi/F3B—OEt2) to these alkylidene dioxanones and quenching with acid produce 5,6-trans-substituted dioxanones in an overall anti addition of R and H to the exocyclic double bond from the Re and the Si face, respectively (5: 1 to 40:1, 13 examples, 50-80%). The configurations of the products were assigned by NMR spectroscopy and by chemical correlation. In 8 cases, the dioxanone products were hydrolysed to the corresponding free β-hydroxycarboxylic acids. It is also demonstrated that transacetalisation of the aldol adducts leads to 1,3-dioxane-5-carboxylic acids (acetal-protected derivatives of “double aldols”, formally derived from acetic acid, 4 examples). Reduction of these acids with LAH, in turn, produces tris(hydroxyalkyl)methanes (acetal-protected, 3 examples). All chiral products described herein are enantiomerically pure.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19901231225
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