1,3-Dioxanone Derivatives from ?-Hydroxy-carboxylic Acids and Pivalaldehyde. Versatile Building Blocks for Syntheses of Enantiomerically Pure Compounds. A Chiral Acetoacetic Acid Derivative Preliminary Communication
作者:Dieter Seebach、J�rg Zimmermann
DOI:10.1002/hlca.19860690523
日期:1986.7.30
(R)-3-Hydroxybutyric acid (from the biopolymer PHB) and pivalaldehyde give the crystalline cis - or (R,R)-2-(tert-butyl)-6-methyl-1,3-dioxan-4-one (1a), the enolate of which is stable at low temperature in THF solution and can be alkylated diastereoselectively (3, 4, 5, and 7). Phenylselenation and subsequent elimination give an enantiomerically pure enol acetal 10 of aceto-acetic acid. Some reactions of
?-Alkylierung von ?-Hydroxycarbons�uren �ber 1,3-Dioxan-4-on-Enolate
作者:J�rg Zimmermann、Dieter Seebach、Tae-Kyu Ha
DOI:10.1002/hlca.19880710527
日期:1988.8.10
Highly Diastereoselective α‐Alkylation of β‐Hydroxycarboxylic Acids Through Lithium Enolates of 1,3‐Dioxan‐4‐onesFrom serine, β‐hydroxyisobutyric acid (‘Roche’ acid) and β‐hydroxybutyric acid, the dioxanones 1–6 were prepared. The generation of the enolates of type I with LDA at −75° and alkylation gave products with trans‐configuration whereas protonation of the 5‐methyl‐substituted enolate allowed access to the cis‐configurated β‐hydroxybutyric‐acid derivative 12. Hydrolysis gave the free β‐hydroxy acids of ‘syn’‐and ‘anti’‐configuration. Alkylation of the 6‐unsubstituted dioxanones 1 and 3 yielded predominantly products resulting from attack in the cis‐position of the t‐Bu group. The ‘reactive’ conformation of the enolates involved is tentatively derived from the product configuration. The selectivity of the alkylation is also discussed in terms of the results of an ab‐initio calculation on the enolates M–P.