ISSN:
1434-193X
Keywords:
Fluoro analogs of vitamin A
;
Horner-Wittig reaction
;
Fluoroisoprenoid building blocks
;
Stereoselectivity
;
Hydrolysis of chlorofluorocyclopropanes
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
An improved method for the preparation of ethyl 2-fluoro-3-methyl-2-butenoate (3) is described. The two stereoisomers [(E)-4 and (Z)-4] obtained after γ-bromination can be separated and can be individually converted into the corresponding diethyl phosphonates. The PO-ylides generated by α-deprotonation of the latter lose their stereochemical integrity by rapid torsional equilibration of the ester tail. Thus, Horner-Wittig reactions accomplished with benzaldehyde and (Z)- or (E)-(β-ionylidene)-acetaldehyde lead inevitably to stereorandomization at the terminal, ethoxycarbonyl-bearing double bond affording (E)- and (Z)-isomers in 50:50 to 15:85 ratios, depending on the reaction conditions. The new double bond, however, is formed with perfect trans-selectivity.
Type of Medium:
Electronic Resource
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