Fluorinated analogs of retinoids. Stereocontrolled synthesis employing fluoroisoprenoidal Horner ylides

An improved method for the prepn. of Me2C:CFCO2Et is described. The two stereoisomers (E)- and (Z)-BrCH2CMe:CFCO2Et obtained by g-bromination are sepd. and can be individually converted into the corresponding phosphonates. The PO-ylides generated by a-deprotonation of the latter lose their stereochem. integrity by rapid torsional equilibration of the ester tail. Thus, Horner-Wittig reactions accomplished with PhCHO and (Z)- or (E)-(b-ionylidene)acetaldehyde lead inevitably to stereo-randomization at the terminal, CO2Et-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. [on SciFinder (R)]


Published in:
European Journal of Organic Chemistry, 11, 2603-2607
Year:
1998
Keywords:
Note:
CAN 130:81662 30-40 Terpenes and Terpenoids Institut Chimie Organique, Batiment Chimie,Universite Lausanne,Lausanne,Switz. Journal 1434-193X written in English. 79-77-6 (b-Ionone); 97-62-1 (Ethyl isobutyrate); 100-52-7 (Benzaldehyde); 23521-49-5 ((Z)-1-Bromo-2-ethoxyethene) Role: RCT (Reactant), RACT (Reactant or reagent) (stereoselective prepn. of fluorinated retinoid analogs via fluoroisoprenoidal Horner ylides); 685-89-2P; 2609-24-7P; 2609-26-9P; 2945-32-6P; 3917-41-7P; 3917-45-1P; 3917-46-2P; 31469-16-6P; 54226-17-4P; 218916-06-4P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (stereoselective prepn. of fluorinated retinoid analogs via fluoroisoprenoidal Horner ylides); 218898-20-5P; 218898-21-6P; 218898-22-7P Role: SPN (Synthetic preparation), PREP (Preparation) (stereoselective prepn. of fluorinated retinoid analogs via fluoroisoprenoidal Horner ylides)
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