Mecanisme de la reaction de Horner-Emmons—II: Effet de solvant sur la stereoselectivite de la reaction d'aldehydes aromatiques et de phosphononitriles

The ratio of Z and E cinnamonitriles obtained from aromatic aldehydes and phosphonitriles 1a and 1b mainly depends upon solvent and upon the phosphonate nature. If it has two H α to CN (1b), the solvent affects the equilibrium of the intermediate oxyanions 5b and 6b. The aldolization step reversibility and stereoselectivity does not intervene unless the aldehyde is orthosubstituted. If the phosphonate has only one H α to CN, kinetically controlled stereoselectivity of the whole process depends upon the solvent effect upon reversibility factor and aldolization selectivity: in DME and THF the total stereoselectivity is low, while in HMPT, the E isomer predominates; under equilibrating conditions (HNa-HMPT) the Z isomer predominates.