Synthèses Asymétriques Potentielles Impliquant la Réaction “Ene”

Racemic “ene” syntheses have been carried out to evaluate the potentiality, in asymmetric syntheses, of the corresponding optically active inducers. The (dl)‐crotonates 5 to 8 were prepared from (dl)‐hydroxyheptahelicene 1 and the sec. alcohols 2, 3 and 4. Chemical yields are shown in table 1 (85–94%). These (dl)‐crotonates underwent the “ene” reaction with cyclohexene in the presence of SnCl4 to give the corresponding diastereomeric (dl)‐esters 9, 10, 11 and 12, with respectively ∼100, 48, 70 and ∼100% diastereomeric excesses. Copyright © 1987 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim