SELECTION SIMPLE ET DIASTEREOFACIALE DE LA REACTION D' ALDOLISATION DE L' ACIDE PROPANEDITHIOIQUE

Article abstract of DOI:10.1016/S0040-4020(01)89080-3

Lithium enedithiolate, obtained by double deprotonation of propanedithioic acid with LDA, reacts at -50 deg C diastereoselectively with achiral aldehydes forming aldols with syn-anti ratios ranging from 1/5 to 9/1.The selectivity observed does not depend of time and temperature and, the aldolisation still occurs at 0 deg C with a better yield without alteration of the stereoselectivity.The selectivity variation induced by using other cation instead of lithium and the influence of a crown ether are fully explained by a classic chair like transition state.The same lithium enedithiolate reacts at -120 deg C stereoselectively with chiral aldehydes affording anti-syn aldols and syn-syn aldol in the particular case of 2-phenyl propanal.The yields are improved by increasing the reaction temperature up to 0 deg C with the same selectivity.The aldol configurations are stated by comparison of the HPLC retention time of aldol mixture with that of authentic syn or syn-syn major aldol mixture prepared by known diastereoselective aldol reactions of methyl propanedithioate.Confirmation of aldol configurations by 1H and 13C NMR spectra are given.