EFFICIENT DIASTEREOSELECTIVE SYNTHESIS OF ERYTHRO-ALPHA-ALKYL-BETA-HYDROXY OR THREO-ALPHA-ALKYL-BETA-HYDROXY SULFONES BY REDUCTIONS OF ALPHA-ALKYL-BETA-KETO SULFONES WITH TICL4 BH3 OR LIE3BH/CECL3, RESPECTIVELY/

A stereoselective synthesis of erythro- and threo-alpha-alkyl-beta-hyd roxy sulfones by reduction of the corresponding alpha-alkyl-beta-keto sulfones has I,een developed. The pivotal role in this methodology is played by the chelating or nonchelating properties of the Lewis acid e mployed. The strong chelating TiCl4 led to the erythro isomer in high diastereomeric excess in noncoordinating solvents (CH2Cl2) at -78 degr ees C using BH3/py as reducing agent, while the nonchelating CeCl3 gav e a high excess of the three isomer in coordinating solvents (THF) at the same temperature using lithium triethylborohydride (LiEt3BH) as re ducing agent. Moreover, this methodology has been successfully utilize d for the synthesis of alpha-allyl-beta-hydroxy sulfones, which are us eful synthetic intermediates to obtain 2,5-disubstituted tetrahydrofur ans by electrophilic cyclization.