Chiral organometallic reagents, part 26 Highly enantiomerically enriched alpha-haloalkyl Grignard reagents

alpha-Chloro- and alpha-bromoalkyl Grignard reagents 11 and 30 with >97% ee (enantiomeric excess) were generated by a sulfoxide/magnesium exchange rea ction from the enantiomerically and diastereomerically pure sulfoxides 25 a nd 27 The resulting alpha-haloalkyl Grignard reagents are configurationally stable at -78 degrees C. Racemization sets in at or above -60 degrees C, e specially when the solution contains bromide ions. In the absence of halide ions, the configurational stability extends up to -20 degrees C, when chem ical decomposition commences.