Synthesis of mono and gem-dihalogeno-olefins from carbonyl compounds and in situ generated lithium carbenoids

Abstract

The treatment of carbonyl compounds (5) with dihalogenomethane and lithium dicyclohexylamide at –78 °C leads after acid hydrolysis to the crude alcohols (6), which by silylation with trimethylchlorosilane–hexamethyldisilazane–pyridine affords the crude silylated alcohols (7); final treatment of compound (7) with lithium di-isopropylamide or butyl-lithium (when one of the halogens is bromine) at low temperature gives the corresponding di- or mono-halogenated olefins (8) or (9), respectively, through a sole β-elimination process.