Generation of Nucleophilic Chromium Acetylides from gem‐Trichloroalkanes and Chromium Chloride: Synthesis of Propargyl Alcohols

Abstract

Nucleophilic mixed chromium(II) and chromium(III) acetylides are generated from the smooth reduction of primary 1,1,1-trichloroalkanes with chromium(II) chloride in the presence of an excess amount of triethylamine at room temperature. These species arise from chromium(III) vinylidene carbenoids. It has been demonstrated that uncommon low-valent CrII acetylides are formed by C–H insertion of CrIICl2 into terminal alkynes, formed in situ through the Fritsch– Buttenberg–Wiechell (FBW) rearrangement, whereas CrIII acetylides are concomitantly generated by HCl elimination from the chromium(III) vinylidene carbenoid. Both divergent pathways result, overall, in the formation of nucleophilic acetylides. In situ trapping with electrophilic aldehydes afforded propargyl alcohols. Furthermore, deuteration experiments and the use of deuterium labeled 1,1,1-trichloroalkane substrates demonstrated the prevalence of low-valent CrII acetylides, potentially useful, yet highly elusive synthetic intermediates.