Dimethylprolinol Versus Diphenylprolinol in CuBr2-Catalyzed Enantioselective Allenylation of Terminal Alkynols

Abstract The CuBr 2 -catalyzed enantioselective allenylation of terminal alkynols with carbon chains of different lengths has been developed. Compared with ( S )-α,α-diphenylprolinol, the reaction using ( S )-α,α-dimethylprolinol as the chiral amine afforded optically active 1,3-disubstuted allenols with higher ee -values. Both aliphatic and aromatic aldehydes could be applied. The naturally occurring phlomic acid was synthesized in four steps from commercially available hex-5-yn-1-ol.