Synthesis of enantiopure aliphatic acetylene alcohols and determination of their absolute configurations by ¹H NMR anisotropy and/or X-ray crystallography

The MαNP acid method has been applied to racemic aliphatic acetylene alcohols in order to simultaneously prepare enantiopure alcohols and to determine their absolute configurations by ¹H NMR anisotropy. Racemic acetylene alcohols 6-8, 11, and 20 were esterified with MαNP acid (S)-(+)-1 to yield diastereomericMαNP esters which were efficiently separated by HPLC on silica gel with separation factors α in the range 1.60-1.93. The ¹H NMR anisotropy factors Δδ [= δ(2nd fr.) - δ(1st fr.)] were calculated from the data of the first- (22a-27a) and second-eluted MαNP esters (22b-27b). The absolute configurations of the first-eluted esters were determined from the distribution of Δδ values in the MαNP sector rule. In the case of MαNP ester 26b, the assigned absolute configuration was confirmed by X-ray crystallography. The solvolysis of MαNP esters yielded enantiopure acetylene alcohols 5-8 with established absolute configurations.