Influence of the Azulene Ring on the Enantioseparation of 1,5-Diols

Abstract

The enantioseparation of a series of six azulene-centered 1,5-diol enantiomers was studied employing two cellulose-based chiral stationary phases under normal phase conditions (isopropanol/hexanes). The separations were generally quite good on Chiralcel-OD-H, with α values ranging from 1.2 to 8.4 (average 4.0) and resolution values of 0.4-8.3 (average 4.7). Only one of the six enantiomer pairs was not well resolved, but was well separated on Lux cellulose 2 (α 1.4, R s 8.7). It was observed that the enantioseparations of the RS/SR diastereomers (ave α = 7.8, R s = 8.2) were dramatically better than that of the corresponding RR/SS diastereomers (ave α = 2.1, R s = 3.0) on Chiralcel-OD-H. The better-resolved diastereomer pairs correspond to the more strongly retained diastereomers on silica gel. The enantiomers of two benzene 1,5-diols were much more poorly separated on both stationary phases, suggesting that the unusual polarity of the azulene ring enhances critical interactions with these phases.