A Simple Strategy for Determining the Absolute Configurations of Acyclic 1,2,4,6,8-Pentols

A simple procedure for assigning the absolute stereochemistry of 1,3-polyols containing four chiral centers using the CD exciton chirality method is presented. Eight possible diastereoisomers of 10-undecene-1,2,4,6,8-pentols with established absolute configurations were used as models to develop the strategy. The C2 and C4 configurations are established from the sign and amplitude of the difference CD spectrum between the pentabenzoate and the 1-O-pivaloyl tetrabenzoate, respectively, thus reducing the possible configurations from 16 to 4. The stereochemistry of the C8 chiral center is directly assigned from the CD analysis of the 1-O-pivaloyl tetrabenzoate; tetrabenzoates having a 2,8-syn configuration exhibit weak CD curves whereas the 2,8-anti tetrabenzoates exhibit strong exciton split curves. This analysis further reduces the possible stereoisomers to two. The final configurational assignment at C6 is performed by the 13C NMR analysis of the diacetonide derived from the 1-O-pivaloyl 2,4,6,8-tetrols. Advantages of the present method are that the requisite transformations involve only four simple steps and that reference samples are not necessary.