Dissimilar reactivities of diastereomeric 1,1,1-trifluoro-3-(4-methoxyphenyl)-2,3-diphenylpropan-2-ols in an attempted elimination reaction

Attempted dehydration of a diastereomeric mixture of 1,1,1-trifluoro-3-(4-methoxyphenyl)-2,3-diphenyl-propan-2-ols (6a) with thionyl chloride in the presence of pyridine afforded the rearranged derivative 8 as the main product and only small amounts of the expected olefins (4, 5). Similar treatment of (2RS,3RS)-6a gave the rearrangement product 8 exclusively, while transformation of (2RS,3SR)-6a resulted in the formation of compounds 4, 5 and 8. The different reactivity of the diastereomers is rationalised.