Diastereoselectivity in scalemic tartrate/titanium epoxidations.

Nonlinearity in the diastereoselectivity of epoxidation of allylic alcohols with mixtures of titanium isopropoxide, tertbutyl hydroperoxide, and diethyl tartrate was observed. Racemic and enantiomerically pure alcohols E-2-methyl-4-hexen-3-ol and E-1-methoxy-5-(O-tertbutyldimethylsilyloxy)-2-penten-4-ol were prepared. Epoxidation reactions were carried out with Ti(OPri)4 and ButOOH accompanied by diethyl tartrate of varying enantiomeric purity. The simplest explanation of these results is that a dimeric epoxidation reagent is involved, with significantly different reactivity for the homochiral and racemic forms.
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