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.
Brown
J M
JM
Dyson Perrins Laboratory, Oxford, UK. bjm@ermine.ox.ac.uk
Leppard
S J
SJ
Oakes
J
J
Thornthwaite
D
D