A convenient strategy that is ideally suited for the
construction of all the naturally occurring
cyclohexane diepoxides and cyclohexene epoxides is described. The
key intermediate 12, a 1,3-cyclohexadiene, has been prepared from (−)-quinic acid in 11 steps
with 18% overall yield. Singlet
oxygen photooxygenation of the 1,3-cyclohexadiene followed by
rearrangement of the resultant
endoperoxides with either cobalt-meso-tetraphenylporphyrin
or trimethyl phosphite afforded
enantiopure (+)-crotepoxide, (+)-boesenoxide, and
(−)-iso-crotepoxide or (−)-senepoxide,
(+)-β-senepoxide, (+)-pipoxide acetate, and (−)-tingtanoxide,
respectively.