The chiral alcohol was carried directly into the
cyclization step to form the chiral cyclic ether 34.
Instead of oxidizing at this point, which would have
also pointlessly destroyed the hard won chirality, a
new route was developed to permit an alternative to
the oxonium salt route. The oxidation required at the
benyzlic center was accomplished by air via a base
mediated oxidation using sodium hydroxide in
DMSO to establish the hemiketal 35 (Scheme 9).