A Catalytic, Enantioselective Formal Synthesis of (+)-Dichroanone and (+)-Taiwaniaquinone H

A catalytic, enantioselective
formal synthesis of (+)-dichroanone
and (+)-taiwaniaquinone H is reported. The all-carbon quaternary stereocenter
was constructed by asymmetric conjugate addition catalyzed by a palladium­(II)
(S)-tert-butyl­pyridino­oxazoline complex.
The unexpected formation of a [3.2.1] bicyclic intermediate required
the identification of a new route. Analysis of the Hammett constants
for para-substituted arenes enabled the rational
design of a highly enantioselective conjugate addition substrate that
led to the completion of the formal synthesis.