Total Synthesis of Natural
Enantiomers of Heliespirones
A and C <i>via</i> the Diastereoselective Intramolecular
Hosomi-Sakurai Reaction
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Abstract
A full account of the development of a novel type of
the intramolecular
Hosomi-Sakurai reactions of the substrates with a <i>p</i>-benzoquinone and an allylsilane moieties connected by an ether linkage
is described. This transformation proceeds <i>via</i> an
addition–elimination sequence and provides the products with
two stereogenic centers through a 1,3(or 1,4)-asymmetric induction
in good to excellent diastereoselectivities. A reasonable mechanistic
possibility for the reaction, determination of the stereochemistry
for the product, and scope and limitation of the transformation are
also discussed. The methodology developed here can successfully be
applied to the enantiocontrolled total synthesis of the natural enantiomers
of (−)-heliespirone A and (+)-heliespirone C, which have been
isolated from sunflower <i>Helianthus annuus</i> L. as allelochemicals