Key steps in a synthesis of the C17-C32 fragment of
ionomycin are (a) an auxiliary-directed oxidative cyclisation
of a diene with potassium permanganate to construct a tetrahydrofuran
ring and four stereogenic centres in a single operation, and (b)
a chain-appendage reaction featuring the alkylation of an enolsilane
by an oxocarbenium ion generated from a 2-phenylsulfonyl-substituted tetrahydrofuran.
ionomycin - permanganate oxidation - directed
reduction - crotylboration - carbocupration