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A synthesis of the C29-C51 fragment of spongistatin 1, containing the E and
F rings, has been completed. The approach relies on four diastereoselectiv
e aldol additions and an asymmetric glycolate alkylation to establish eight
of the eleven stereogenic centers. The intact chlorodiene side chain was a
ppended by a Lewis acid catalyzed addition of an allylstannane to an epoxy
enol ether.