Intramolecular 5-exo and 6-endo Cyclization of Polyepoxides

Tandem 5-exo-oxacyclizations of polyepoxides to form polycyclic ethers are well known. In Evans s synthesis of lonomycin A, diepoxide 66 underwent the desired 

The structure of glabrescol was subsequently revised, and the new structure was synthesized enantioselectively through sequential hydroxy-directed anti-oxidative cyclization of acyclic y-alkenols with VO(acac)2/TBHP to construct the adjacent THF rings via epoxides under acid conditions [35b], 

As an alternative to polyepoxide cyclization, cascade cyclization of cyclic sulfates 

Lindo-rv.ff oselecli ve oxacydization of polyepoxides is less common the first ster-eospedfic tandem endo-regioselective biomimetic oxacydization of polyepoxides to fused THP rings has only recently been reported [38a], The cyclization of the hydroxy-methoxymethyl-substituted triepoxide 75 (a 1,4,7-triepoxide), promoted and directed by La(OTf)3 through an intramolecular chelation and based on a procedure originally described for a monoepoxide system [38b], afforded the tri- 

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