Tetrahydropyran formation by rearrangement of an epoxy ester: a model for the biosynthesis of marine polyether toxins.

Acid-catalyzed rearrangement of the (S)-epoxide derived from 2alpha-allyl cholestanyl acetate resulted in a 1:1 mixture of a steroidal tetrahydrofuran and a steroidal tetrahydropyran. Formation of a six-membered ring supports the hypothesis that epoxy ester-orthester-cyclic ether rearrangement may be involved in the biosynthesis of ladder-type marine polyether toxins. This reaction represents a new biomimetic preparation of medium ring cyclic ethers.