Synthesis of medium-sized cyclic allylic ethers by ring-closing metathesis and subsequent elaboration to sub-units found in the brevetoxins and ciguatoxins

Saturated and unsaturated seven- and eight-membered cyclic ethers of the type found in the brevetoxins and ciguatoxins have been prepared in enantiomerically pure form in 10 steps from a readily available chiral pool material. The key steps in this sequence are ring-closing metathesis of allylic ethers, and subsequent elaboration of the cyclic allylic ether products by stereoselective epoxide formation and ring-opening. (C) 1998 Elsevier Science Ltd. All rights reserved.