Stereocontrolled synthesis of the 6-7-7-6 ring system of polycyclic ethers via the intramolecular reaction with ω-tributylstannyl ether aldehydes

: The BF3.OEt2 mediated cyclization of ω-tributylstannyl ether aldehyde 1 produces seven-membered cyclic ethers 2 in 95% yield with high diastereoselectivity (2a:2b = 93:7). Perfect stereocontrol between a and α’ proton is accomplished in the cyclization to give the cis products, and the stereochemistry between a and p proton is controlled to trans resulting in the predominant formation of the anti isomer 2a. This allylic tin method is applied to the stereocontrolled synthesis of 6,7,7,6-polycyclic ether skeleton as a model synthesis of brevetoxin B.