The total synthesis of Hemibrevetoxin B is described. A new cyclization approach, based on the Lewis acid mediated intramolecular cyclization of the gamma-oxo-substituted allylic tin having an aldehyde group, produced the 6-6-7-7 polycyclic ether skeleton of the natural product with high stereoselectivity. The H-1 and C-13-NMR spectra of synthetic hemibrevetoxin B was identical with those of natural product.