Synthesis of trans‐syn‐trans Fused Bis‐Pyrans via endo‐Selective Cyclizations of Cyclic Sulfates.

Abstract Acid-catalyzed cyclization of hydroxy-cyclic sulfates occurs with endo -regioselectivity affording bispyran products from substrates in which the nucleophilic hydroxyl and electrophilic cyclic sulfate groups are 1,2- trans -substituted on a cyclic pyran template. This methodology is demonstrated in an enantioselective synthesis of the trans-syn-trans fused AB cyclic ether rings of the brevetoxin natural products.