Structural studies on 6-ethoxytetrahydropyrylium cations; stereoelectronic control in the reactions of lactonium salts

The structures of 6-ethoxy-2,3,4,5-tetrahydropyrylium, 1, 6-ethoxy-2-methyl-2,3,4,5-tetrahydropyrylium, 2, and 2-ethoxy-3,4,4a,5,6,7,8,8a-octahydro-1-benzopyrylium, 3, hexachloroantimonates have been determined by X-ray crystallography. In each case the tetrahydropyrylium rings exist in shallow half-chair conformations with the cationic centers C(6), C(5), O(1), and O(6) having a planar arrangement. The cations all have a Z conformation about …