Stereoselective Synthesis, Structural Studies, and Hydrolysis of Tricyclic Alkoxysulfonium Salts

The crystal and molecular structure of endo tertiary alcohol lb determined by X-ray crystallographic techniques is reported. The molecule crystallizes in the space group P2₁/n with α = 14.628 (7) Å, b = 5.648 (1) Å, c = 14.973 (8) Å, β = 113.78 (4)°, Z = 4. This structure features an unsymmetrical contra twist of the norbornyl skeleton and an intramolecular hydrogen bond between the sulfur atom and hydroxyl group with a very short distance of 3.119 Å. IR spectroscopic studies provide evidence for this intramolecular hydrogen bond in dilute solutions of endo tertiary alcohol 1b but not in endo primary alcohol 1a. Treatment of endo primary alcohol 1a and endo tertiary alcohol 1b with tert-butyl hypochlorite followed by mercury(II) chloride provides the corresponding alkoxysulfonium salts 2a and 2b, respectively. The crystal and molecular structures of these salts were determined by single-crystal X-ray studies. These salts crystallize in the space groups P2₁/c and P1, respectively, with α = 10.152 (3) Å, b = 11.857 (4) Å, c = 12.087 (3) Å, β = 97.98 (2)°, Z = 4, and α = 8.416 (3) Å, b = 9.678 (3) Å, c = 10.688 (4) Å, β = 87.72 (3)°, Z = 2, respectively. Both structures feature short S–O bond lengths of 1.58 (1) Å and 1.587 (4) Å, respectively, and large S–O–C (8) bond angles of 121.2 (9)° and 124.0 (3)°, respectively. Base hydrolysis of these salts produces the corresponding sulfoxides 11a and 11b by nucleophilic attack by hydroxide ion on sulfur.