Cytotoxic compounds. Part IX. The dimethanesulphonates of 3-phenylthiopropane-1,2-diol and of 2-phenylthiopropane-1,3-diol; their reactions with nucleophiles, and rearrangements through sulphonium ions

Abstract

The products formed in the reactions of each of the above dimethanesulphonates with various nucleophiles have been examined by nuclear magnetic resonance spectroscopy. Substitution without rearrangement is the main reaction with methanolic sodium phenyl sulphide, sodium benzyl sulphide, and sodium ethyl sulphide, whilst elimination is dominant with tetraethylammonium acetate in acetone and with methanolic sodium methoxide. During solvolysis in acetic acid, thermodynamic control is established, and both dimethanesulphonates give only 3-phenylthiopropane-1,2-diol diacetate, but with potassium acetate in acetic anhydride each forms a mixture of the 1,2- and the 1,3-diacetate. Solvolysis in methanol also gives a mixture, of the 1,2- and the 1,3- dimethyl ether. The compositions of these mixtures, formed under kinetic control, considered in conjunction with the probable sequence of reactions involved, indicate that the primary carbon atom in the intermediate unsymmetrical cyclic sulphonium ions is preferentially, but not exclusively, attacked.

Unusual features were present in the nuclear magnetic resonance spectra of 1,2,3-trisphenylthiopropane (sharp singlet for the five non-aromatic protons) and 1,2-bisbenzylthio-3-phenylthiopropane (sharp singlet for the fifteen aromatic protons).