OXIDATIVE CYCLIZATION OF 3-(AMINO)THIOETHERS TO FORM S-SUBSTITUTED ISOTHIAZOLIDINIUM SALTS

The reaction in which methionine is cyclized to form dehydromethionine (S-methylisothiazolidinium-3-carboxylate) by iodinic oxidation at neutral pH3 has now been shown to be a general one for compounds possessing an amine group γ to a thioether function. Thus, the reaction provides a convenient route to the preparation of N-protonated, cyclic sulfilimines. The S-substituted isothiazolidinium salts from ethionine, S-phenylhomocysteine, S-benzylhomocysteine, and 3-(methylthio)propylamine were prepared and characterized by elemental analyses and NMR spectra. Cyclization of L-methionine was shown to produce a mixture of diastereomers which are chiral at positions 1 (sulfur) and 3. Evidence was obtained that hydrolysis of each diastereomer to form the sulfoxide proceeds with inversion of configuration. Oxidative cyclization of 3-(amino)thioethers was found to also be induced by a variety of N-halo derivatives and by lead tetraacetate. © 1979, American Chemical Society. All rights reserved.