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Benzyl p-tolyl sulfoxide (1) was found to racemize some 1000 times faster on heating than comparable diaryl, alkyl aryl, or dialkyl sulfoxides. The mechanism for racemization involves homolysis of the benzylic carbon-sulfur bond. Competition by a pyramidal inversion mechanism has been rigorously excluded. The radical pair formed in the first step of the bond cleavage is not involved in the thermal rearrangement of benzyl ptoluenesulfenate (2) to benzyl p-tolyl sulfoxide, a reaction which appears to proceed by an intramolecular, concerted mechanism.

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Treatment of (+)-(R)-methyl p-tolyl sulfoxide ((+)-(/?)-!) of maximum rotation with either N-sulfinyl-/7-toluenesulfonamide or N,N'-bisO-toluenesulfonyl)sulf ur diimide in pyridine at 0°g ave (80 and 95%) (-)-(S)-N-(p-tosyl)methyl-p-tolylsulfimide ((-)-(S)-II), which in base at 25°g ave (94%) (+)-(/?)-! of 94% optical purity. Imidation of (+)-(i?)-I of maximum rotation with tosyl azide gave (70%) ( -)-(7?)-A7-tosylmethyl-p-tolylsulfoximide ((-)-(i?)-III) of 99% maximum rotation. Oxidation of (-)-(S)-II of maximum rotation with mchloroperbenzoic acid gave (65%) (-)-(7?)-III of 98 % maximum rotation. Hydrolysis of (-)-(7?)-III of maximum rotation with concentrated sulfuric acid at 25°g ave (99%) (-)-(i?)-methyl-p-tolylsulfoximide ((-)-(i?)-IV) of 99% maximum rotation. Conversion of (-)-(/?)-!V of maximum rotation to (-)-(i?)-III was accomplished either with pyridine and tosyl chloride (86% yield, 99% maximum rotation) or by treatment of (-)-(/?)-IV with first sodium and benzene followed by tosyl chloride (62, 97% of maximum rotation). Sulfoximide, (-)-(7?)-IV, of 98% maximum rotation, when treated with a mixture of nitromethane and solid nitrosyl hexafluorophosphate at 0°, gave (75%) (+)-(/?)-! of 97% maximum rotation. Sulfoximide (-)-(i?)-IV, when treated with cold sodium hypochlorite, gave (-)-(R)-jV-chloromethyl-p-tolylsulfoximide ((-)-(R)-V). The absolute configuration of (+)-(i?)-I is already known, and those of (-)-(/?)-III and (-)-(i?)-IV were determined by X-ray methods. The absolute configuration of (-)-( 5)-II was established by comparison of the melting point composition diagram of (-)-II and (-)-III, and of (+)-II and (-)-III. Clearly the nucleophilic substitution reactions at sulfur, (-f)-I (-)-II, proceed with inversion, and the electrophilic, (+)-I -(-)-III and (-)-II (-)-III, proceed with retention of configuration, as does (-)-IV -* (+)-I. Optical rotatory dispersion curves of (+)-I, (-)-II, (-)-III, and (-)-IV exhibit well-defined Cotton effects, and these are correlated with their configurations. In the conversion of (+)-I to (-)-II the same reagent appears to donate an imide group and accept an oxygen atom, and thus it is concluded that the sulfur, oxygen, and nitrogen must be included in a ring system that is part of the same transition state and possibly the same intermediate. Kinetic studies of the reaction indicate it to be second order in concentration of the sulfur diimide reagent. Thus, the ring system cannot be any more than six-membered, which is much too small to accommodate a linear arrangement of incoming and leaving groups. An intermediate is proposed that accommodates all data in which the incoming and leaving groups occupy the equatorial positions of a trigonalbipyramid intermediate rather than the classical axial positions. Maps are developed that identify the stereochemical courses of associative substitution reactions on tetrahedra that form trigonal bipyramids and square pyramids capable of undergoing pyramidal reorganization. (1969).