Sulfur inversion

The cis- and frans-sulfoxides (551) and (552) have been O-methylated with Meerwein s reagent. Reaction of the methoxy derivative with MeMgBr proceeds with inversion of configuration (Scheme 211) (74JA8026). The stereochemical course of the interconversions of sulfoxide, sulfimide and sulfoximide in the 2,3-dihydrobenzo[6]thiophene series has been investigated (73JA1916). The reaction cycle (Scheme 212) involves both nucleophilic and electrophilic substitution at chiral sulfur. Inversion of configuration takes place in the conversion of (553) to (554) in pyridine. 

Substitution at certain unsaturated centers has little direct stereochemical interest, because there is no choice, e.g. substitution at aromatic, acetylenic, and carbonyl carbons must go with retention. On the other hand, stereoselection is possible at ethylenic and allenic carbon, phosphorus (P—O, P=S) and sulfur (S=0) centers. There appear to be important mechanistic differences between substitutions at unsaturated carbon and phosphorus or sulfur. All SE, SH, SN substitutions at such carbon atoms appear to proceed in at least two steps, while those at phosphorus and sulfur may go in one or more steps. For the SN process, comparative data are available here, substitution at unsaturated carbon proceeds with retention, while at phosphorus and sulfur inversion predominates. Substitution at unsaturated phosphorus and sulfur sites was sufficiently similar to other saturated centers that it was considered with them. Because of these mechanistic differences, we shall examine substitutions at unsaturated carbon more closely. 

Figure 17.6 Sulfur inversion process in methionine-platinum complexes.

Gurnmin, D. D., Ratilla, E. M. A. and Kostic, N. M. (1986) Variable-temperature platinum-195 NMR spectroscopy, a new technique for the study of stereodynamics, sulfur inversion in a platinum(II) complex with methionine. Inorg. Chem., 25, 2429-2433. 

Detailed structural, spectroscopic, and computational studies on [Ru([n]aneS4)(2,2 -bipyridyl)][PF6]2 have concluded that the conformations of the macrocycles are determined by steric rather than electronic effects in these crowded cations and that the dynamic processes in solution previously attributed to reversible dissociation are in fact because of pyramidal sulfur inversion. ... 

Oki, M., Yamada, Y. and Murata, S., Sulfur inversion in and molecular-structure of meso-3,4-diethyl-3,4-dimethyl-l-phenylthiolaniumtetrafluoroborate, Bull. Chem. Soc. Jpn. 61 (3), 707-714 (1988). 

Sulfur inversions in trans-[PdX2L2 (X = Cl or Br L = (12), (13), or (14) have been investigated by vt NMR spectroscopy up to pressures of 220 MPa. Activation volumes A are very small in each case, indicating no dissociative or associative character, or solvent (CH2CI2 or CHCI3)... 

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