Does It Occur at Oxygen or Nitrogen?

Acid catalyzed alcoholysis of sulfinamides: unusual stereochemistry, kinetics and a question of mechanism involving sulfurane intermediates and their pseudorotation

The synthesis of optically active sulfinic acid esters has been accomplished by the acid catalyzed alcoholysis of optically active sulfinamides. Sulfinates are formed in this reaction with a full or predominant inversion of configuration at chiral sulfur or with predominant retention of configuration. The steric course of the reaction depends mainly on the size of the dialkylamido group in the sulfinamides and of the alcohols used as nucleophilic reagents. It has been found that bulky reaction components preferentially form sulfinates with retention of configuration. It has been demonstrated that the stereochemical outcome of the reaction can be changed from inversion to retention and vice versa by adding inorganic salts to the acidic reaction medium. The unusual stereochemistry of this typical bimolecular nucleophilic substitution reaction, as confirmed by kinetic measurements, has been rationalized in terms of the addition-elimination mechanism, A-E, involving sulfuranes as intermediates which undergo pseudorotations.

IMPROVED SYNTHESIS OF 1-BENZENESULFINYL PIPERIDINE AND ANALOGS FOR THE ACTIVATION OF THIOGLYCOSIDES IN CONJUNCTION WITH TRIFLUOROMETHANESULFONIC ANHYDRIDE

An improved protocol for the large scale production of 1-benzenesulfinyl piperidine and other sulfinamides is described. It is demonstrated that 1-benzenesulfinyl pyrrolidine and N,N-diethyl benzenesulfinamide function analogously to 1-benzenesulfinyl piperidine in the trifluoromethanesulfonic anhydride-mediated activation of thioglycosides, and that their less crystalline nature enables them to be used at -78 °C as opposed to the -60 °C required to keep 1-benzenesulfinyl piperidine in solution. N,N-Dicyclohexyl benzenesulfinamide does not activate thioglycosides in combination with trifluoromethanesulfonic anhydride which is attributed to its greater steric bulk.

Selectivity in proton transfer, hydrogen bonding, and solvation

The site of protonation (or deprotonation) of polyfunctional bases and acids can be determined through the comparison of experimental NMR properties (chemical shift and relaxation rates) with the corresponding data calculated by quantum chemical methods. The results can be interpreted in terms of the competition between intrinsic base strengths and solvation. Qualitatively similar criteria are found to hold for hydrogen bonding. The selective enrichment in a cosolvent in the solvation shell of a solute dissolved in a solvent mixture (preferential solvation) can be determined through the analysis of intermolecular cross-peak intensities in NOESY spectra.