Enantioselective oxidation of sulfides catalyzed by titanium complexes of 1,2‐diarylethane‐1,2‐diols: Effect of the aryl substitution

Abstract

The effects of the substitution on the aryl moiety on the asymmetric oxidation of sulfides mediated by Ti-complexes of chiral 1,2-diarylethane-1,2-diols were investigated. The substitution of the aryl ring of the diol with both EWG and EDG substituents generally decreased the enantioselectivity with respect to the use of unsubstituted 1,2-diphenylethane-1,2-diol (1a). Only in the presence of 1,2-di(4-t-butyl)phenyl-1,2-diol (1g) were higher ee's obtained with aryl methyl and aryl benzyl sulfides affording ee's up to 90 and 99%, respectively. Lower ee's were achieved with larger naphthyl and aryl alkyl sulfides. Contrary to the other Ti-alcoholates used in the oxidation of sulfides, the Ti-complex of diol 1g was soluble in hexane, allowing us to perform the process with high enantioselectivity in this solvent, with great environmental advantages over the commonly used chlorinated solvents.

Selective and Practical Oxidation of Sulfides to Diastereopure Sulfoxides: A Combined Experimental and Computational Investigation

“…In particular, the last approach has been extensively investigated, being rather general, powerful, and suitable for scale‐up 16–19. The most common catalysts of this type are based on titanium complexes, but effective methods involving other transition metals (in particular vanadium) are well documented 14,16–26. Diastereomerically pure sulfoxides can be obtained by either submitting chiral sulfoxides to diastereoselective processes1–4 (which generates novel substrate stereogenic centers) or oxidizing chiral sulfides diastereoselectively 4,14.…”

Bicyclo[1.1.1]pentyl Sulfoximines: Synthesis and Functionalizations

“…For the enantioselective synthesis of sulfoximines we considered a route through enantioselective oxidation to the sulfoxide ( S4 ) . However, in all our attempts with chiral titanium complexes we obtained a racemic mixture of S4 .…”

Recent developments in enantioselective titanium-catalyzed transformations

“…Along with tartrates, other chiral 1,2-diols have also been successfully applied as ligands in this type of reactions [63]. For example in 2006, Cardellicchio described the use of chiral hydrobenzoin as ligand in asymmetric titanium-catalyzed sulfoxidations with tert-butyl hydroperoxide [64].…”