A re-investigation of Modena’s protocol for the asymmetric oxidation of prochiral sulfides

Enantioselective oxidation of sulfides with H2O2 catalyzed by a pre-formed manganese complex

A facile and environmentally friendly method is presented for the asymmetric oxidation of sulfides with H₂O₂ by an in situ-formed manganese complex, affording the corresponding chiral sulfoxides in high yields and excellent enantioselectivities.

Sulfoxides in the allylation of aldehydes in the presence of silicon tetrachloride and allyltributylstannane

SiCl4 can be conveniently activated by catalytic amounts of dimethyl sulfoxide or other readily-available sulfoxides for the allylation of aromatic, hetero-aromatic and unsaturated aldehydes in the presence of allyltributyl stannane. Chiral aryl methyl sulfoxides have been used to develop asymmetric allylation methods, as well as probe the aldehyde substrate scope.

Asymmetric oxidation of 2-(arylsulfenyl)pyrroles

The asymmetric oxidation of prochiral 2-(arylsulfenyl)pyrroles has been investigated. A marked electronic effect within the substrate significantly influenced the degree of enantioselectivity obtained, with very high enantio selectivity being obtained for 5-(nitrobenzensulfenyl)pyrrole-2-carboxaldehydes using Ti(i-PrO)4/(+)-(R,R)-DET/H2O/CHP. This result bodes well for optimizing the asymmetric oxidation of other diaryl sulfides, substrates that have previously given only low enantiomeric excesses.Key words: asymmetric oxidation, sulfide, sulfoxide, pyrrole.

Iron-Catalyzed Oxidation of Thioethers by Iodosylarenes: Stereoselectivity and Reaction Mechanism

Catalytic properties of a series of iron(III)-salen (salen=N,N'-bis(salicylidene)ethylenediamine dianion) and related complexes in asymmetric sulfoxidation reactions, with iodosylarenes as terminal oxidants, have been explored. These catalysts have been found to efficiently catalyze oxidation of alkyl aryl sulfides to sulfoxides with high chemoselectivity (up to 100 %) and moderate-to-high enantioselectivity (up to 84 % with isopropylthiobenzene and iodosylmesitylene), the TON (TON=turnover number) approaching 500. The influence of the ligand (electronic and steric effects of the substituents), oxidant, and substrate structures on the oxidation stereoselectivity has been investigated systematically. The structure of the reactive intermediates (complexes of the type [Fe(III)(ArIO)(salen)] and the reaction mechanism have been revealed by both mechanistic studies with different iodosylarenes and direct in situ (1)H NMR observation of the formation of the reactive species and its reaction with the substrate.