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 obtai...
Sulfur-based protecting groups for pyrroles and the facile deprotection of 2-(2,4-dinitrobenzene)sulfinyl and sulfonyl pyrroles.
[reaction: see text] The effectiveness of simple sulfinyl and sulfonyl groups as electron-withdrawing protecting groups for pyrroles has been analyzed using (13)C NMR spectroscopy and confirmed by consideration of X-ray crystal structures. Additionally, the 2,4-dinitrobenzenesulfinyl and sulfonyl groups are shown to be effective electron-withdrawing protecting groups for pyrroles, and they can be removed by treatment with benzene thiol or thiolate under mild and specific conditions.
Vanadium-catalyzed asymmetric oxidations
Chirally modified vanadium complexes have been used as catalysts in enantioselective epoxidations of allylic alcohols and asymmetric sulfide to sulfoxide oxidations. For both reactions various combinations of chiral ligands and vanadium sources have been tested. The results of previous work and those of current investigations are discussed and details of the catalysis with respect to enantioselectivity and catalyst turnover is presented.