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Electron‐Deficient Alloxazinium Salts: Efficient Organocatalysts of Mild and Chemoselective Sulfoxidations with Hydrogen Peroxide
Author(s) -
Ménová Petra,
Dvořáková Hana,
Eigner Václav,
Ludvík Jiří,
Cibulka Radek
Publication year - 2013
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201300617
Subject(s) - chemistry , trifluoromethyl , catalysis , hydrogen peroxide , perchlorate , thioanisole , substituent , salt (chemistry) , medicinal chemistry , sulfone , organic chemistry , inorganic chemistry , ion , alkyl
A series of substituted alloxazinium perchlorates has been prepared and tested as catalysts for the oxidation of sulfides to sulfoxides with hydrogen peroxide. The logarithms of the observed rate constants of thioanisole oxidation correlate with the Hammett σ constants of the substituents on the alloxazinium catalysts, as well as with their reduction potentials E 0′ and their p K R+ values, representing the alloxazinium salt/pseudobase equilibrium. The stronger the electron‐withdrawing substituent, the more efficient is the alloxazinium catalyst. The alloxazinium salts with a cyano or trifluoromethyl group in position 8 proved to be the most efficient, operating at room temperature at small loadings, down to 0.1 mol%, achieving turnover number values of up to 640 and acceleration by a factor of 350 relative to the non‐catalyzed oxidation. The 8‐cyanoalloxazinium perchlorate was evaluated as the best catalyst; however, due to its relatively good accessibility, the 8‐(trifluoromethyl)alloxazinium perchlorate seems to be the catalyst of choice for sulfoxidations with hydrogen peroxide. It was successfully tested for the sulfoxidation of a series of aliphatic and aromatic sulfides on a preparative scale. It produced the corresponding sulfoxides in quantitative conversions and with high isolated yields (87–98%). No over‐oxidation to sulfone was ever observed.