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The Kharasch–Sosnovsky reaction is the radical oxidation of an allylic alkene to a allylic alcohol using a copper catalyst and a peroxy ester (e.g. tert-Butyl peroxybenzoate) or a peroxide. Chiral ligands can be used to render the reaction asymmetric, constructing chiral C–O bonds via C–H bond activation. This is notable as asymmetric addition to allylic groups tends to be difficult due to the transition state being highly symmetric. The reaction is named after Morris S. Kharasch and George Sosnovsky who first reported it in 1958.
Modifications
Substitutedoxazoline
Oxazoline is a five-membered heterocyclic organic compound with the formula . It is the parent of a family of compounds called oxazolines (emphasis on plural), which contain non-hydrogenic substituents on carbon and/or nitrogen. Oxazolines are the ...
s and thiazoline
Thiazolines (or dihydrothiazoles) are a group of isomeric 5-membered heterocyclic compounds containing both sulfur and nitrogen in the ring. Although unsubstituted thiazolines are rarely encountered themselves, their derivatives are more comm ...
s can be oxidized to the corresponding oxazole
Oxazole is the parent compound for a vast class of heterocyclic aromatic organic compounds. These are azoles with an oxygen and a nitrogen separated by one carbon. Oxazoles are aromatic compounds but less so than the thiazoles. Oxazole is a weak ...
s and thiazole
Thiazole, or 1,3-thiazole, is a heterocyclic compound that contains both sulfur and nitrogen. The term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular fo ...
s via a modification of the classic reaction.
Mechanism
The mechanism is believed to involve radical intermediates and copper in the I, II and III oxidation states, via the following steps: Cu(I) + BzO–O''t''Bu → Cu(II)–OBz + ''t''BuO• ''t''BuO• + CH2=CH–CH2R → ''t''BuOH + CH2=CH–CHR• CH2=CH–CHR• + Cu(II)–OBz → CH2=CH–CHR–Cu(III)–OBz CH2=CH–CHR–Cu(III)–OBz → CH2=CH–CHR(OBz) + Cu(I) The last step, a reductive elimination of an organocopper(III) intermediate to regenerate the Cu(I) catalyst and form the product, is proposed to take place via a seven-membered ring transition state.References
Catalysis Name reactions Carbon-heteroatom bond forming reactions {{reaction-stub