Mechanism of the enantioselective oxidation of racemic secondary alcohols catalyzed by chiral Mn(III)-salen complexes.
The experiments described here clarify the mechanism and origin of the enantioselectivity of the oxidation of racemic secondary alcohols catalyzed by chiral Mn(III)-salen complexes using HOBr, Br(2)/H(2)O/KOAc or PhI(OAc)(2)/H(2)O/KBr as a stoichiometric oxidant. Key points of the proposed pathway include (1) the formation of a Mn(V)-salen dibromide, (2) its subsequent reaction with the alcohol to give an alkoxy-Mn(V) species, and (3) carbonyl-forming elimination to produce the ketone via a highly organized transition state with intramolecular transfer of hydrogen from carbon to an oxygen of the salen ligand.
Brown
M Kevin
MK
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Blewett
Megan M
MM
Colombe
James R
JR
Corey
E J
EJ
D000438:Alcohols / Q000737:chemistry*; D001965:Bromides / Q000737:chemistry; D002384:Catalysis; D005029:Ethylenediamines / Q000737:chemistry*; D007700:Kinetics; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D055672:Static Electricity; D013237:Stereoisomerism; D013379:Substrate Specificity
D000438:Alcohols; D001965:Bromides; D005029:Ethylenediamines; D009942:Organometallic Compounds; D008345:Manganese; C011452:disalicylaldehyde ethylenediamine