Oxidation of α-Keto Alcohols with Triphenylantimony Dibromide Participation of Pentavalent Antimony

Abstract

α-Keto alcohols were oxidized into α-diketones with triphenylantimony dibromide [2 a] in the presence of two equiv. of base. The oxidation is rationalized by the sequence involving the base-catalyzed ligand exchange at apical position from bromine to a-keto alcohol to give hypervalent antimony [D] or stibonium bromide [E] which is followed by deprotonation at carbinyl position to furnish a-diketone directly with loss of triphenylstibine (path 1) or via hypervalent antimony [F] (path 2) (Scheme 2). Treatment of tri(p-tolyl)antimony dibromide [2 b] with 2-pyridone and triethylamine afforded bis(2-pyridyloxy)tri-p-tolylsantimony (V) [2 d] which was more effective for the oxidation without additional base (Scheme 3).
Finally antimony-catalyzed debromination and oxidation cycle was devised for the sys tem of α-keto alcohols and 2, 3-dibromo-3-phenylpropionate (bromine donor) (Scheme 4).