title: Chemoselective Pd-catalyzed oxidation of polyols: synthetic scope and mechanistic studies.
abstract: The regio- and chemoselective oxidation of unprotected vicinal polyols with [(neocuproine)Pd(OAc)]2(OTf)2 (1) (neocuproine = 2,9-dimethyl-1,10-phenanthroline) occurs readily under mild reaction conditions to generate α-hydroxy ketones. The oxidation of vicinal diols is both faster and more selective than the oxidation of primary and secondary alcohols; vicinal 1,2-diols are oxidized selectively to hydroxy ketones, whereas primary alcohols are oxidized in preference to secondary alcohols. Oxidative lactonization of 1,5-diols yields cyclic lactones. Catalyst loadings as low as 0.12 mol % in oxidation reactions on a 10 g scale can be used. The exquisite selectivity of this catalyst system is evident in the chemoselective and stereospecific oxidation of the polyol (S,S)-1,2,3,4-tetrahydroxybutane [(S,S)-threitol] to (S)-erythrulose. Mechanistic, kinetic, and theoretical studies revealed that the rate laws for the oxidation of primary and secondary alcohols differ from those of diols. Density functional theory calculations support the conclusion that β-hydride elimination to give hydroxy ketones is product-determining for the oxidation of vicinal diols, whereas for primary and secondary alcohols, pre-equilibria favoring primary alkoxides are product-determining. In situ desorption electrospray ionization mass spectrometry (DESI-MS) revealed several key intermediates in the proposed catalytic cycle.
authors: Department of Chemistry, Stanford University, Stanford, California 94306, USA.
authors: Kevin
authors: K
authors: Chung
authors: Steven M
authors: SM
authors: Banik
authors: Antonio G
authors: AG
authors: De Crisci
authors: David M
authors: DM
authors: Pearson
authors: Timothy R
authors: TR
authors: Blake
authors: Johan V
authors: JV
authors: Olsson
authors: Andrew J
authors: AJ
authors: Ingram
authors: Richard N
authors: RN
authors: Zare
authors: Robert M
authors: RM
authors: Waymouth
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D002384:Catalysis; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000438:Alcohols; D007659:Ketones; D009942:Organometallic Compounds; D010165:Palladium