Pd‐Catalyzed Stereoselective Oxidation of Methyl Groups by Inexpensive Oxidants under Mild Conditions: A Dual Role for Carboxylic Anhydrides in Catalytic CH Bond Oxidation

Abstract

Unactivated CH3 groups in 2‐oxazolines are oxidized by inexpensive oxidants, such as tert‐butyl peroxyacetate and lauroyl peroxide, in the presence of a catalytic amount of Pd(OAc)2. Carboxylic anhydrides are essential for both the oxidation of the PdC bonds and regeneration of Pd(OAc)2. The use of [D6]Ac2O as the solvent shows that the acetyl group incorporated into the product is from acetic anhydride rather than the oxidant (see scheme).

Ruthenium(II)-catalyzed <I>Ortho</I> C-O Bond formation of Substituted Aromatics with Oxygen Nucleophiles through C-H Bond Activation

“…Several directing groups such as 2-pyridyl, carbonyl, ester, nitrile, carboxylic acid, N-acetyl and amide can be efficiently used for the reaction. With the assistance of these directing groups, acetoxylation (Henry, 1971;Yoneyama and Crabtree, 1996;Sanford et al, 2004;Yu et al, 2005;Yu et al, 2006;Corey et al, 2006;Wu et al, 2008;Chen et al, 2009;Cheng et al, 2010;Yu et al, 2010;Yu et al, 2011;Sanford et al, 2012;Kim et al, 2013), alkoxylation (Sanford et al, 2006;Wang and Yuan, 2010), hydroxylation (Yu et al, 2009;Dong et al, 2012) and benzoxylation (Sanford et al, 2005;Cheng et al, 2011) at the ortho C-H bond of directing group substituted aromatics with various oxygen nucleophiles have been studied. Palladium and copper complexes are efficient catalysts for this type of reaction.…”

Substrate‐Directed C‐H Functionalization of 2‐Aryl Pyridines by Transition Metal Complexes

“…In another method, Ru(II) has been used successfully for the direct arylation of 2-aryl pyridines (3)with aryl bromides (12) to give the corresponding arylated compounds (13) in NMP at 120 o C for 20 h(Scheme 5).…”

“…[1][2][3] A wide range of metal catalysts including palladium, [4] ruthenium, [5] rhodium, [6] cobalt, [7] and iridium [8] have been exploited in greater extent. Among them, metal-catalyzed oxidative functionalization of sp 2 and sp 3 CÀH bonds proceeds smoothly in the presence of directing groups such as pyridines, [9] amides, [10] carbamates, [11] oxazolines, [12] oximeethers, [13] and pyrimidines. [14] These ligand-directed CÀH functionalization reactions facilitate the formation of CÀC,CÀX,CÀN,CÀO, and CÀS bonds under mild conditions.…”

Coupling of Nitrogen Heteroaromatics and Alkanes without Transition Metals: A New Oxidative Cross‐Coupling at CH/CH Bonds

“…The N-oxides of other nitrogen heteroaromatics such as quinoline N-oxide derivative 1 h also react smoothly with 2 a (entry 8). It should be noted that the reaction always takes place on the oxygenated N-heteroaromatic ring leaving other aromatic rings on the substrate intact (entries 4,[6][7][8].…”

“…[1] Since the seminal work reported by Murai, [2] extensive research has been carried out on C À C bond formation through transition-metal-catalyzed C À H bond functionalization. [3,4] We [5] and others [6] have developed various methods to generate C À C bonds directly from two different C À H bonds (cross-dehydrogenative-coupling, CDC) in the presence of an oxidizing reagent and a transition metal. Since these reactions proceed best with activated CÀH bonds, including those of 1,3-dicarbonyls, alkynes, and nitroalkanes, such cross-coupling involving an unactivated sp 3 -hybridized C À H bond has been a challenging target.…”