Palladium-Catalyzed Alkoxylation of N-Methoxybenzamides via Direct sp² C−H Bond Activation

Abstract

The palladium-catalyzed ortho-alkoxylation of N-methoxybenzamides has been demonstrated. With the CONHOMe group as a directing group, the aromatic C-H bond can be functionalized efficiently to generate ortho-alkoxylated derivatives in moderate to good yields.

Redox-Induced Aromatic C–H Bond Functionalization in Metal Complex Catalysis from the Electrochemical Point of View

“…Thus, it is obvious that such weak oxidants as oxygen (−0.78 to −1.26 V), 1,4-benzoquinone (0.16 to −0.875V) are not able to oxidize many palladacycles even up to Pd(III) (~0.25 to 1.4 V) complexes, the more so to Pd(IV) (~1.0 to 1.6V) [25]. This explains the numerous failed attempts to use them in such Pd-catalysed C-H functionalizations, such as 1,4-benzoquinone [27][28][29]75,[82][83][84][85], and O 2 [77,82,[86][87][88] for example.…”

“…To form the products under reductive conditions, the palladacycles need to be treated with strong reducing agents, rather than strong oxidants, which actually work here (PhI(OAc)2, K2S2O8, or oxone). Some other unproven assumptions about the possible pathways that are based on Pd(II)/Pd(0) shuttle [77] in the presence of strong oxidants, such as PhI(OAc)2, also seem to be unlikely. Based on the literature data [58], where the reduction potential of PhI(OAc) 2 is −1.29 V (vs. Fc + /Fc) or −0.91 V (vs. SCE) ( Table 2), it should be recognized as a very weak oxidant or even a mild reductant (Table 1).…”

“…To form the products under reductive conditions, the palladacycles need to be treated with strong reducing agents, rather than strong oxidants, which actually work here (PhI(OAc) 2 , K 2 S 2 O 8 , or oxone). Some other unproven assumptions about the possible pathways that are based on Pd(II)/Pd(0) shuttle [77] in the presence of strong oxidants, such as PhI(OAc) 2 , also seem to be unlikely. Inorganics 2017, 5, 70 9 of 17 Scheme 7.…”

Palladium-catalysed hydroxylation and alkoxylation

“…The group of Wang reported on the alkoxylation of aromatic C-H bonds using N-methoxyamides as directing group (Scheme 25). 49 After exploration of the reaction conditions (e.g., solvents, oxidants), the best system was found to be a combination of catalytic amounts of Pd(OAc) 2 (5 mol%) and K 2 S 2 O 8 in a mixture of dioxane and an alcohol, which was applied as an alkoxylation reagent. After having set up suitable reaction conditions, more than 20 different aromatic substrates containing the N-methoxyamide functionality were converted to the corresponding ethers.…”

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.…”