C–O Bonds from Pd‐Catalyzed C(sp³)–H Reactions Mediated by Heteroatomic Groups

Abstract

This review summarizes Pd‐catalyzed procedures leading to single C–O bonds from aliphatic C–H bonds of substrates bearing heteroatomic groups. Coordination of the latter to PdII species favors the activation of a C(sp3)–H bond and controls the regioselectivity, leading to a palladacycle as intermediate. Either PdII–Pd0 or PdII–PdIV redox catalytic cycles, possibly with a PdIII intermediate, might be involved, depending on the directing group and the oxidant.

Ligand-Enabled Monoselective β-C(sp3)–H Acyloxylation of Free Carboxylic Acids Using a Practical Oxidant

“…The distance between the hydroxyl and carboxylic acid functional groups has a remarkable effect on biological activity . It is therefore highly desirable to develop synthetic methods to selectively oxidize parent fatty acids. , Recent advances in the C­(sp 3 )–H activation of aliphatic acid derivatives represent a powerful approach to the direct oxidation of aliphatic acids at the β position (Scheme C) . However, these reaction protocols always require exogenous directing groups (DGs) to promote cyclometalation; thus, two or three additional steps are required to install and remove the DG. ,,,− Additionally, reported oxidants used in C–H oxidation are largely limited to hypervalent iodine reagents such as PhI­(OAc) 2 . ,− ,, Despite the early successes in β-arylations of free acids through the reactivity of sodium or potassium carboxylates, analogous acetoxylation reactions were only recently reported by van Gemmeren’s group .…”

Iron‐Catalyzed Ring‐Closing C−O/C−O Metathesis of Aliphatic Ethers

“…Following our continuous efforts to develop new catalytic isodesmic reactions, [9] we were interested in investigating whether two C(sp 3 ) À Ob onds could engage in ar ing-closing metathesis manifold. Owing to the ubiquity of aliphatic cyclic ethers,s uch as tetrahydrofurans and tetrahydropyrans,i na ll fields of chemistry, [10] we thought that the synthesis of these substrates through am etathesis strategy would complement traditional methods [11,12] for ether synthesis.Inparticular, the fact that two identical functional groups [13] (i.e., two ROR' groups) can be engaged in this reaction would reduce the overall number of synthetic steps compared to traditional methods,s uch as the Williamson ether synthesis, [14] which requires the separate pre-installation of two distinct functional groups (i.e., CÀBr and CÀO À )p rior to the etherification step.…”

Palladium(II)‐Catalyzed Sp3/Sp2γ‐ and δ‐C‐H Functionalization of Aryl Amines using 5‐Methylisoxazole‐3‐Carboxamide as Directing Group

“…After investigating the MICA‐aided γ ‐C(sp 3 )‐H arylation of 11 , we then intended to attempt the MICA‐aided γ ‐C(sp 3 )‐H acetoxylation of benzylic methyls of ortho ‐toluidines 11 under the Pd(II)‐catalyzed acetoxylation reaction conditions (Scheme ) . Accordingly, the γ ‐C(sp 3 )‐H acetoxylation of 11 a with the acetoxylating reagent PhI(OAc) 2 in the presence of the Pd(OAc) 2 catalyst and Ac 2 O/AcOH in toluene at 130 °C afforded the γ ‐C(sp 3 )‐H acetoxylated product 18 a (2‐aminobenzyl acetate) in 76% yield.…”