Ruthenium-Catalyzed Ortho-Selective C–H Alkenylation of Aromatic Compounds with Alkenyl Esters and Ethers

Abstract

A direct, regioselective alkenylation of aromatic C–H bonds of aryl- and heteroarylpyridines and related compounds with alkenyl esters was developed using Ru(cod)(cot) as a catalyst. Aromatic compounds bearing electronically diverse substituents and various heterocyclic directing groups are reacted with alkenyl acetates bearing mono- and disubstituted alkenyl groups with aliphatic and aromatic substituents to give ortho-alkenylation products in high yields. The results of deuterium-labeling experiments and competition reactions using different ratios of the E and Z isomers of β-styryl acetate suggested that the C–H alkenylation proceeded via a ruthenium–alkene intermediate and the C–O bond of the alkenyl acetate was cleaved by β-acetoxy elimination. Two types of catalytically relevant species were identified, and the reactivities of these species, combined with the results of the kinetic studies, suggest that the rate-limiting step is the exchange of the COD ligand with the alkenyl ester. On the basis of the elucidated mechanism, the first catalytic coupling reaction using aromatic C–H bonds with C–O bonds of ethers was also developed.

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

“…In 2013, Ackermann and co-workers reported the Ru(II) catalyzed arylation/alkylation of 2-aryl pyridines (3) with secondary alkyl halides (36) to produce meta-alkylated products (37) with 33-62% yields (Scheme 17). [31] Ruthenium(II)biscarboxylate complexes are essential for the direct meta-alkylations reaction.…”

“…[35] In 2014, Kakiuchi et alreported alkenylation reactions of 2-aryl pyridines with the alkenyl esters using Ru(cod)(cot) as a catalyst. [36] The reaction was performed on various 2-aryl pyridi < nes (3) and related aromatic compounds with a variety of alkenyl esters (44) including 1-or 2-monosubstituted and 1,2-or 2,2-disubsituted vinyl esters to obtain the alkenylated products (45) (Scheme 21). The alkenylation takes place selectively at the g-C À H bond to nitrogen atom of the directing group.…”

Recent Advances in C–H Bond Functionalization with Ruthenium-Based Catalysts

“…Ruthenium-catalysed alkenylation of phenyloxazolines with alkenes.Alkenyl esters and ethers were also successfully used in the alkenylation of 2-phenylpyridine derivative in the presence of ruthenium(0) catalyst [Ru(COD)(COT)] in xylene at 150 • C, affording exclusively monoalkenylated product[108]. In 2013, Ackermann and Ma demonstrated the ruthenium-catalysed oxidative C-H bond alkenylation of 2-phenoxypyridine possessing a removable directing group[109].…”

CH Alkenylations with Alkenyl Acetates, Phosphates, Carbonates, and Carbamates by Cobalt Catalysis at 23 °C

“…It is noteworthy that the only arene alkenylation of non-acidic CÀH bonds [14] with alkenyl esters that has been reported thus far required the expensive ruthenium complex [Ru(cod)(cot)] and a reaction temperature of 120 8C. [15] We initiated our studies by probing various reaction conditions for the envisioned C À H alkenylation of indole 1 a [16] with alkenyl acetate 2 a ( Table 1). The use of phosphine ligands did not lead to significant conversion of the starting Scheme 1.…”