Oxidative Alkenylation of Aromatic Esters by Ruthenium-Catalyzed Twofold C–H Bond Cleavages

Abstract

Cationic ruthenium(II) complexes enabled catalytic twofold C-H bond functionalizations with weakly coordinating aromatic esters in a highly chemo-, site- and diastereo-selective as well as site selective fashion. The oxidative Fujiwara-Moritani-type alkenylation provided step-economical access to diversely substituted styrenes and proved viable in an aerobic manner. Mechanistic studies were indicative of a reversible acetate-assisted cycloruthenation step.

Solvent‐Free Ruthenium(II)‐Catalyzed C–H Activation: Synthesis of Alkenylarylpyrazole Derivatives

“…This is plausibly due to acetic acid that is in situ generated from Cu(OAc) 2 , as affirmed by HRMS analysis of 6j (see the Supporting Information) A similar phenomena was found in an earlier report. [45] On the other hand, the presence of any other aprotic solvent may suppress the release of acetic acid in the catalytic cycle.…”

Substrate‐Selective Catalysis

“…[{Ru( p ‐cymene)Cl 2 } 2 ] was also exploited as a pre‐catalyst in the oxidative C(sp 2 )H alkenylation of aryl carbamates105 and aromatic esters106 with alkenyl‐substituted esters in the presence of Cu(OAc) 2 ⋅H 2 O as the terminal oxidant and AgSbF 6 as promoter. The so‐formed active cationic catalyst displayed chemoselectivity and site selectivity in parallel with tolerance for a broad spectrum of substituents on the substrates.…”

“…[{Ru(p-cymene)Cl 2 } 2 ] was also exploited as a pre-catalyst in the oxidative C(sp 2 )ÀH alkenylation of aryl carbamates [105] and aromatic esters [106] with alkenyl-substituted esters in the presence of Cu(OAc) 2 [{Ru(p-cymene)Cl 2 } 2 ] also acted as a pre-catalyst in the hydroxyl-assisted oxidative annelations of internal symmetrical and unsymmetrical alkynes by a-naphthols, 4-hydroxycoumarin and 4-hydroxy-1-methylquinolin-2(1 H)-one, respectively, in the presence of Cu(OAc) 2 ·H 2 O as the terminal oxidant. [107] Interestingly, the annelation of unsymmetrical alkynes by a-naphthols occurred in excellent regioselectivities and high yields.…”

Palladium-Catalyzed ortho-Olefination of Phenyl Acetic and Phenyl Propylacetic Esters via C–H Bond Activation

“…11 In 2012, Ackermann and co-workers also reported a ruthenium (II) complex catalyzed oxidative olefination of arenes using weakly coordinated esters as directing groups. 12 Very recently, Yu and co-workers 13 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 significant progresses, developing an ester as directing group in assisted ortho-C-H transformation of phenylpropionic acid is still desirable. As functional group/directing group, esters are widely available and can be readily converted to amides, alcohols, or carbonyl compounds.…”