Annulation ruthenium-catalysed

Ruthenium-catalysed oxidative annulations of alkynes (55) to benzamides (54), involving the CH activation, has been developed as a new method for the synthesis of l(2//)-isoquinolones (56). Mechanistic studies provided strong evidence for a rate-limiting CH bond metallation, assisted by the orf/zo-amide group. 

Oxidative annulations reaction of alkynes is one of the important methods to synthesize fused polycyclic heteroarenes [169-173]. Whereas the above examples show easy ruthenium catalysed insertions of alkynes into aromatic sp C-H bonds efforts have been made with related catalysts to perform the double insertion of alkynes into C-H and heteroatom-hydrogen bonds as a route to a variety of heterocycles. Chae S. Yi, has first shown, using ruthenium(ll) catalyst precursors [RuH(CO)(PCy3)2(NCMe)2]BF4 and preferably Ru3(CO)i2/NH4PF6, the alkenylation and double insertions of alkynes into C-H and N-H bonds for the transformation of indolines with terminal alkynes into quinoline derivatives [(Eq. 86)] [174, 175]. 

Cheng recently explored an efficient method to synthesize substituted isoquinolinium salts from the one pot ruthenium-catalysed annulation with alkynes of in situ generated aldimines, from benzaldehydes and amines. [RuCl2(p-cymene)]2/AgBF4 catalyst associated with the oxidant Cu(BF4)2.6H20 (2 equiv.) at 110°C, led to isoquinolinium salts. The postulated five-membered cationic ruthenacycle intermediate was isolated in that case [(Eq. 98)] [188]. 

Abstract The selective catalytic activation/functionalization of sp C-H bonds is expected to improve synthesis methods by better step number and atom economy. This chapter describes the recent achievements of ruthenium(II) catalysed transformations of sp C-H bonds for cross-coupled C-C bond formation. First arylation and heteroarylation with aromatic halides of a variety of (hetero)arenes, that are directed at ortho position by heterocycle or imine groups, are presented. The role of carboxylate partners is shown for Ru(II) catalysts that are able to operate profitably in water and to selectively produce diarylated or monoarylated products. The alkylation of (hetero)arenes with primary and secondary alkylhalides, and by hydroarylation of alkene C=C bonds is presented. The recent access to functional alkenes via oxidative dehydrogenative functionalization of C-H bonds with alkenes first, and then with alkynes, is shown to be catalysed by a Ru(ll) species associated with a silver salt in the presence of an oxidant such as Cu(OAc)2. Finally the catalytic oxidative annulations with alkynes to rapidly form a variety of heterocycles are described by initial activation of C-H followed by that of N-H or O-H bonds and by formation of a second C-C bond on reaction with C=0, C=N, and sp C-H bonds. Most catalytic cycles leading from C-H to C-C bond are discussed. 

C-H bonds for C-C cross-couplings and annulation reactions. These ruthenium (II) catalysed cross-coupling reactions from C-H bonds have been recently presented in reviews [47, 48, 58]. Consequently, after a short presentation of the original examples this chapter will describe recent ruthenium(II) catalysed functionalization of sp C-H bonds and C-C bond formations, including the examples reported till the end of 2013, and discuss some catalytic mechanism aspects. 

Various pyrroles were synthesized through the ruthenium(II)-catalysed oxidative annulation of enamines with aryl- and alkyl-alkynes in r-AmOH with only 30 mol% of Cu(0Ac)2.H20 under ambient air conditions. Numerous functional groups including ester, vinyl, bromo, nitro substituents and heteroaromatic were tolerated in this catalytic system [(Eq. 96)] [184]. 

Hydroxy directing groups such as in naphthols, 4-hydroxycoumarin and 4-hydroxy-substituted quinolin-2-one were found to promote the formation of fluorescent pyrans via ruthenium(II) catalysed annulation with alkynes by addition of 2 equiv. of Cu(0Ac)2.H20 as the oxidant The competition results revealed that electron-deficient alkynes favour this reaction (Scheme 22) [193],... 

NHC-Ru(II) complexes have been recently shown by Pinjing Zhao to perform the catalysed [3+2]carbocyclizations of alkynes with aromatic N-H ketimines [(Eq. 105)] [197]. The ruthenium(II) catalyst is based on jt-allyl precursor [(cod) Ru(q -methallyl)2] with addition of an NHCarbene as ligand, which is necessary for the reaction to take place and to occur at room temperature. Thus this catalyst significantly decreased this [3+2] annulation temperature. It is noteworthy that the C-H bond at the more electron-deficient arene favoured this reaction in non-polar solvents. 

---