Ruthenium catalysis alkenylation

Aromatic imines can be ortho-arylated and alkenylated using ruthenium catalysis (Equation (129)).1... 

Subsequently, the ruthenium-catalysed alkenylation of various acrylates was accomplished with alkenyl halides [62]. Most effective catalysis was achieved with [Ru(COD)(COT)] (98) as catalyst and NEts as base in the absence of additional solvent. Interestingly, both alkenyl bromides and chlorides could be employed as electrophiles (Scheme 10.35). When using an alkenyl chloride, the catalytic activity could be improved through the addition of P(p-C6H4p)3 (99) as ligand. The efficiency of this ruthenium catalyst in the alkenylation of /3-chlorostyrene (21) compared favourably with that observed for either Pd(OAc)2 or Pd(OAc)2/P(o-Tol)3 as catalysts. With respect to the working mode of the catalyst, a radical mechanism was shown to be less likely. Instead, Mitsudo et al. [62] proposed an initial oxidative addition of the alkenyl halide to a ruthenium(O) species followed by insertion of the alkene and )8-hydride elimination, all in analogy to palladium-catalysed processes. 

A nitrogen atom in heteroarenes such as azoles and pyridine also acts as good anchor in directed alkenylation. The authors reported the alkenylations of phenylpyrazoles, -imidazole, and -pyridine [36]. Depending on the ratio of substrates employed, mono- and diaUcenylated products can be obtained selectively. Using the procedure, one-pot synthesis of unsymmetrically substituted 1,3-dialkenylbenzene derivatives was achieved (Scheme 18.36). In contrast to the cases using a Rh catalyst, monoalkenylated phenylpyrazoles are formed predominantly under ruthenium catalysis, even in the presence of excess alkenes [37]. 

Under ruthenium catalysis, oxidative coupling of a,a-disubstituted benzy-lamines with acrylates can be performed efficiently at room temperature to produce (isoindol-l-yl)acetic acid derivatives (Eq. (7.48)) [58]. The reaction takes place accompanied by free amino group-directed orffio-alkenylation and successive intramolecular cyclization. 

The formation of allenylidene derivatives from ethynyl-hexanol and alkenyl-vinylidene mononuclear complexes (9), the formation of mononuclear ruthenium allenyl complexes from terminal alkynes (10), the intermediacy of ruthenium-allenylidene complexes in forming propargylic alcohols (II), and in the cyclization of propargyl alcohols (12), and the use of mononuclear ruthenium compounds in allylic alkylation catalysis (13) have also been reported. 

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