Directing group 4-pyridyl

Silylation of benzyl C-H bonds using hydrosilanes can also be performed with the aid of Ru3(CO)12-catalyst (Table 1) [9]. This silylation occurs only at benzylic CH3 groups. Pyridine, pyrazole, and hydrazones function as good directing groups. Benzylamines, oxime ethers, dimethylanilides, and aryl pyridyl ethers have no activity in this silylation. 

This chelation-assisted C-H/olefin and C-H/acetylene coupling can be applied to a variety of aromatic compounds with a directing group such as ester, aldehyde, imine, azo, oxazolyl, pyridyl, and nitrile [7]. In this section, we describe the coupling reactions of aromatic carbonyl compounds with olefins using a transition metal catalyst. 

Itami, Yoshida and co-workers demonstrated that this methodology can also be employed in the intermolecular variant of the PK reaction.25 They showed that using a dimethyl(2-pyridyl)silyl group as a directing group allows the reaction to proceed catalytically with respect to the metal complex and gives some control over the regioselective outcome of the reaction. 

Substituted derivatives are lithiated in the 5-position. Exceptions to this are the pyridyl and 2-oxazolinyl groups the a-directing ability of the sulfur in thiophene is superior to other ortho-directing groups, e.g. ... 

In ruthenium-catalyzed direct arylations, the directing abilities of 2-oxazolinyl, 2-imidazolinyl, and 1-pyrazolyl groups turned out to be comparable to those observed for 2-pyridyl substituents [60]. As a consequence, a number of nitrogen-containing five-membered heterocycles have been employed as directing groups in intermo-lecular ortho-arylation reactions [60, 62], As an example, the 2-aryloxazoline 76 was... 

In 2001, Oi and Inoue [10a] reported a ruthenium-catalyzed C-H arylation with aryl halides, which utilized a 2-pyridyl group as directing group. For example, they found that 2-phenylpyridine can be reacted with an equimolar amount of... 

Examples of the C-H/C-H homocoupling of simple arenes have remained limited because of their low reactivity and poor selectivity. However, the reactivity and selectivity of these C-H/C-H coupling methods can be enhanced by directing groups (Scheme 17.41). In 2006, Sanford [196a] reported that a C-H/C-H homocoupling of 2-pyridyl-substituted (hetero)arenes can be promoted by catalytic Pd(OAc)2 and oxone in i-PrOH. 

It was independently reported by Gomez Arrayas and Carretero [22] and by Zhang [23] that a (2-pyridyl)sulfinyl group is utiUzable as a removable directing group to induce regioselective alkenylation (Scheme 18.23). Gomez Arrayas and Carretero [24] also reported a similar alkenylation of N-(2-pyridyl)sulfonyl anilines (Scheme 18.24). 

Secondary arylsulfonamides [65] and arylamides [66], as well as pyridyl sulfones [67], were also found to be effident directing groups in the C-H alkylation of... 

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