Assisted Direct Arylations of Arenes

An alternative approach to ensure selective monoarylations of ketimines, including those without meta-substituents, was based on the development of a novel catalytic system. Significant progress was achieved with air-stable (heteroatom-substituted) secondary phosphine oxides (HA)SPOs, since these preligands gave rise to arylation reactions also with less reactive, yet inexpensive, aryl chlorides as electrophiles. Here, the sterically hindered derivative (l-Ad)2P(0)H (54) was found 

Fewer examples of direct arylations of aldimines have thus far been reported. Aldimines with N-(2-pyridyl) substituents displayed a unique reactivity, in that the 

The problem of achieving selective monoarylations of 2-arylpyridines was solved by applying a sterically hindered diaminophosphine oxide (72) as preligand [60]. This air-stable preligand allowed the use of tosylates as electrophiles, which are easily 

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 

Selective ruthenium-catalyzed mono- or diarylation of 2-phenylpyridine (58). 

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