Buchwald ligands

Thiazole /V-oxides are also highly reactive substrates in direct arylation [80]. For example, the direct arylation of several thiazole /V-oxides with arylbromides in the presence of a palladium catalyst and a Buchwald ligand can be achieved at 25 °C,... 

Imidazole /V-oxide substrates may be used in a similar fashion. Initial investigations revealed that the use of palladium acetate in conjunction with an electron deficient 4-fluorophenylphosphine in acetonitrile at 70 °C provides C2 arylation in high yields. With the goal of achieving the same reactivity at or near room temperature it was determined that the use of palladium acetate in conjunction with a Buchwald ligand, catalytic copper bromide and 30 mol% pivalic acid in acetonitrile could also achieve high yields of C2 arylation at 25 °C. As was the case with thiazole V-oxides. if the C2 and C5 positions of the imidazole are blocked C4 arylation may also be achieved in synthetically useful yield (Scheme 15). 

A. Ghosh developed an efficient protocol for the arylation of oxazolidinones 72 which uses Buchwald ligands L4.112 Meta and ortho methoxy aryl chlorides gave low yields in the cross-coupling, whereas most other aryl chlorides gave excellent yields of the. W-aryl oxazolidinone 73, even with base sensitive functionality present on the aryl chloride. 

In 2004, Sadighi [48] reported that pyrrole anion 48 can be coupled at its C2 position with just an aryl bromide in scheme 17.11 in the presence of stoichiometric ZnClj and catalytic PdjOAcjj/Buchwald ligand 51 to form products such as 50 in... 

Daugulis [67] reported a palladium-catalyzed C-H arylation of heteroarenes with aryl chlorides. Although a number of methods of direct arylation of five-membered heteroarenes with aryl halides, including less reactive aryl chlorides, had been reported, thus, the direct arylation of N-substituted indoles, pyrroles, and furans with aryl chloride had been elusive except for Ohta s work [5]. Ohta s group succeeded in the C-H arylation of such heteroarenes with aryl chlorides using a combination of Pd(OAc)2, a bulky Buchwald ligand, and inorganic bases (Scheme 17.14). 

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