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2.1.1.1.1.4 Using 8-Hydroxyquinoline 1-Oxide as a Ligand

DOI: 10.1055/sos-SD-208-00004

Tomás-Gamasa, M.Science of Synthesis: Cross Coupling and Heck-Type Reactions, (2013215.

Despite the utility of the catalysts described in the previous sections, significant challenges remain to be overcome in this area. For example, it should be noted that copper-catalyzed N-arylation reactions rarely take place with copper loadings below 1 mol% and in some instances rather large quantities of ligand are required. In addition, from an economical point of view, it would be highly desirable to use aryl chlorides in Ullmann C—N coupling reactions. In this direction, 8-hydroxyquinoline 1-oxide (7) has become a ligand of choice. In 2011, Jiang and co-workers reported a protocol for the cross coupling of aryl halides with primary aliphatic amines or cyclic secondary amines. This method for producing arylamines 8 is very attractive from synthetic and practical points of view as the reactions take place with relatively low catalyst loading (1 mol% of CuBr) and under mild conditions. The catalytic system can also be used to promote highly efficient C—N bond-forming reactions from inexpensive aryl chlorides (Scheme 5).[‌28‌] However, very long reaction times are required, which may be problematic for some applications. Thus, for fast transformations, diol and amino acid ligands may be preferable to 8-hydroxyquinoline 1-oxide (7).

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Me8 M M8 M8 Meee (°M) Meee (e) Meeeee (%) Mee
8-M8MM8M8 M M Me 88 88 88 [‌88‌]
8,8-Me8M8M8 M M MM8MMMM8 88 88 88 [‌88‌]
8-MeM8M8 M M (MM8)8Me 88 88 88 [‌88‌]
8-Mee Me M (MM8)8MM 88 88 88 [‌88‌]
8-M8MM8M8 Me (MM8)8 888 88 88 [‌88‌]

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M-Meeeeeeeee 8; Meeeeee Meeeeeeee:[‌88‌]

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