Oxidative cyclizations 2- imidazole pyridines

Analogous high-yield cyclizations were reported with l-amino-2-nitro-derivatives of pyridines and isoquinolines, which gave the corresponding furoxans [53,54], Anilines oxidized in the presence of indoles afforded Schiff s bases from 2- and/or 3-position in low yield [55], An unexpected rearrangement occurred on treatment of l-phenyl-4-methyl-5-aminopyrimidinone with DIB and catalytic amounts of nickel dichloride, resulting in the formation of an imidazole derivative [56] ... 

Meutermans and Alewood [48] reported the solid-phase synthesis of tetrahydroisoquinolines 13 and dihydroisoquinolines 13a using the Bischler-Napieralski reaction (Fig. 5). The polystyrene resin-bound deprotected L-3,4-dimethoxyphenylalanine was acylated with acetic acid derivatives using N- [(IH-benzotriazol-1 -yl)(dimethylamino)methylene] -iV-methylmethana-minium hexafluorophosphate A-oxide (HBTU) as a coupling reagent. The product obtained was then treated with phosphorus oxychloride under optimized conditions to afford a Bischler-Napieralski cyclization. Hutchins and Chapman [49] reported the synthesis of tetrahydroisoquinolines 13b and 4,5,6,7-tetrahydro-3H-imidazol[4,5-c]pyridines 14 via cyclocondensation of the appropriate dipeptidomimetic with various aldehydes (Fig. 6). 

Interestingly, this Heck-type palladium-catalyzed oxidative addition/insertion manifold can also be applied to the actual formation of the carbon-heteroatom bond. This was illustrated by Narasaka in the reaction of olefin-tethered oxime derivatives. This chemistry can be considered to arise from oxidative addition of the N—O bond to palladium (30) followed by the more classical olefin insertion and (3-hydride elimination, ultimately allowing the assembly of pyrroles (Scheme 6.58) [79]. The nature of the OR unit was found to be critical in pyrrole formation, with the pentafluorobenzoylimine leading to selective cyclization and rearrangement to the aromatic product. An analogous approach has also been applied to pyridines and imidazoles [80]. 

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