Azanickelacycles, formation

Azanickelacycle formation with partial replacement of the heterocyclic moiety substance by the nickel catalyst was also employed for the synthesis of indoles, an important class of heterocycles found in natural products and pharmaceuticals. Maizum et al. demonstrated a nickel-catalyzed decarbonylative cycloaddition by which anthranilic acid derivatives 39, which are readily available, react with alkynes to afford substituted indoles 41 (Scheme 12.17) [20]. The reaction is supposed to proceed via oxidative addition and decarbonylation to afford azanickelacycle 40, followed by alkyne insertion, 1,3-acyl migration, and reductive elimination, to afford A-pivaloyl-protected indole 41. Deprotected indole 42 was obtained as the final product upon workup, that is, treatment of the reaction crude reaction mixture with NaSMe in MeOH. 

The cycloaddition of alkenes is quite general and has been extended to the formation of azanickelacycles 12 by using isocyanates instead of CO2 in the reaction with alkenes or 1,3-butadienes (Eq. 6). These... 

This method also allows preparing azanickelacycles starting from unsaturated carboxamides. Thus, a,P-unsaturated primary and secondary amides lead to the formation of azametallacycles 34 (Eq. 16). =) ... 

The reaction of a N-dideuterated primary amide leads to the selective formation of dideuterated azanickelacycle 35 (Eq. 

Methylation of nickelacycle 30, obtained in the reaction between Ni(COD)(py)2 and 2-cyclopentencarboxylic acid, unexpectedly leads to the formation of cw-2-methylcyclopentanecarboxylic acid (Scheme 29) 33(0 pjijs product probably arises by methylation of isomeric nickelacycle 56, formed by 3-hydride elimination and insertion with the opposite regiochemistry. When the same reaction is carried out with a large excess of iodomethane, d.y-3-methylcyclopentanecarboxylic acid is obtained. Methylation reactions of related azanickelacycles have also been reported. ... 

Imine Alkynes Cyclization. Bu2MeP is the ligand of choice for the formation of 1,2-dihydropyridines by reaction of a sul-fonylimine with some alkynes. In stoichiometric conditions, the isolation of azanickelacycles intermediates was possible, but the reaction also proceeded catalytically giving directly the final dihydropyridine (eq... 

Oxidative addition of a low-valent nickel catalyst to a C—N bond yields a reactive intermediate C—Ni—N, which undergoes carboamination with an alkyne via simultaneous C—C and C—N bond formation. However, this type of transformation has not been explored in detail, despite its usefulness for the preparation of nitrogen-containing compounds, because the C—N bond is less reactive toward oxidative addition of transition metals than are C—O and C—S bonds. In this context, Kajita et al. found that oxidative addition of phthalimide 19 to Ni(0), followed by decarbonylation, yields azanickelacycle 20, which then reacts with alkynes to furnish isoquinolones 21 (Scheme 12.9) [12]. For example, the reaction of iV-pyridylphthalimide with 4-octyne successfully afforded isoquinolone derivative 22. iV-Pyrrolylphthalimides... 

In 2009, Miura et al. reported an elegant assembly of pyrroles 38 from alkynes and A-sulfonyl-1,2,3-triazoles 36 (Scheme 12.16) [18,19]. The reaction proceeded at 100 °C in the presence of a nickel catalyst and aluminum co-catalyst to afford substituted pyrroles 38. It is worth mentioning that the starting material 36 can be produced readily by the copper-catalyzed azide-alkyne Huisgen cycloaddition. The reaction is thought to be initiated by tautomerization of the triazole to an a-iminodiazo compound, which reacts with Ni(0) to give a nickel carbenoid and then the azanickelacycle 37. Subsequent alkyne insertion to the azanickelacycle and reductive elimination lead to the formation of 38. 

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