Azanickelacyclic intermediates

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... 

Meanwhile, Miura et ah, independently, synthesized a five-membered azanick-elacycle 26 via an effective reaction sequence involving oxidative addition of 1,2,3-benzotriazin-4(3i/)-ones 25 to a low-valent nickel and elimination of dinitrogen (Scheme 12.10) [13]. The reaction affords diversely substituted isoquinolones 27 and proceeds even at ambient temperature. Subsequently, Yamauchi et al. carried out isolation and x-ray single-crystal analysis of a five-membered azanickelacycle intermediate, which is an analog of 26, by the stoichiometric reaction of benzotriazin-4(3//)-one and Ni(0) [14]. 

Nickel-catalyzed [4 + 2] cycloaddition using C—H bond activation was also developed by Nakao et al. (Scheme 12.27) [31], Formamide 66 reacted with 4-octyne in the presence of nickel catalyst gave substituted dihydropyridone 67 in good yield. Shiota et al. reported that chelation-assisted C—H bond activation enables [4 + 2] cycloaddition of amide 68 with alkynes to provide isoquinolone (Scheme 12.28) [32]. The key azanickelacycle intermediate 69 was generated in situ via N—H bond and C—H bond activation with chelation assistance by a 2-pyridinylmethylamine moiety. 

An interesting oxidatively induced reductive elimination of azanickelacycles, such as 40 and 57, proceeds with l,r-diacetylferro-cenium tetrafluoroborate, which suggests that the reaction proceeds through a Ni(III) intermediate (Scheme 21). ... 

The Rh(I)/dppf complex-catalysed 2-i-2-i-2-cycloaddition of oximes and diynes formed substituted pyridines in moderate to good yields (88%), under mild conditions. A one-pot procedure has been developed using aldehydes.The Ni-catalysed 2 -I-2 -I-2-cycloaddition of isocyanates (117) with 1,3-dienes (118) in MeCN produced 6-substituted dihydropyrimidine 2,4-diones (119). A key intermediate in this reaction is a five-membered azanickelacyclic species (Scheme 35). " The enantioselective cationic Rh(I)-catalysed 2-i-2-i-2-cycloaddition of diynes and isocyanates formed axially chiral pyridones with high ees (82%). The unique source of chirality is provided by a system containing [Rh(cod)Cl]2, l,4-bis(diphenylphosphino)butane, and the silver phosphate salt Ag(5)-TRIP. " " The Rh-catalysed 2-I-2-I-2-cycloaddition of diynes to sulfonimines in DCE, at r.t. to 80 °C, yielded 1,2-dihydropyridines in good yields (54-86%) and enantioselectivity (61-96%... 

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... 

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