Synthesis of Amidines and Benzoxazoles from Activated Nitriles with Ni(0) Catalysts

Abstract

Amidines and 2-substituted benzoxazoles were synthesized from N-heterocyclic nitriles under mild conditions (50 °C, 48 h, two steps) in an atom-economical process that involves addition of methanol, the solvent, to a nitrile moiety to yield a methyl imidate and the subsequent extrusion of solvent in the presence of amines to afford the title compounds. Methyl imidate formation was achieved by developing a new catalytic pathway using [(dippe)­Ni­(H)]2 (dippe = 1,2-bis­(diisopropylphosphino)­ethane), [Ni­(cod)2]/dppe, or [Ni­(cod)2]/P­(OPh)3 (cod = 1,5-cyclooctadiene, dppe = 1,2-bis­(diphenylphosphino)­ethane, P­(OPh)3 = triphenyl phosphite) as the catalyst precursor. Regarding the ligands, for a given substrate, namely 4-cyanopyridine, the best performance for the Ni(0)-catalyzed system was found for the σ-donor bidentate dippe, whereas the monodentate π acceptor P­(OPh)3 was less efficient. In relation to the substrates, for a given Ni–dippe system, steric hindrance and, more importantly, substrate electron-withdrawing character control imidate formation and thus the yield of amidines and benzoxazoles.

Methanolysis of 2-Cyanopyridine in the Coordination Sphere of Manganese(II). The Structure of Mn4L6Cl2 cluster (L = Methyl Picolinimidate)

“…The methanolysis of the initial 2cyanopyridine takes place upon coordination with the Mn(II) ion as a chelating bidentate ligand through the two nitrogen atoms of the pyridine ring and the carbonitrile group. As observed previously, the coordination of 2-cyanopyridine to some divalent metal ions activates the CN triple bond and makes it much more amenable toward nucleophilic attack by CH3OH molecules [12,13]. The proposed stoichiometry for complex 1, Mn4L 2 6Cl2, in which six O-methyl picolinimidate ligands are in a monoanionic mode (L 2 ) − , was confirmed by analytical and spectroscopic data.…”

Efficient Copper-Catalyzed Multicomponent Synthesis of N-Acyl Amidines via Acyl Nitrenes

“…Multiple methods exist for the synthesis of amidines in general, including the Pinner reaction, 13 substitution of phenoxyimidates, 14 Beckman-type rearrangements, 15 and dehydrogenative coupling reactions, 16,17 or by catalysis with palladium 14,18−21 or nickel, 22 as well as some multicomponent reactions. 23−33 Chang developed strategies for the synthesis of sulfonated and phosphorylated amidines via traditional click chemistry with azides, followed by a thermal N 2 exclusion, resulting in a net coupling of a nitrene to an alkyne.…”

Modeling the OEC with Two New Biomimetic Models: Preparations, Structural Characterization, and Water Photolysis Studies of a Ba–Mn Box Type Complex and a Mn4N6 Planar-Diamond Cluster

“…The methanolysis of the initial 2-cyanopyridine takes place upon coordination with the Mn(II) ion as a chelating bidentate ligand through the two nitrogen atoms of the pyridine ring and the carbonitrile group. As observed previously, the coordination of 2-cyanopyridine to some divalent metal ions activates the CN triple bond and makes it much more amenable toward nucleophilic attack by CH 3 OH molecules [32][33][34] Figure S2). The IR spectrum for 2 also confirms the methanolysis reaction of the 2-cyanopyridine to give the O-methyl picolinimidate ligand.…”