Reference of 3-Methyl-1H-pyrrole. The mechanism of aromatic electrophilic substitution of aromatic heterocycles is consistent with that of benzene. Compound: 3-Methyl-1H-pyrrole, is researched, Molecular C5H7N, CAS is 616-43-3, about β-Electrophilic Additions of Pentaammineosmium(II) η2-Pyrrole Complexes. Author is Hodges, L. Mark; Gonzalez, Javier; Koontz, Jason I.; Myers, William H.; Harman, W. Dean.
The reactivity of pyrrole complexes [Os(NH3)5(4,5-η2-L)]2+(OTf)2 (L = pyrrole and alkylated pyrroles, e.g., I, R = H, Me) is surveyed with various electrophiles. The pyrrole ligand undergoes alkylation or acylation with a wide variety of electrophiles (e.g., acids, alkyl triflates, anhydrides, aldehydes, ketones, and Michael acceptors) predominately at the β-position. Depending on reaction conditions, the resulting products are either β-substituted 1H-pyrrole or 3H-pyrrolium complexes, the latter of which resist rearomatization due to the electron-donating properties of the metal. In all cases observed, the initial addition of the electrophile occurs on the ring face anti to Os coordination. The Os(II)-4,5-η2-pyrrole complexes are each in dynamic equilibrium with a minor isomer where the metal binds across C(3) and C(4). In this form, the uncoordinated portion of the pyrrole ring resembles an azomethine ylide, which can undergo a 1,3-dipolar cycloaddition reaction with certain electrophiles. The resulting 7-azanorbornene complexes may be ring-opened with Lewis acids to generate α-substituted 2H-pyrrolium complexes. As with the 3H-pyrrolium species, the 2H-pyrrolium complexes are stabilized by metal coordination and thereby resist rearomatization. The selectivity between Michael addition and dipolar cycloaddition depends on the pyrrole, electrophile, solvent, temperature, the presence of Lewis acids, and in some cases, concentration The iminium C of both 2H- and 3H-pyrrolium tautomers is considerably less electrophilic than its organic analogs, but readily undergoes borohydride reduction to form complexes of 3- and 2-pyrrolines, resp. When pyrrole complexes are combined with alkyne Michael acceptors, the intermediate enolate can be trapped by the iminium C of the 3H-pyrrolium species in DMSO to form a metalated cyclobutene derivative, e.g., II (R1 = COMe, R2 = H; R1 = CO2Me). Decomplexation of most pyrrole and 3-pyrroline derivatives can be accomplished in good yield either by heating or by oxidation of the metal (CeIV or DDQ). Complexes of 2-pyrrolines are considerably more difficult to remove from the metal; however, quaternization or acylation of the nitrogen facilitates their decomplexation.
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Reference:
Synthesis and Crystal Structure of a Chiral C3-Symmetric Oxygen Tripodal Ligand and Its Applications to Asymmetric Catalysis,
Chiral lanthanide(III) complexes of sulphur–nitrogen–oxygen ligand derived from aminothiourea and sodium D-camphor-β-sulfonate