Aminopyridines metalation

The initial study of aminopyridine metalation was carried out on 3-methoxy-5-pivaloylaminopyridine (200), readily prepared from the corresponding pyridine (Scheme 60) (81JOC3564). In this case, the combined activating effects of the two DMGs lead to metalation at the in-between site. Using optimum conditions (n-BuLi/THF/-25°C) followed by quench with a variety of electrophiles at -70°C led to products 201. Addition... 

The desymmetrisation of meso-l,2-diols has been achieved by Oriyama using enantiopure diamines including (12.103),and also atropisomeric 4-aminopyridines. Metal-based catalysts have also been used to good effect in... 

Alkali metal derivatives of 2-(trimethylsilyl)aminopyridines can be further derivatized by insertion of 1,3-dicyclohexylcarbodiimide. Functionalized guani-dinates are formed in this reaction via a 1,3-silyl shift. Scheme 170 illustrates the reaction sequence as well as the preparation of an aluminum complex of the modified ligand, which exhibits pseudo jS-diketiminate binding of the metal center, thus exemplifying the coordinative versatility of this new multi-N-donor system. ... 

Directed metallation continues to be developed as a convenient method for regiospecific substitution of pyridines. A mild and general procedure for the preparation of structurally diverse 4-alkyl-2-aminopyridines 37 involves the lithiation/alkylation of aminopyridine derivative 36 <96JOC(61)4810>. 

The 2-aminopyridine proton of 239 is sufficiently acidic to participate in the N-metallation reactions depicted in equation 44. The process yields crystals of dimeric structure (240) however, in the presence of a strongly binding ligand such as TMEDA the... 

Since the use of ammonia is not practical in transition metal catalyzed processes, the identification of its synthetic equivalents is of major importance. Benzophenone imine was found to couple with 3-bromopyridine readily under the above mentioned conditions (7.72.), The masking benzophenone was removed in transamination with hydroxylamine, which gave the desired 3-aminopyridine in 81% overall yield.92 Allylamine was also successfully employed as ammonia equivalent93... 

To see whether water could be activated and added to Jt-systems other than alkynes, the metal-catalyzed hydrolysis of nitriles was studied [20]. For this purpose novel homodimeric and heterodimeric bis(acetylacetonato)ruthenium(ii) complexes bearing the 6-diphenylphosphino-N-pivaloyl-2-aminopyridine (10a) and 3-diphenylphosphinoisoquinolone (Ila) ligands were prepared. The molecular structures of these precatalyst were studied in solution and also in the solid state and revealed some unusual hydrogen-bonding patterns, in particular for the heterodimeric system in which the acetylacetonato ligand is involved (Scheme 2.7). 

Metalation of either 4-N-pivaloyl or 4-N-f-Boc aminopyridines 269 followed by the bis electrophile, 3-chloro-l-iodopropane, furnishes the tet-rahydro-l,6-naphthyridine 270 (Scheme 80) (88TL5725). Application of this reaction to the corresponding 2-aminopyridines gives access to the corresponding 1,8-naphthyridine. 

Convenient syntheses of the rare thiazolo[5,4-c]pyridine 279 and 4-aminopyridine-3-thiol (281) systems have been achieved (Scheme 83) [88CI(L)302]. Thus, metalation of 263 followed by quenching with di-isopropylthiocarbonyl disulfide affords, in high yield, compound 278. Base-induced cyclization affords the thiazolopyridine 279, while treatment... 

A recent development31 is the preparation of metal polymer complexes directly on the electrode via the electrochemically induced polymerization of the metal complex. Ruthenium(II) and osmium(II) complexes with ligands containing aromatic amines, e.g. 3- or 4-aminopyridine or 5-amino-1,10-phenanthroline, are electrochemically polymerized to yield a film of the metal polymer on the electrode surface. The polymerization involves free radicals, which are formed via the initial oxidation of the metal complex to a radical cation and subsequent reaction of the radical cation with a base to yield the free radical. 

Benzeneselenenyl halides, 26 Camphor- 10-sulfonic acid, 62 Dicyclohexylcarbodiimide-4-Dimethyl-aminopyridine, 107 Hydrofluoric acid-Acetonitrile, 188 Thiophenol, 297 Lithiation (see Metallation)... 

Metal-catalysed hydrolysis of / -nitrophenyl picolinate at pH 7.5 was in the order Cu(II) > Ni(II) > Zn(II) > Co(II) > La(III). The probable mechanism is via attack by external HO- on the metal-ion complex (80).80 High catalytic activity in the hydrolysis at pH 7 of p-nitrophenyl picolinate, but not / -nitrophenyl acetate, was displayed by the metal complexes M(2-aminopyridine)2(OAc)2 (M = Zn, Ni), showing that they were good models for hydrolytic metalloenzymes.81... 

Schiff bases derived from an aminopyridine and an aromatic aldehyde find use in the spectrophotometric determination of metal ions. For example, iV,iV -bis(salicylidene)-2,3-pyridinediamine 23 has been used in the determination of copper(ll) ions. An advantage of Schiff bases derived from aminopyridines as analytical reagents lies in the simplicity of their preparative procedures <2000CCA81>. 

Figure 16 MM model of the trisaminophosphorus derivative of 2-aminopyridine (left) and its complex with a metallic atom (right)...

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