Pyridination reaction

With pyridine, reaction takes place at the nitrogen rather than at a double bond, and an yUd [27032-01-5] is formed (57,58). Sulfides react similarly to give sulfOidenes and carbonyl cyanide (59). 

The dimethyl acetal (94) is readily prepared from the 22-aldehyde (93) by direct reaction with methanol in the presence of hydrogen chloride. Ena-mines (95) are formed without a catalyst even with the poorly reactive piperidine and morpholine.Enol acetates (96) are prepared by refluxing with acetic anhydride-sodium acetate or by exchange with isopropenyl acetate in pyridine.Reaction with acetic anhydride catalyzed by boron trifluoride-etherate or perchloric acid gives the aldehyde diacetate. 

In the formation of tert-butyl azidoformate by the addition of phosgene to alcohols followed by the addition of Na nitride or hydrazoic acid in the presence of pyridine, reaction of phosgene with the azide can cause the formation of expl carbazide (Ref 9)... 

Nitrophenyl 2, 3 -0,0-cyclic phosphites 18a-d were formed rapidly and cleanly as two diasteroisomers in the reaction of 5 -0-protected ribonucleosides 16a-d with tris(4-nitrophenyl) phosphite (17) in the presence of pyridine [reaction time less than 3 min at room temperature in DMF/pyridine (9 1 v/v) solution (monitored by 31P-NMR )]. Their sulfhydrolysis, which is also very rapid using an excess of hydrogen sulfide at room temperature, gave cyclic //-phosphonothioatcs 19a-d (Scheme 7) [22], In this reaction, the corresponding 2, 3 -0,0-cyclic... 

Values of ka and b are correlated by the Hammett equation for pyridines and for triaryl phosphines. Very large negative p values were found for pyridine reactions especially (35). Key values are highlighted in Table II. 

Oxygenation of pyridines. Reaction of the reagent with pyridine or 4-meth-ylpyridine results in a 2-acetoxypyridine in high yield. A similar reaction with 3-... 

Ring alkylation of salicylic acid, 22 4 Ring atoms, pyridine reactions at, 22 98-101... 

Dihydropyridines and their /V-alkyl derivatives undergo anodic oxidation in basic medium to the corresponding pyridines (reaction 27). The process may be complicated by the presence of other moieties for example, a nitro group may reductively condense... 

A one-step reaction leads to the formation of 4-thio- and 4-aminopyrrolo[3,4-f]pyridines. Reaction of an acetylpyru-vate with compounds containing an active methylene group, followed by cyclization leads to the formation of the bicyclic ring systems in good yields <2007T4491>. An aminomethylation reaction followed by cyclization leads to the formation of 2,3-dihydropyrrolo[3,4-f]pyridinones <2006OL5889>. 

No further research was performed in this field until three decades later, when Arcadi et al. developed a one-pot entry into functionalized pyridines. Reaction required a catalyst to dehydrogenate a dihydropyridine intermediate to pyridine. At that time, the liberated hydrogen was believed to be a consequence of aromatization [189]. 

Washing Procedures. The metal halide-pyridine reaction mixtures were washed in a sealed apparatus designed for continuous extraction in vacuo. Samples were transferred to and from the apparatus in a glove box under an atmosphere of argon. Washings were considered to be complete when the filtrate coming through the filter became colorless. 

When a sample of the niobium (V) chloride-pyridine or niobium(V) bromide-pyridine reaction mixture was dissolved in dilute acid, filtered to remove precipitated niobium oxides, and treated with concentrated sodium hydroxide solution, the same set of spectra were observed for the resulting solution as for the l-(4-pyridyl) pyridinium dihalides. The spectra before and after heating the solutions from the reaction mixtures are shown in Figure 2. Here also the peaks occurred at 432 and 365 m/x, with the 432-m, peak absent after heating. 

Samples of the niobium (V) chloride or niobium (V) bromide-pyridine reaction mixtures were hydrolyzed in concentrated hydrochloric acid. Aliquots were diluted and neutralized with sodium carbonate to a pH of approximately 8. Sodium tetraphenylborate(III) solution then was added and a precipitate of l-(4-pyridyl) pyridinium tetraphenylborate(III) was produced. The precipitate was filtered and extracted with concentrated hydrochloric acid. The ultraviolet absorption spectrum of the extract is shown in Figure 3 for comparison with the spectrum of a known sample of l-(4-pyridyl) pyridinium dichloride in dilute hydrochloric acid. 

Preparation of Dianiline Derivative of Glutaconaldehyde. A sample of the niobium(V) chloride-pyridine reaction mixture was hydrolyzed in dilute aqueous ammonia, and the solution was filtered to remove precipitated niobium (V) oxide. 

Table V Most Intense Powder Pattern Lines0 In Metal Halide-Pyridine Reaction Products...

Table VI. Infrared Absorption Bands for Pyridinium Bromide and Soluble Residue from CHCI3 Washing of NbBr5-Pyridine Reaction Product...

B) 2PiCH3 +C6H5CHO (PiCH2)2CHC6Hs Both reactions are catalyzed by piperidine reaction (B) is run in pyridine, reaction (A) in aromatic solvents such as benzene or toluene, A series of monosubstituted benzaldehydes react similarly via reaction (A) (Ref 23) as do also terephthalaldehyde (Ref 23), and isophthal-aldehyde (Ref 117), both with two moles of TNT. A similar product could not be made from phthalaldehyde (Ref 117), and only traces of HNS were obtained from TNT and 2,4,6-trinitrobenzaldehyde (Ref 31)... 

---