Alkylpyridines metalation

The amide ions are powerful bases and may be used (i) to dehydrohalogenate halo-compounds to alkenes and alkynes, and (ii) to generate reactive anions from terminal acetylenes, and compounds having reactive a-hydrogens (e.g. carbonyl compounds, nitriles, 2-alkylpyridines, etc.) these anions may then be used in a variety of synthetic procedures, e.g. alkylations, reactions with carbonyl components, etc. A further use of the metal amides in liquid ammonia is the formation of other important bases such as sodium triphenylmethide (from sodamide and triphenylmethane). 

The gas phase acid-catalyzed synthesis of pyridines from formaldehyde, ammonia and an alkanal is a complex reaction sequence, comprising at least two aldol condensations, an imine formation, a cyclization and a dehydrogenation (9). With acetaldehyde as the alkanal, a mixture of pyridine and picolines (methylpyridines) is formed. In comparison with amorphous catalysts, zeolites display superior performance, particularly those with MFI or BEA topology. Because formation of higher alkylpyridines is impeded in the shape-selective environment, the lifetime of zeolites is much improved in comparison with that of amorphous materials. Moreover, the catalytic performance can be enhanced by doping the structure with metals such as Pb, Co or Tl, which assist in the dehydrogenation. 

Alkylpyridines. The reaction between ethylene and 3-alkylpyridines in the presence of alkali metal is much more complicated than similar reactions made with the corresponding 2 and 4 isomers (29). The two primary products from the reaction of 3 -ethylpyridine with ethylene in the presence of either sodium or potassium are 3-sec-butylpyridine and cyclic compound M. Further ethylation occurs with a longer reaction time to form 29. 

Finally, pyridine derivatives can be reduced by metals. Piperidine is obtained from pyridine with sodium in alcohols Ladenburg reaction) piperidines, as well as tetrahydropyridines, are obtained from 4-alkylpyridines. A -Alkylpyridinium ions are converted into 7V-alkylpiperidines by metals such as Zn or Sn in an acidic medium, or by electrochemical reduction (122 - 125, see p 293). 

The enaminate anions produced by deprotonating a- and 7-alkylpyridines can participate in a wide range of reactions, " being closely analogous to enolate anions. Similar side-chain carbanion formation is seen in ortho- but not me/a-nitrotoluene. Side-chain metallation of 2-/-butylcarbonylamino-4-methylpyridine proceeds at room temperature. ... 

Metal acetylacetonate mixed-ligand complexes of pyridine or alkylpyridine... 

Metal Ion Catalysis.—Mercury(u). The most commonly encountered catalyst for aquation of cobalt(m) complexes is mercury(n). In aquation of a series of complexes c y-[Co(en)2LCl] +, where L = an alkylpyridine, the mechanism proposed is a rapidly established pre-equilibrium... 

Similar examples of regioselective metalation of 3-alkylpyridine-BF3 complexes with the use of TMP-zincate were reported by Michl and co-workers in 2002 [70]. The reaction occurred at the less hindered one of the two reactive positions, as evidenced by trapping of the pyridyl zincates with iodine to afford the 2-iodo-5-alkyl pyridine derivatives in good yields (Eq. 19). 

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