Organometallic compounds of group II. Part VII. Preparation of 4-alkylpyridines by reactions of some light metals with alkyl halides in pyridine
Abstract
Ether-free alkylmagnesium halides and alkyl-lithium compounds react with pyridine in the absence of the free metals to form 2-alkylpyridines; but in the presence of the free metals, 4-alkylpyridines are also formed. The reaction of an alkyl halide with the metal in situ in pyridine gives the 4-alkylpyridine essentially free from the 2-isomer. The use of alkyl chlorides and magnesium provides the best combination. Allyl chloride reacts with magnesium in pyridine to give 4-n-propylpyridine. The reactions of n-butyl chloride and magnesium in 2-picoline, 4-picoline, and collidine give a mixture of 2-n-pentylpyridine and 4-n-butyl-2-methylpyridine, 4-n-pentylpyridine, and a mixture of ‘bicollidinyls,’ respectively. It is suggested that the key step in the new 4-alkylation reaction involves abstraction of an alkylmetallic species by an intermediate derived from pyridine by electron transfer from the free metal.