Effect of Pressure on the Rate of Methylation of a Buttressed Pyridine

Article abstract of DOI:10.1021/jo00264a013

3,5-Di-tert-butylpyridine (3) and 2,6-dimethyl-3,5-di-tert-butylpyridine (4) have been synthesized.Compound 3 was obtained by means of acid-catalyzed condensation of N-tert-butylmethanimine with N-(3,3-dimethylbut-1-enyl)piperidine; this reaction also furnished 3,5-di-neo-hexylpyridine (7).Compound 4 was prepared from Hantzsch's ester 8, by an application of the Schleyer method for converting ester groups into tert-butyl functions.The methylation rates of 3 and 4 in acetonitrile at 45 deg C were compared with those of pyridine and 2,6-lutidine.It was deduced that the two tert-butyl groups cause a retardation by buttressing by a factor of 57.Comparison with the known rates of 5- and 3-tert-butyl-2-methylpyridines (1 and 2, respectively) shows that the buttressing effect is minimized in the latter case by bending of the incipient N-methyl bond.The rates were also measured under pressure; the activation volumes follow the normal trend expected of directly hindered Menschutkin reactions.