Simple Synthesis of a Weak Nucleophilic Base (4-Ethyl-2,6-diisopropyl-3,5-dimethylpyridine) Evidencing a Double Janus Group Effect

By analogy with 2,6-di-tert-butylpyridine and its 4-methyl-substituted derivatives, which are
nonnucleophilic bases, 4-ethyl-2,6-diisopropyl-3,5-dimethylpyridine (4) is also such a base. The
isopropyl groups (Janus-like groups) are forced by the neighboring methyl groups to turn their
“tert-butyl-analogue face” toward the heteroatom, thereby protecting it sterically against electrophilic
attack. The synthesis proceeds in two stages via the corresponding pyrylium salt 3 that is obtained
by alkene diacylation. X-ray data for 4, its picrate, and the hexafluorophosphate of 3 confirm that
the ground-state conformation agrees with the Janus effect prediction. The chemical behavior of 4
indicates that it is indeed a weak nucleophilic base, which is able to substitute the nonnucleophilic
bases in organic syntheses. The compound 3 reacts at normal pressure with methylamine or
ethylamine, forming N-alkylpyridinium salts. The cationic polymerization of isobutene in the
presence of 4 was also investigated.