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.
Balaban
Alexandru T
AT
Texas A&M University at Galveston, 5007 Avenue U, Galveston, Texas 77551, USA. balabana@tamug.edu
Ghiviriga
Ion
I
Czerwinski
Edmund W
EW
De
Priyadarsi
P
Faust
Rudolf
R