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
与作为非亲核性碱的2,6-二叔丁基
吡啶及其4-甲基取代的衍
生物类似,4-乙基-2,6-
二异丙基-3,5-二
甲基吡啶(4)也是这样的碱。相邻的甲基会迫使异丙基(类Janus基团)将其“叔丁基类似物面”朝向杂原子,从而在空间上保护其免受亲电性攻击。经由相应的通过烯烃二酰基化获得的
吡啶鎓盐3,合成以两个阶段进行。用于X射线数据4,其
苦味酸盐,和
六氟磷酸盐3证实,基态构象与詹纳斯效果预测一致。的
化学行为4表明它确实是弱亲核碱基,能够取代有机合成中的非亲核碱基。化合物3在常压下与
甲胺或
乙胺反应,形成N-烷基
吡啶鎓盐。还研究了
异丁烯在4存在下的阳离子聚合。