2-Alkoxycarbonylpyridinium N-Aminides: 1,3-Dipoles or 1,4-Nucleophile−Electrophile Synthons? Experimental and Theoretical Evidence for the Mechanism of Pyrido[1,2-b]pyridazinium Inner Salt Formation
摘要:
2-Alkoxycarbonylpyridinium N-aminides behave as 1,3-dipoles toward acetylenic compounds and as 1,4-nucleophile-electrophiles with heterocumulenes in a [4 + 2] cyclocondensation process, yielding in the latter case conjugated mesomeric betaines. These N-aminides also behave as 1,3-dipoles when reacted with olefinic dipolarophiles, producing the corresponding cycloadducts that, depending on their regioisomeric nature, subsequently undergo a ring expansion process to produce pyrido[1,2-b]-pyridazinium inner salts. A mechanistic investigation performed using both PM3 frontier molecular orbital (FMO) and potential energy surface (PES) analysis at the RHF/6-31+G* level indicates that both the cycloaddition reaction and the ring expansion occur in a concerted way rather than through a stepwise mechanism via a zwitterionic intermediate.
Herein, we report a regioselectivecycloaddition strategy of N-aminopyridinium ylides with electron-deficient alkenes, in the presence of a hypervalent iodine reagent, PhI(OAc)2. A variety of multifunctionalized pyrazolo[1,5-a]pyridine architectures were smoothly afforded by the reactions of pyridine-, quinoline-, and isoquinoline-based N-ylides with diverse alkenes with or without a halogen atom adjacent
在此,我们报告了在高价碘试剂 PhI(OAc) 2存在下,N -氨基吡啶鎓叶立德与缺电子烯烃的区域选择性环加成策略。通过吡啶基、喹啉基和异喹啉基N-叶立德与具有或不具有与吸电子基团相邻的卤素原子的多种烯烃的反应,顺利地得到了各种多功能化的吡唑并[1,5- a ]吡啶结构(EWG)在宽松的条件下。
Tominaga, Yoshinori; Ichihara, Yuichi; Mori, Tomoko, Journal of Heterocyclic Chemistry, 1990, vol. 27, # 2, p. 263 - 268