2-Alkoxycarbonylcycloimmonium ylides, efficient 1,4-dipole equivalents in the synthesis of new conjugated betaines.
作者:Ana M. Cuadro、Jesús Valenciano、Juan J. Vaquero、José L. García Navío、Julio Alvarez-Builla
DOI:10.1016/s0040-4020(01)89900-2
日期:1993.4
Several heterocyclic mesomeric betaines containing the bicyclic systems pyridol[1,2-a]pyrazine and pyrido [2,1-f][1,2,4]triazine have been prepared by reaction of 2-alkoxycarbonyl pyridinium N-ylides with phenyl isocyanate and isothiocyanate.
2-Alkoxycarbonylpyridinium N-Aminides: 1,3-Dipoles or 1,4-Nucleophile−Electrophile Synthons? Experimental and Theoretical Evidence for the Mechanism of Pyrido[1,2-<i>b</i>]pyridazinium Inner Salt Formation
作者:Jesús Valenciano、Ana M. Cuadro、Juan J. Vaquero、Julio Alvarez-Builla、Raul Palmeiro、Obis Castaño
DOI:10.1021/jo9909655
日期:1999.12.1
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.
TSUCHIYA TAKASHI; ENKAKU MICHIKO; OKAJIMA SATOR, CHEM. AND PHARM. BULL., 1980, 28, NO 9, 2602-2608