Synthesis of novel synthetic intermediates from the reaction of benzimidazole and triazole carbenes with ketenimines and their application in the construction of spiro-pyrroles

Abstract

2-(2-Alkoxycarbonyl-1-arylamino-1-propenyl)benzimidazolium and 5-(2-alkoxycarbonyl-1-arylamino-1-propenyl)triazolium salts were synthesized in good yields from the reaction of benzimidazole and triazole carbenes with ketenimines. Upon treatment with a base, both salts were converted into novel 1,3-dipoles which underwent [3+2] cycloaddition reactions with electron-deficient alkynes and allenes to produce benzimidazole-spiro-pyrroles or triazole-spiro-pyrroles. This work provides novel synthons for the construction of multifunctional spiro-pyrrole derivatives that are not easy accessible by other synthetic methods and are potentially amenable to further transformations.

The thriving chemistry of ketenimines

“…To confirm the formation of the 1,3-dipolar intermediates, stable analogues 120 are prepared though the reaction between benzimidazole or triazole carbenes and the resulting ketenimines for X-ray diffraction characterization (Scheme 34). 39 The salts 120 are stable in part due to the electron donating ability of the nitrogen. Additionally, they can be deprotonated with t-BuOK and further used as precursors of the 1,3-dipolar intermediates to undergo cycloaddition reactions with propiolates or buta-2,3-dienoates.…”

Microwave Assisted Suzuki-Miyaura and Ullmann Type Homocoupling Reactions of 2- and 3-Halopyridines Using a Pd(OAc)2/Benzimidazolium Salt and Base Catalyst System

“…In this work the synthesis of the benzimidazole salts ( 1 – 4 , and I [ 53 ]) from 1-(4-bromobenzyl)-benzimidazole [ 54 ] is shown in Scheme 1 . Molecular structures of the new compounds 1 – 4 were identified by 1 H, 13 C-NMR, IR spectroscopic methods and elemental analysis.…”

“…After completion of the reaction, the % coupling products were determined based on aryl halides. 1-(4-Bromobenzyl)benzimidazole [ 54 ] and its salt numbered I [ 53 ] were prepared according to literature methods. The syntheses procedures of new salts 1 – 4 are given below.…”

Orthogonal Synthesis of Densely Functionalized Pyrroles and Thiophenes from the Reactions of Imidazo[1,5-a]pyridine Carbene-Derived Zwitterions with Electron-Deficient Alkynes

“…In 2006, we discovered that N -heterocyclic carbene-derived 2-thiocarbamoyl benzimidazolium and imidazolinium inner salts are unusual ambident 1,3-dipolar reagents . On the basis of the [3 + 2] cycloaddition reactions of novel 1,3-dipoles or dipolar intermediates readily available from the addition of N -heterocyclic carbenes to heterocumulenes such as isothiocyanates, isoselenocyanates and ketenimines, we have established and developed a powerful methodology for the construction of spiro- or fused pyrroles and thiophenes . The diverse reaction pathways are regulated by the nature of both N -heterocyclic carbenes and 1,3-dipolarophiles.…”