Base-Catalyzed Povarov Reaction: An Unusual [1,3] Sigmatropic Rearrangement to Dihydropyrimidobenzimidazoles

Abstract

A novel base-catalyzed Povarov reaction of arylamines, aldehydes, and electron-deficient dienophiles has been developed. An unprecedented in situ [1,3] sigmatropic rearrangement leading to 4,10-dihydropyrimido[1,2-a]benzimidazoles has also been discovered. An insight of the plausible mechanism is discussed and supported by X-ray crystal study. This cascade reaction is achieved in a one-pot multicomponent fashion on soluble support under microwave conditions.

Electrochemical Synthesis of Tetrahydroquinolines from Imines and Cyclic Ethers via Oxidation/Aza‐Diels‐Alder Cycloaddition

“…Experimental Section 1 H and 13 C NMR spectra were recorded on Bruker AVANCE II 300 spectrometer (300.13 and 75.48 MHz, respectively) in CDCl 3 . Chemical shifts were reported in parts per million (ppm), and the residual solvent peak was used as an internal reference: 1 H (CDCl 3 δ = 7.25 ppm), 13 C (CDCl 3 δ = 77.00 ppm). Multiplicity was indicated as follows: s (singlet), d (doublet), t (triplet), q (quartet), sept (septet), m (multiplet).…”

“…[1] This reaction is traditionally catalyzed by Bronsted [2] and Lewis acids [3] . Also Mn/Ag system, [4] CAN, [5] TfOH/CuI, [6] Co(III) complexes, [7] Ph 3 P ⋅ HClO 4 , [8] chiral urea catalyst, [9] Tf 2 NH/TfOH, [10] fluoroalcohols, [11] α‐chymotrypsin from bovine pancreas, [12] piperidine, [13] molecular sieves, [14] heterogeneous acidic catalysts, [15] I 2 in aqueous micelles [16] were applied as the catalyst in the Povarov reaction. Reverse regioselectivity was achieved by photocatalytic methods [17] .…”

Synthetic Strategies for Preparing Bicyclic Guanidines

“…[95] In 2003, Kundu and co-workers reported the solid-phase synthesis of BGs with structures related to that of anagrelide. In the latter approach, 2-aminobenzimidazole derivatives 170 attached to the resin were treated with aromatic aldehydes 175 and suitable dienophiles 176 to produce 6+5 BG compounds 179, based on the dihydropyrimidine-benzimidazole scaffold (Scheme 53).…”

Diversity-Oriented Synthesis of Coumarin-Linked Benzimidazoles via a One-Pot, Three-Step, Intramolecular Knoevenagel Cyclization

“…DAO inhibitors help to increase the d -serine levels in the serum and cerebrospinal fluid of schizophrenic patients. , In the literature, benzopyrrole ( V , IC 50 = 1.34 μM) and benzoxazole ( VI , IC 50 = 1.88 μM) derivatives were found as the human DAO inhibitors. In continuation of our interest to synthesize biologically important heterocycles, , we wish to report herein an efficient method for the synthesis of coumarin linked benzimidazoles under mild conditions and their evaluation of initial pk DAO activity.…”