DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) - A nucleophillic base

(A) The Baylis-Hillman reaction is of great synthetic utility, as it converts simple starting materials into densely functionalized products. Recently, Agarwal et al. showed the superiority of DBU over other amine catalysts in the Baylis-Hillman reaction, as it was stable under the reaction conditions and gave a clean reaction with the fastest rate.9 (B) The conversion of primary or secondary nitroalkanes into aldehydes or ketones, i.e. Nef reaction originally involved strong acidic conditions. Ballini et al. showed an unprecedented behavior of DBU as a new reagent in acetonitrile solution for the one-step regio- and chemoselective conversion of secondary nitro compounds in the presence of primary nitro compounds into ketones under homogeneous basic conditions in good yields.10 (C) Mizuno et al. developed a new chemical fixation of carbon dioxide in the presence of DBU to form substituted 1H-quinazoline-2,4-diones, which are useful for the synthesis of different medicinal intermediates. In this reaction, CO2 smoothly reacts with 2-aminobenzonitrile under mild conditions, assisted either by an excess of DBU (1 atm, 20°C) or catalytic amount of DBU (10 atm, 80°C) to give the corresponding quinazoline derivatives.11 The authors also synthesized substituted 2,4-dihydroxyquinazolines by chemical fixation of CO2 (1 atm) of 2-aminobenzonitrile at 20°C in presence of DBU.12 (D) Recently, Shieh et al. showed the efficiency of DBU as a nucleophilic catalyst in the environmentally friendly method for the methylation13 and benzylation14 of N-, O- and S-atoms with non-toxic dimethylcarbonate (DMC) and dibenzylcarbonate (DBC), respectively. These authors also showed the superiority of DBU over the commonly used acylation catalyst 4-(dimethylamino)pyridine in the esterification of benzoic acid with DMC.15 (E) DBU was also found to smoothly cleave the N-acetyl and N-benzoyl derivatives of carbazoles, indoles, and nitroanilines in refluxing methanol, and the parent amines were recovered in excellent yields. The cleavage was also accomplished in acetonitrile solution under reflux and under microwave irradiation.6d (F) Recently, in the synthesis of duocarmycin and CC-1065 analogues, the parent members of an important class of potent antitumor antibiotics, Boger and his co-workers used DBU in anhydrous acetonitrile solution to bring about spirocyclization to create a cyclopropane ring in the final step of the synthesis in good yield.16.