1,4‐Diazabicyclo[2.2.2]octane (DABCO) as an Efficient Reagent for the Synthesis of Isoxazole Derivatives from Primary Nitro Compounds and Dipolarophiles: The Role of the Base

Abstract

The dehydration of primary nitro compounds can be performed by bases in the presence of dipolarophiles. The reactivity of several tertiary amines or azaheteroaromatic compounds containing one or two basic centres is shown to be related to the ability of the protonated base to establish Hbonded ion pairs with the adduct that is formed from the nitronate and the dipolarophile in chloroform. Among the organic bases examined, caged tertiary diamine 1,4-diazabicyclo[2.2.2]octane (DABCO) gave the best results. The reaction

Synthesis of 4,5‐Dihydroisoxazoles by Condensation of Primary Nitro Compounds with Alkenes by Using a Copper/Base Catalytic System

“…[25] We have recently reported a convenient procedure for the condensation of primary nitro compounds with alkynes (to isoxazoles) or alkenes (to isoxazolines) under base catalysis. [26][27][28][29] This method avoids the use of a dehydrating agent, but requires a catalytic amount of a suitable organic base instead, such as 1,4-diazabicycloA C H T U N G T R E N N U N G [2.2.2]octane (DABCO) or 1-methylimidazole. This process appears to occur without the formation of intermediate nitrile oxides and it can be regarded as a condensation process [Eq.…”

Acid–Base‐Catalysed Condensation Reaction in Water: Isoxazolines and Isoxazoles from Nitroacetates and Dipolarophiles

“…[42] The conversion enhancement caused by both base and water is dramatic for the "in water" reaction of allyl al- cohol (Table 2, entry 10) and occurs even at a lower temperature ( Table 2, entry 11). The base specificity observed in chlorofom [27] is lost in reactions carried out either "in water" or "on water". The results of the reactions are scarcely affected irrespective of whether DABCO, pyridine, triethyl-A C H T U N G T R E N N U N G amine, sodium hydroxide, or sodium carbonate are used (0.1 equiv with respect to dipolarophile: Table 2, entries 10-18).…”

“…Reaction in water/reaction on water: As reported in our previous papers, [27,28] ethyl nitroacetate reacts with various dipolarophiles under base catalysis to afford 3-ethoxycarbonylisoxazolines by a cycloaddition-condensation reaction process. To date, these reactions have been conveniently and successfully carried out in chloroform.…”

“…(2)]. [26][27][28][29][30][31] Whereas the former method requires anhydrous conditions and dehydrating reagents in stoichiometric amounts, [32,33] the latter condensation reaction in chloroform relies on the acid-catalysed deAbstract: Base-catalysed condensation reactions of nitroacetic esters with dipolarophiles to give isoxazole derivatives proceed faster, and often with higher yields, in the presence of water than in organic solvents such as chloroform. Kinetic profiles show that induction times are greatly reduced when the reaction is performed "in water" or "on water".…”

A facile one-pot synthesis of novel 1-substituted 2-(8-hydroxyquinolin-5-yl)-1,5,6,7-tetrahydro-6,6-dimethyl- 4H-indol-4-one derivatives

“…12 In recent years, 1,4-diazabicyclo[2.2.2]octane (DABCO) has emerged as a promoter for various organic reactions. [13][14][15][16][17] DABCO is an organic base that can act as a nucleophile. In view of this, and as part of our work on multi-component reactions, [18][19][20][21][22] we here report a simple, practical, and generally three-component reaction for the synthesis of novel indole derivatives by one-pot three-component reaction of 5-chloroacetyl-8-hydroxyquinoline, alkyl-, aryl-and heteroaryl-amines, and dimedone; the reaction is catalyzed by DABCO.…”