The reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with carbon dioxide

Amidines have been reported to react with CO(2) to form a stable and isolable zwitterionic adduct but previous studies were performed in the presence of at least some water. However, spectroscopy of the reaction between DBU and CO(2) detects the rapid formation of the bicarbonate salt of DBU when wet DBU is exposed to CO(2) and does not indicate that an isolable zwitterionic adduct between DBU and CO(2) forms either in the presence or the absence of water.     

An efficient Darzens reaction promoted by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)

An efficient DBU promoted Darzens reaction utilising α-haloketones containing an enolizable α′-hydrogen is reported. This method diastereoselectively afforded the corresponding α,β-epoxy ketones good to excellent yields in an one-pot reaction without using any transition metals or additives. Furthermore, haloketones without an α′-hydrogen are also applicable in this reaction.     

Unusual reaction of 1,8-diazabicyelo-[5.4.0]undec-7-ene with diethyl maleate

Michael addition of DBU on diethyl maleate and subsequent cyclization of the adduct afforded a tricyclic derivative which was susceptible to react further with a second molecule of unsaturated diester.     

Synthesis and spectrophotometric study of deprotonation of octamethylporphyrin derivatives with 1,8-diazabicyclo[5.4.0]undec-7-ene in acetonitrile

Acidic properties of synthesized 5,10,15,20-tetrakis(4′-tert-butylphenyl)-2,3,7,8,12,13,17,18-octamethylporphyrin and 5,10,15,20-tetrakis(3′,5′-di-tert-butylphenyl)-2,3,7,8,12,13,17,18-octamethylporphyrin have been studied by spectrophotometry. Deprotonation of the intracyclic nitrogen atoms with 1.8-diazabicyclo [5.4.0]undec-7-ene in acetonitrile occurs in two steps. Deprotonation constants and ranges of the porphyrinsanionic forms existence have been determined, and influence of the peripheral substituents on acidic properties of the macrocyclic ligand has been elucidated.     

Ionic liquids on the basis of 2,3,4,6,7,8,9,10-octahydropyrimido-[1,2-a]azepine (1,8-diazabicyclo[5.4.0]undec-7-ene)

New ionic liquids containing alkyl and polyfluoroalkyl substituents and various anions were synthesized from 2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepinium ion (1,8-diazabicyclo[5.4.0]undec-7-en-8-ium). Their NMR spectra and miscibility with water and organic solvents were studied.     

Thermodynamic parameters for the reaction of 1,8-diazabicyclo [5.4.0] undec-7-ene with 4-nitrophenylnitromethane in several aprotic solvents

Equilibrium constants K for reaction of the C-acid, 4-nitro/phenylnitromethane with 1,8-diazabicyclo [5.4.0] undec-7-ene have been determined in aprotic solvents over a range of temperature. Corresponding measurements have been made for the deuterated acid 4-NPNM-d₂. Thermodynamic parameters K, H^o and S^o, for proton and for deuteron transfers are not very differet in a given solvent, but show a considerable solvent dependence. There is an increase in magnitude of K with increase in solvent dielectric constant, a finding which is consistent with formation of an ion-pair. The range of extent of exothermicity of the reaction is quite small, –40 to-65 kJ-mol^–1, and the values of S^o (large, negative) indicate, in general, increasing solvent restriction by the product with increasing solvent polarity. A modest bathochromic solvatochromism of the product is observed as the dielectric constant increases.     

Reactions of 1,3-Dibromo-1,1-difluoro Compounds with 1,8-Diazabicyclo[5.4.0]undec-7-ene

Difluorodienes result from the double dehydrobromination of 4-aryl-1,3-dibromo-1,1-difluorobutanes with DBU. Attempted syntheses of analogous 4-alkyl or 4-alkoxy dienes yield monoelimination products under mild conditions and unexpected trifluoro compounds under more vigorous conditions. 4-Aryl-1,1-difluoro-1,3-butadienes react rapidly with 4-phenyl-1,2,4-triazoline-3,5-dione in Diels-Alder reactions, but these dienes are unreactive toward several other electron-deficient and electron-rich dienophiles.     

Trifluoromethanesulfonate,trifluromethylsulfonylimide, and bis(trifluoromethylsulfonyl)imide salts and ionic liquids based on 1,8-diazabicyclo[5.4.0]undec-7-ene and 1,5-diazabicyclo[ 4.3.0]non-5-ene

Trifluoromethanesulfonate, trifluoromethylsulfonylimide, and bis(trifluoromethylsulfonyl)imide salts and ionic liquids were synthesized from 2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepine (1,8-diazabicyclo[5.4.0]undec-7-ene) and 2,3,4,6,7,8-hexahydropyrrolo[1,2-a]pyrimidine (1,5-diazabicyclo[4.3.0]non-5-ene). Their physicochemical properties, spectral parameters, and some chemical transformations were studied.     

Nucleophilic catalysis with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) for the esterification of carboxylic acids with dimethyl carbonate

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) is an effective nucleophilic catalyst for carboxylic acid esterification with dimethyl carbonate (DMC). The reaction pathway of this new class of nucleophilic catalysis has been studied. A plausible, multistep mechanism is proposed, which involves an initial N-acylation of DBU with DMC to form a carbamate intermediate. Subsequent O-alkylation of the carboxylate with this intermediate generates the corresponding methyl ester in excellent yield. In the absence of DBU or in the presence of other bases, such as ammonium hydroxide or N-methylmorpholine, the same reaction affords no desired product. This method is particularly valuable for the synthesis of methyl esters that contain acid-sensitive functionality.     

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)-promoted efficient and versatile aza-Michael addition

A convenient and versatile method was developed for aza-Michael addition using a substoichiometric amount of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Various nitrogen nucleophiles were efficiently introduced to α,β-unsaturated carbonyl compounds employing 0.5 equiv of DBU. Furthermore, other heteroatomic nucleophiles could also be introduced successfully under the same reaction conditions.     

Palladium-catalysed dimerization of isoprene with carbon dioxide in the presence of organotin ethoxide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)

The palladium-catalysed dimerization of isoprene with carbon dioxide is promoted by treatment wiht tributyltin ethoxide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).     

1,8-diazabicyclo[5.4.0]undec-7-ene (dbu): An effective base for the introduction of tbutyldimethylsilyl group in organic compounds.

Reaction of alcohols, thiols, amines, carboxylic acids, phenols, hydroquinones, ketoesters and amides with equimolecular amounts of t-butyldimethylchlorosilane and DBU, even in solvents other than dimethylformamide affords the corresponding t-butyldimethylsilyl derivatives in high yield.     

Attempts to prepare aromatic O-acyl-hydroxylamines—II : Dehydrohalogenation of 1-bromo-4-acetyloxyimino-1,2,3,4-tetrahydrophenanthrene by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)

Dehydrohalogenation of 1-bromo-4-acetyloxyimino-1,2,3,4-tetrahydrophenanthrene by 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) gave a mixture of products. Thirteen of these were identified and together account for 80 per cent of the total yield. The majority are considered to be formed via the labile O-acetylhydroxylamine (17); from which it may be concluded that 17 has the following properties under the basic conditions of the reaction. (a) It may rearrange to hydroxamic acid (which gives further products). (b) It may behave as an acetylating agent. (c) Possibly it may generate a nitrenium ion. A further indication that the nitrenium ion is involved, comes from the dehydrobromination reaction when performed in the presence of α-naphthol, α-naphthylamine, 4-hydroxydiphenylamine, and hydrazobenzene. Particular attention is given to the dehydrogenating property of the nitrenium ion.     

Study of acidity and coordination properties of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin in the system of 1,8-diazabicyclo[5.4.0]undec-7-ene-acetonitrile

Spectrophotometric titration method was used to study the acidic properties of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin in the presence of a deprotonated agent, 1,8-diazabicyclo[5.4.0] undec-7-ene, in acetonitrile. The spectral characteristics of the ionized forms and combined ionization constant for the first and second stages were revealed. The reaction of complex formation between the dianionic forms of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin and zinc acetate was studied.     

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) as ligand for atom transfer radical polymerization (ATRP)

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) has been used as a bidentate ligand of copper (I) bromide for the ATRP of (meth)acrylates and styrene. With methyl methacrylate, the polymerization reached high conversions producing polymers with a good control of Mn and low polydispersity indexes (PDI = 1.19). Higher PDI were obtained with polystyrenes and poly(methyl acrylate)s. These results have been correlated to the redox properties of the catalytic complex.     

1,8-Diazabicyclo[5.4.0]undec-7-ene as a ligand in an intermediate in selective carbonyl substitution of a ruthenium-cobalt complex

1,8-Diazabicyclo[5.4.0]undec-7-ene, DBU, reacts with (OC)₄Ru(μ-PPh₂)Co(CO)₃ (1) at room temperature to give an intermediate 2, which on protonation in the presence of Co regenerates 1 and on protonation in the presence of PMe₃, gives the monosubstituted product (OC)₃(L)Ru(μ-PPh₂)Co(CO)₃ (3 L = PMe₃). DBU promotes the selective formation of 4(L = PPh₂Me) or 5 (L = Ph₂PCh₂C(Me)CH₂) in one-step from 1, Ph₂PH, and methyl iodide or methallyl chloride, respectively.     

Formation of phthalocyanines deprotonated forms and their interaction with Zn Ions in the system 1,8-diazabicyclo[5.4.0]undec-7-ene-acetonitrile at 298 K

The formation of deprotonated forms of tetra(t-butyl)phthalocyanine ((H₂ tButPc) and octa(pentoxy)-phthalocyanine (H₂OAmPc) in the system acetonitrile-1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) at 298 K was studied by the method of spectrophotometric titration. With increasing DBU concentration sequential formation occurs of both mono- and douby deprotonated forms. The introduction of pentoxy groups into the fused benzene rings leads to a significant decrease in the acidity of the tetrapyrrole macrocycle compared with the tert-butyl substitution. The interaction of douby deprotonated forms of the phthalocyanines with zinc diacetate leads to the formation of metal complexes, the chelation constant of the latter is shown to correlate with the acidity of NH-protons in the nucleus of the macrocycle. For the chelation of more acidic tetra(t-butyl)-phthalocyanine an equimolar concentrations of zinc diacetate is sufficient, while the less acidic octa(pentoxy)-phthalocyanine requires almost 6-fold excess.