L,8-Diazabicyclo

The physical properties of polyurethane adhesives result from a special form of phase separation which occurs in the cross-linked polyurethane stmcture. The urethane portions of polyurethanes tend to separate from the polyol portion of the resin, providing good shear strength, good low temperature flexibiUty, and high peel strength. Catalysts such as dibutyltin dilaurate [77-58-7], stannous octoate [1912-83-0], l,4-diazabicyclo[2.2.2]octane... 

Conditions cited for Rh on alumina hydrogenation of MDA are much less severe, 117 °C and 760 kPA (110 psi) (26). With 550 kPa (80 psi) ammonia partial pressure present ia the hydrogenation of twice-distilled MDA employing 2-propanol solvent at 121°C and 1.3 MPa (190 psi) total pressure, the supported Rh catalyst could be extensively reused (27). Medium pressure (3.9 MPa = 566 psi) and temperature (80°C) hydrogenation usiag iridium yields low trans trans isomer MDCHA (28). Improved selectivity to aUcychc diamine from MDA has been claimed (29) for alumina-supported iridium and rhodium by iatroduciag the tertiary amines l,4-diazabicyclo[2.2.2]octane [280-57-9] and quiaucHdine [100-76-5]. 

B. Di-tert-butyl dicarbonate. A solution of 20.0 g. (0.076 mole) of di-i-butyl tricarbonate in 75 ml. of carbon tetrachloride is placed in a 600-ml. beaker fitted with a magnetic stirrer, and 0.10 g. (0.0009 mole) of freshly sublimed l,4-diazabicyclo[2.2.2]octane (DABCO) is added (Note 9). Rapid evolution of carbon dioxide begins at once. The reaction mixture is stirred at 25° for 45 minutes to complete the loss of carbon dioxide (Note 10), and then 35 ml. of water, containing sufficient citric acid to make the aqueous layer slightly acidic, is added. The layers are separated and the organic layer is dried over anhydrous magnesium sulfate and then concentrated at 25° with a rotary evaporator. The residual liquid is distilled under reduced pressure to separate 13.3-15.1 g. (80-91%) of di-butyl dicarbonate as a colorless liquid, b.p. 55-56° (0.15 mm.) or 62-65° (0.4 mm.) n T> 1.4071-1.4072 (Note 11). 

The submitters report that both l,4-diazabicyclo[2.2.2]octane and triethylamine have been used to catalyze this decomposition. Tri-ethylamine was less satisfactory as a catalyst because of its relatively rapid reaction with the solvent, carbon tetrachloride, to form triethylamine hydrochloride and because of difficulty encountered in separating triethylamine from the dicarbonate pi oduct. The 1,4-diazabicyclo-[2.2.2]octane was efficiently separated from the dicarbonate product by the procedure described in which the crude product was washed with very dilute aqueous acid. 

By structural complementarity, dicationic l,4-diazabicyclo[2.2.2]octane (VII) provides an appropriate recognition site for phosphate ions and two stearyl side chains attached to the amines add lipophilic properties 59,60). Such a carrier model can selectively extract nucleotides from aqueous solution to chloroform solution via lipophilic salt formation. The order of nucleotide affinity is ATP > ADP > AMP. The selectivity ratios were 45 for ADP/AMP and 7500 for ATP/AMP at pH 3. The relative transport rate was ATP > ADP > AMP. The ratios were 60 for ATP/AMP and 51 for ADP/AMP. The modes of interaction of ADP and ATP are proposed to be as shown in Fig. 6. 

Treatment of the Z-aldehyde 9 (R1 = R2 = H) with trifluoroacetic acid in dichloromethane at — 10 C, then with l,4-diazabicyclo[2.2.2]octane or /V,/V-diethylpyridin-4-amine, constitutes the first synthesis of 27/-azepine (10, R1 = R2 = H) which was isolated, with great difficulty and in very low yield (1 %), as a highly volatile, unstable oil, the structure of which was confirmed by high field H and 13CNMR spectroscopy.290 Similar treatment of the Z-alkenones 9a-d furnishes the thermally unstable (5)-2/7-azepines lOa-d in much higher yields.291... 

In a study of the photoreduction of zinc(II) or magnesium chlorophyll derivatives 8 with ascorbic acid in the presence of l,4-diazabicyclo[2.2.2]octane (DABC-O), a 2,3-m-hydrogenated isobacteriochlorin 9 is formed which subsequently rearranges to a 3-ethylidenc derivative... 

The easiest access to most benzyllithium, -sodium, or -potassium derivatives consists of the deprotonation of the corresponding carbon acids. Hydrocarbons, such as toluene, exhibit a remarkably low kinetic acidity. Excess toluene (without further solvent) is converted into benzyllithium by the action of butyllithium in the presence of complexing diamines such as A. Af.Af.jV -tetramethylethylenediamine (TMEDA) or l,4-diazabicyclo[2.2.2]octane (DABCO) at elevated temperatures1 a procedure is published in reference 2. 

Triethylene diamine (TEDA also known as l,4-diazabicyclo[2.2.2]octane, or DABCO) is a powerful catalyst with a high selectivity for gellation. One reason... 

In the presence of a base such as l,4-diazabicyclo[2.2.2]octane (DABCO) or tri-alkylphosphines, conjugated carbonyl compounds such as esters and amides add to aldehydes via the a-carbon to give a-alkenyl-P-hydroxy esters or amides. This sequence is called the Baylis-Hillman reaction and a simple example is... 

A practical and efficient set of conditions were developed using a stoichiometric base catalyst, l,4-diazabicyclo[2,2,2]octane (DABCO)... 

The high selectivity that the system shows to pyrazine 20 compared to the stronger base pyridine, indicates that the diamine is chelated between the carboxylic acid functions as in 21. Spectroscopic evidence in the form of upfield shifts in the NMR spectra of the complexes supports such structures. Not only aromatic diamines are accommodated but also aliphatics such as l,4-diazabicyclo[2.2.2]octane (DABCO) in complex 22. Typically, exchange rates into and out of these complexes are such that they appear fast on the NMR time scale at ambient temperature, but exchange can be frozen out at low temperatures20. For DABCO, an activation barrier of 10.5 kcal M 1 was observed at Tc = 208 °K. 

Diethylzinc forms a colorless monoadduct with l,4-diazabicyclo[2,2,2]octane (dabco) 34 and an orange-colored bis-adduct with acridine.79 The mono-dabco adduct, Figure 14, crystallizes in the form of infinite zigzag chains, in which each diethylzinc moiety bridges two dabco units. The coordination environment about zinc is distorted tetrahedral, with Zn-C and Zn-N bonds ranging from 1.93(3) to 2.10(2) A and from 2.24(2) to 2.37(2) A, respectively. 

Alkyl 2-(hydroxymethyl)acrylates are versatile functionalized monomers and synthetic building blocks. Conventional preparations employ the Baylis-Hillman reaction which involves the addition of formaldehyde to the parent acrylate ester, catalyzed by l,4-diazabicyclo[2.2.2]octane (DABCO). These reactions typically take several days at room temperature, but can be achieved within minutes in the CMR and MBR (Scheme 2.4). Rapid heating under pressure prevents loss of formaldehyde. Subsequent cooling limits hydrolysis of the product, as well as dimerization and polymerization [33],... 

Spectroscopic and kinetic investigations of the reactions between 4,6-dinitrobenzofuroxan, 4-nitrobenzofuroxan, and tertiary and secondary amines (i.e., l,4-diazabicyclo[2.2.2]octane, quinuclidine, l,8-diazabicyclo[5.4.0]undec-7-ene, and piperidine) indicate the formation of zwitterionic or anionic complexes (Equation 2). The equilibrium between zwitterionic and anionic complexes is discussed (for reaction with piperidine) on the basis of H NMR spectral data, which indicate the presence of anionic complexes arising from the zwitterionic complex by a fast proton departure. The stability and the rate of formation of title complexes are discussed and compared to similar reactions of 1,3,5-trinitrobenzene <2001J(P2)1408>. 

The side products of the reaction between benzoylnitromethane 279 and dipolarophiles (norbornene, styrene, and phenylacetylene) in the presence of l,4-diazabicyclo[2.2.2]octane (DABCO) were identified as furazan derivatives (Scheme 72). The evidence reported indicates that benzoylnitromethane gives the dibenzoylfuroxan as a key intermediate, which is the dimerization product of the nitrile oxide. The furoxan then undergoes addition to the dipolarophile, hydrolysis, and ring rearrangement to the final products (furazans and benzoic acid) <2006EJ03016>. 

Oxaziridines, 6-oxa-l,4-diazabicyclo[3.1.0]hex-3-enes (245) and their 4-oxides (246), obtained in the photolysis of 4H -imidazole-3-oxides (223) and 1,3-dioxides (219), underwent a quick thermal isomerization to the starting nitrones. Further... 

RhCl(PPh3)3 is an effective catalyst for the deprotection of allyl ethers in the presence of l,4-diazabicyclo[2.2.2]oc-tane (DABCO) (Equation (20)).74 75 The role of the base is to prevent hydrolysis of prop-l-enyl ether to propanal, which poisons the catalyst. 

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