DABCO reaction

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). 

In recent years there has been some substitution of TDI by MDI derivatives. One-shot polyether processes became feasible with the advent of sufficiently powerful catalysts. For many years tertiary amines had been used with both polyesters and the newer polyethers. Examples included alkyl morpholines and triethylamine. Catalysts such as triethylenediamine ( Dabco ) and 4-dimethyla-minopyridine were rather more powerful but not satisfactory on their own. In the late 1950s organo-tin catalysts such as dibutyl tin dilaurate and stannous octoate were found to be powerful catalysts for the chain extension reactions. It was found that by use of varying combinations of a tin catayst with a tertiary amine... 

Together with a shift of the proton from the a-carbon to the alkoxide oxygen, the tertiary amine is eliminated from the addition product to yield the unsaturated product 3. Early examples of the Baylis-Hillman reaction posed the problem of low conversions and slow reaction kinetics, which could not be improved with the use of simple tertiary amines. The search for catalytically active substances led to more properly adjusted, often highly specific compounds, with shorter reaction times." Suitable catalysts are, for example, the nucleophilic, sterically less hindered bases diazabicyclo[2.2.2]octane (DABCO) 6, quinuclidin-3-one 7 and quinuclidin-3-ol (3-QDL) 8. The latter compound can stabilize the zwitterionic intermediate through hydrogen bonding. ... 

The nucleophilic displacement reactions with azide, primary amines, thiols and carboxylatc salts arc reported to be highly efficient giving high (>95%) yields of the displacement product (Table 9.25). The latter two reactions are carried out in the presence of a base (DBU, DABCO). Radical-induced reduction with tin hydrides is quantitative. The displacement reaction with phenolates,61j phosphines,6M and potassium phthalimide608 gives elimination of HBr as a side reaction. 

In a similar way, diarylthiirene dioxides can be prepared by the reaction of triethylenediamine (TED) or DABCO with a,a-dichlorobenzyl sulfones at ambient temperatures100 (equation 41). 

A prepolymer is made first by charging Pluracol E2000 [1000.0 g, 1.0 eq., poly(ethylene oxide), 56 OH, BASF] to a suitable container equipped with a mechanical stirrer and a nitrogen gas inlet. Flush the container with dry nitrogen and add Desmodur W (264.0 g, 2.0 eq., 4,4 -methylene-bis(cyclohexyl isocyanate), 31.8% NCO, Bayer). While maintaining a positive N2 pressure on the reaction mixture, stir and heat at 80°C for 2 h. Cool the product to room temperature and check the NCO content (theory = 3.32 %). It might be necessary to warm the highly viscous prepolymer to take samples for titration. To a portion of this prepolymer (250.0 g, 0.2 eq.), add Dabco T-12 (0.25 g, dibutyltin dilaurate,... 

Place Arcol Polyol F-3022 (100 g, 0.1 eq., 56 OH, mixed PO/EO triol from Bayer) into a suitable container. To this add distilled water (3.3 g, 0.4125 eq.), Niax Silicone L-620 (0.5 g, a silicone surfactant from OSi Specialties), and Niax C-183 (0.12 g, an amine catalyst from OSi Specialties). Thoroughly blend this mixture without incorporating air bubbles. Then add Dabco T-9 (0.25 g, stannous octoate from Air Products) and mix again. The T-9 must be added last because it is quite water sensitive, so its exposure to the water-containing polyol blend should be kept to a minimum. To this polyol blend, quickly add Mondur TD-80 (42.6 g, 0.4868 eq., a mixture of 80% 2,4-TDI and 20% 2,6-TDI isomers from Bayer) and immediately stir at 3000 rpm for 5 s. Quickly pour the reaction mixture into a suitable container such as a 1-qt paper or plastic cup and allow the foam to free-rise. The stir blade may be wiped or brushed clean. 

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... 

The type of catalyst has a significant influence on the carbon dioxide emission. The measurements confirm the information from the literature that DABCO preferentially catalyzes reaction 2. 

It should be noted that Baylis-Hillman reaction of Garner s aldehyde with methyl acrylate and DABCO results in racemization of the stereocenter of the amino aldehyde [61]. In the case of substrate 56 such racemization is seriously hampered due to the large inversion barrier in three-membered ring compounds [62]. 

The solvent and temperature effects for the Michael addition of amidoxime 7 to DMAD were probed because the reaction itself occurs without any other catalysts. As shown in Table 6.2, the reaction gave a high ratio of 8E in strongly aprotic polar solvents such as DMF and DMSO (entry 1 and 2). 8E was also found as the major product in MeCN (entry 3), dichloromethane (entry 4), and xylenes (entry 5). To our delight, the desired 8Z was obtained as the major component in methanol (entry 6). The stereoselectivity of 8Z versus 8E was better at low temperature (entry 7). A similar result was observed when the reaction was run in THF or dichlo-roethane in the presence of a catalytic amount of DABCO (entries 9 and 10). 

The ratio of 8Z to HE is slightly better in the presence of DABCO in THF (Table 6.2 entry 9) than in pure methanol (Table 6.2 entry 7). Since the DABCO must be removed prior to the thermal rearrangement and the minimal impact on overall yield, we decided to run the Michael addition in methanol to afford a mixture of Z- and -adducts 8 in quantitative yield. The resulting solution of adducts 8 was solvent-switched to xylenes and heated at 125 °C for 2h, and at 135 °C for 4h to give a 62% assay yield of desired product 3. The reaction mixture was concentrated and hydroxypyrimidinone 3 was directly crystallized in 54% isolated yield as a white crystalline solid. 

Normally the reaction Is useful for the conversion of alkyl halides to primary amines without concomitant formation of secondary amines.29 Treatment of polymer 17 with hexamethylenetetramine in a mixture of ethanol/THF afforded an insoluble resin. Using diazabicyclooctane (DABCO), we demonstrated that the reaction could be limited to attack by a single nitrogen in a multifunctional amine, so we did not anticipate crosslinking via bis-quat salt formation. Hydrolysis of 2 with anhydrous HC1 in ethanol generated free amino groups as evidenced by a positive ninhydrin test, but quantitative hydrolysis could not be achieved and the product remained insoluble. One would have expected a simple bis-quat to hydrolyse and open the crosslinked structure. 

It should be noted that catalytic amounts of feA-arylureas and bis-arylthioureas greatly accelerated the DABCO-promoted Baylis-Hillman reaction of aromatic aldehydes with methyl acrylate in the absence of solvent. These robust organocatalysts were better mole-per-mole promoters of the reaction than either methanol or water and they were recovered in higher yields.106... 

Preparation of Reagent and Labelling Procedures. The structure of F-D [2-(2,4-diazobicyclo-2,2,2-octyl)-4-(5-aminofluoresceinyl)-6-morpholinyl 1,3,5-triazine] has been confirmed by its FAB-MS, IR, and H-NMR spectra (9). Briefly, F-D was synthesized by the treatment of fluorescamine isomer I with cyanuric chloride, then reaction with morpholine and DABCO (l,4-diazobicyclo-2,2,2-octane), as illustrated... 

Enantioselective hydrogenation of 2,3-butanedione and 3,4-hexanedione has been studied over cinchonidine - Pt/Al203 catalyst system in the presence or absence of achiral tertiary amines (quinuclidine, DABCO) using solvents such as toluene and ethanol. Kinetic results confirmed that (i) added achiral tertiary amines increase both the reaction rate and the enantioselectivity, (ii) both substrates have a strong poisoning effect, (iii) an accurate purification of the substrates is needed to get adequate kinetic data. The observed poisoning effect is attributed to the oligomers formed from diketones. 

Pt/Al2C>3-cinchona alkaloid catalyst system is widely used for enantioselective hydrogenation of different prochiral substrates, such as a-ketoesters [1-2], a,p-diketones, etc. [3-5], It has been shown that in the enantioselective hydrogenation of ethyl pyruvate (Etpy) under certain reaction conditions (low cinchonidine concentration, using toluene as a solvent) achiral tertiary amines (ATAs triethylamine, quinuclidine (Q) and DABCO) as additives increase not only the reaction rate, but the enantioselectivity [6], This observation has been explained by a virtual increase of chiral modifier concentration as a result of the shift in cinchonidine monomer - dimer equilibrium by ATAs [7],... 

Rees and co-workers have carried out extensive studies of the highly sulfurated bis[l,2]-dithiolo[l,4]thiazine ring system 469, formed by reaction of Hiinig s base 468 with S2C12 and l,4-diazabicyclo[2.2.2]octane (DABCO) (Equation 128) <1997AGE281>. 

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