1.4- diazabicyclo -octane DABCO

Separation of relatively pure para-cresol from mixed cresols using an organic solvent and thereafter formation of a solid crystalline complex with the solvent has been reported. Piperazine and DABCO (diazabicyclo-octane) have been found to be very effective as extracting agents in this process of separation. There is very little effect of m-cresol in this process. The values of separation factor approach infinity as 100% p-cresol-base complex is crystallized. The yield of p-cresol was impressive with some aliphatic polar solvents, but... 

Historically, the most effective N-based organic catalysts were nucleophilic unhindered tertiary amines such as DABCO (diazabicyclo[2.2.2]octane, 1) [23], qui-nuclidine (2), 3-hydroxy quinuclidine (3-HDQ, 3), 3-quinuclidone (4) and indoli-zine (5) (Fig. 5.1) [24]. A direct correlation has been found between pKa and the activity of the quinuclidine-based catalysts the higher the pKa, the faster the rate [25]. More recently, l,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 6), considered as a hindered and non-nucleophilic base, was shown to be a better catalyst than DABCO, or 3-HDQ [26]. The reason for the increased reactivity for this catalyst was attributed to stabilization of the zwitterionic enolate by delocalization of the positive charge. Other N-based catalysts such as N,N-(dimethylamino)pyridine... 

For the synthesis of 18 trichlorophosphine is alkylated to dichloro[bis(tri-methylsilyl)methyl]phosphine by means of the appropriate Grignard reagent. The subsequent elimination of HC1 can be achieved with, for example, diazabicyclo-octane (DABCO), however, the use of triethylamine is advantageous for the work-up.37,38... 

Hydroxy>3-meihyleneirldecan-2-one (2). A solution ol decanal 1 (3.12 g. 20 mmol), methyl vinyl ketone 2 (1.4 g, 20 mmol) and 1.4-diazabicyclo-octane (DABCO) (0 33 g. 

Zeolite Beta is normally prepared at high alkaline pH with a templating mixture of Et4N and Na cations which in addition are not specific for this structure [72]. This synthesis can also be carried out in F" medium H = 7-10) with diazabicyclo-octane (DABCO) [73]. While with OH" anions the size of the crystals is generally below about 0.5 pm, in the presence of F" anions and without alkali cations, crystals have a pseudo octahedral morphology with a size up to 10 im(Figure 33.). 

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). 

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 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. 

Diarylhydrazines, from ArNJ 195 Diarylmercury compounds 273 f. 1,4-Diazabicyclo [2.2.2]octane (DABCO) 360 Diazenes 6, 126, 192, 195, 211, see also Azo compounds... 

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. 

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