DABCO reagents

Reagents i EtiN CN. DABCO, MeCN li Dowex 50(H ), H2O. MeOH... 

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... 

A-Halogeno-amides are familiar and convenient sources of positive halogen for the organic chemist, and the 2 1 complex formed in benzene between diazabicyclooctane (DABCO) and /V-bromsuccinimide (NBS) [48] (the numbers are the observed interatomic distances in angstroms) in effect shows one such reagent in action (Crowston et al., 1984). The N-Br-N angle is close to linear [175.1(2) A], and the bromine is poised almost midway between the two nitrogen atoms, which are of similar basicity. The... 

Oxidation of a snlfide to sulfoxide is known to be an electrophilic reaction, in contrast with nncleophUic oxidation of sulfoxide to sulfone. Since 2-nitrobenzenesulfinyl chloride/KOi oxidizes sulfides to sulfoxides selectively, intermediate 48 must be the actual active intermediate. Moreover, in the presence of l,4-diazabicyclo[2.2.2.]octane (DABCO), which is a radical capturing reagent, the oxidation of methyl phenyl sulfide to the sulfoxide was inhibited. In order to further detect the intermediate 48, pure 5,5-dimethyl-l-pyrroUne-l-oxide (DMPO) was used as a trapping reagent and spin adduct was obtained. The ESR spectrum of the DMPO spin adduct was obtained by the reaction of 02 with 2-nitrobenzenesulfinyl chloride (hyperfine coupling constants, aH = 10.0 G and aN = 12.8 G). 

The reaction can be performed in diethyl ether in the presence of iron(III) acetylaceto-nate, as reported by Nagano and Hayashi in 2004, or in the presence of FeCl(salen) or iron(III) chloride/triethylamine, as described by Bedford and coworkers (Scheme 39). The latter compared several ligands (amines , phosphines ) and the best results were obtained with triethylamine, TMEDA or DABCO. In all cases, the reactions have to be performed in refluxing diethyl ether and the Grignard reagent has to be added at once Unfortunately, these reaction conditions are only useable on a very small scale (1 mmol) but they cannot be used for large-scale applications. 

Around 1980, Tabushi and coworkers used the lipophilized, DABCO-derived diammonium salt 52 as a phase transfer reagent for the transport of nucleotides in three-phase experiments (H2O-CHCI3-H2O) [75]. Whereas AMP was discriminated in a high degree, for ADP and ATP the acceleration rates were quite similar. The transport rates were significantly diminished for uracil and guanine nucleotides because of the low solubility of the resulting complexes. 

Reaction of alkynyilithium reagents with epoxides. This reaction, particularly in the case of substituted epoxides, can be sluggish when conducted in THF alone. Doolittle1 has examined the effect of various cosolvents. Use of THF-HMPT (1 1) results in high yields and reasonable reaction rates at 0°. Of other additives examined, TMF.DA is equivalent to HMPT and is more effective than DABCO or ethylenediamine. Note that use of HMPT does not permit reaction of 1-dodecynyllithium with either cis- or trans-2,3-dimethyloxiranc even at 50° for 2 hours. 

We owe to Corey and Seebach [302] an efficient procedure for the generation of phenylthiomethyllithium (PhSCH2Li), opening the way for practical applications. They found that this reagent was produced in about a 97% yield through reaction of equimolar amounts of n-butyllithium, DABCO and thioanisole in THF at 0°C for 45 min. 

Selective silylation of ribonucleosides.2 Only the 5 -hydroxyl group of ribonucleo-sides is silylated by reaction with the reagent in THF in the presence of silver nitrate. On addition of pyridine to the reaction, 2, 5 -disilyl derivatives are formed in 80-90% yield. The actual reagent may be r-butyldimethylsilyl nitrate. Highly selective 3, 5 -disilylation can be achieved in the presence of several silver salts (AgN03, AgC104, and AgOAc) in the presence of either DABCO or 4-nitropyridine N-oxide. 

While THF or CH2CI2 are the most commonly used solvents, the solubility of the reagents or the catalyst may dictate the use of other solvents. Reactions are usually slow in DMF and in CH3CN when DABCO, DBU or DMAP were used as catalysts. An often-observed byproduct of the aza-MBH reaction is a bridged compound of type 97. This product is the result of a stepwise addition of 95 to 75 via the Mannich reaction, followed by an intramolecular conjugated addition (Michael addition) of the formed anion to the a,/ -unsaturated ketone, and thus due to the elevated basicity of the catalyst (Scheme 5.21) [92]. 

Reagents (i) CH2=CHC02CH3, DABCO (ii) AcCI, pyridine CH2CI2 (iii) CF3C02H, CH2CI2, 0 °C... 

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... 

Bis(trimethylsilyl) peroxide, (CH3)3SiOOSi(CH3)3, is prepared from trimethylsilyl chloride, l,4-diaza[2,2,2]bicyclooctane, and Dabco s complex with 2 mol of hydrogen peroxide [127]. It is used alone [228] or in the presence of catalysts such as pyridinium dichromate [236] trimethylsilyl trifluoromethanesulfonate, CF3S03Si(CH3)3 [228, 237] or tris-(triphenylphosphine)ruthenium dichloride, [(C6H5)3P]3RuCl2 [236]. This reagent oxidizes primary alcohols to aldehydes (in preference to the oxidation of secondary alcohols to ketones [236]), ketones to esters or lactones Baeyer-Villiger reaction) [238], and nucleoside phosphites to phosphates [228]. All these oxidations require anhydrous conditions. 

The action of buQ Uithium on thioanisole in THF generates (phenylthio)methyllithium in a low yield of 35%. - Corey and Seebach found that reaction of equimolar amounts of bu Uithium, DABCO and thioanisole in THF at 0 "C produces (phenylthio)methyllithium in ca. 97% yield. Dimethyl sulfide can be metalated with a butyllithium-TMEDA complex at room temperature (equation 1). Treatment of chloromethyl p-tolyl sulfide with magnesium produces the corresponding Grignard reagent a reaction temperature between 10 and 20 C is crucial for its efficient generation (equation 2). ... 

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