Dimethylformamide, as solvent

Non-Kolbe electrolysis of alicyclic p-hydroxy carboxylic acids offers interesting applications for the one-carbon ring extension of cyclic ketones (Eq. 35) [242c]. The starting compounds are easily available by Reformatsky reaction with cyclic ketones. Some examples are summarized in Table 13. Dimethylformamide as solvent and graphite as anode material appear to be optimal for this reaction. 

The synthetic route represents a classical ladder polymer synthesis a suitably substituted, open-chain precursor polymer is cyclized to a band structure in a polymer-analogous fashion. The first step here, formation of the polymeric, open-chain precursor structure, is AA-type coupling of a 2,5-dibromo-1,4-dibenzoyl-benzene derivative, by a Yamamoto-type aryl-aryl coupling. The reagent employed for dehalogenation, the nickel(0)/l,5-cyclooctadiene complex (Ni(COD)2), was used in stoichiometric amounts with co-reagents (2,2 -bipyridine and 1,5-cyclooctadiene), in dimethylacetamide or dimethylformamide as solvent. 

Studies of cathodic reduction have been few. Amusingly, attempted anodic oxidation of the furyl ketone 123 actually resulted in cathodic reduction to the dimer 124 the corresponding ester was oxidized normally, however.301 Sometimes the dimethoxydihydrofurans formed in oxidation processes are reduced in a side reaction leading to the tetrahydrofuran derivatives.302 By using dimethylformamide as solvent instead of the protic solvents used formerly, a Czech group has demonstrated that the cathodic reductions of furans can produce fairly stable anion radicals having ESR spectra which agree well with theory.3023... 

A very recent addition to the already powerful spectrum of microwave Heck chemistry has been the development of a general procedure for carrying out oxidative Heck couplings, that is, the palladium)11)-catalyzed carbon-carbon coupling of arylboronic acids with alkenes using copper(II) acetate as a reoxidant [25], In a 2003 publication (Scheme 6.6), Larhed and coworkers utilized lithium acetate as a base and the polar and aprotic N,N-dimethylformamide as solvent. The coupling... 

The substance 4,12-dibromo[2.2]paracyclophane is the key intermediate en route to several functional C2-symmetric planar-chiral 4,12-disubstituted[2.2]paracydo-phanes. Braddock and coworkers have shown that this important intermediate can be obtained by microwave-assisted isomerization of 4,16-dibromo[2.2]paracydo-phane, itself readily prepared by bromination of [2.2]paracyclophane (Scheme 6.88) [182], By performing the isomerization in N,N-dimethylformamide as solvent (microwave heating at 180 °C for 6 min), in which the pseudo-para isomer is insolu-... 

Kim and Varma have described the preparation of a range of cyclic ureas from diamines and urea [366]. In the example highlighted in Scheme 6.203, ethylenedi-amine and urea were condensed in the presence of 7.3 mol% of zinc(II) oxide in N,N-dimethylformamide as solvent at 120 °C to furnish imidazolidin-2-one in 95% isolated yield. Key to the success of this method is that the reaction needs to be performed under reduced pressure in order to remove the ammonia formed from the reaction mixture. This method was extended to a variety of diamines and amino alcohols [366]. 

For the cydative cleavage step, it turned out that aprotic conditions were definitely superior to the use of protic media. Thus, employing N,N-dimethylformamide as solvent at somewhat elevated temperatures furnished the desired compounds in high yields and excellent purities. Having established the optimized conditions, various phthalic acids and amines were employed to prepare a set of phthalimides (Scheme 7.51). However, the nature of the amine was seen to have an effect on the outcome of the reaction. Benzyl derivatives furnished somewhat lower yields, probably due to the reduced activities of these amines. Aromatic amines could not be included in the study as auto-induced ring-closure occurred during the conversion of the polymer-bound phthalic acid. 

The soluble polymer support was dissolved in dichloromethane and treated with 3 equivalents of chloroacetyl chloride for 10 min under microwave irradiation. The subsequent nucleophilic substitution utilizing 4 equivalents of various primary amines was carried out in N,N-dimethylformamide as solvent. The resulting PEG-bound amines were reacted with 3 equivalents of aryl or alkyl isothiocyanates in dichloromethane to furnish the polymer-bound urea derivatives after 5 min of micro-wave irradiation (Scheme 7.75). After each step, the intermediates were purified by simple precipitation with diethyl ether and filtration, so as to remove by-products and unreacted substrates. Finally, traceless release of the desired compounds by cyclative cleavage was achieved under mild basic conditions within 5 min of micro-wave irradiation. The 1,3-disubstituted hydantoins were obtained in varying yields but high purity. 

The electrochemical preparation of organozinc compounds obtained from the corresponding aromatic halides and with the use of a nickel complex as catalyst is only efficient in dimethylformamide as solvent. Moreover, in most cases and as described previously, the reaction requires the presence of excess 2,2 -bipyridine (five molar equivalents with respect to nickel) to achieve the transmetallation reaction leading to the organozinc compound and to avoid the formation of biaryl, Ar-Ar (equation 53). 

The following procedure is an operatively simple route for the synthesis of bromotrimethylsilane on a preparative laboratory scale from reagents that are readily accessible and inexpensive. This could be a method of choice in some laboratories despite the fact that bromotrimethylsilane is now commercially available (Petrach Systems, Aldrich, or Alpha). Moreover, the procedure also serves as a suitable method for the synthesis of azidotrimethylsilane and isocyanatotrimethylsilane, and is specially useful for the preparation of cyanotrimethylsilane. Thus a mixture of triphenylphosphine dibromide, hexamethyldisiloxane, and a catalytic amount of powdered metal zinc in 1,2-dichlorobenzene is heated under reflux to produce bromotrimethylsilane in nearly quantitative yield, which is simultaneously distilled over a suspension of the corresponding pseudohalogenoacid salt in N, /V-dimethylformamide as solvent.6... 

Certain aromatic hydrocarbons luminesce when raised to an excited electronic state by electrochemical energy. This phenomenon is called electroluminescence (eel) and is shown by some benzo[c]furans. The eel emission was examined in V,V -dimethylformamide as solvent with tetra-n-butylammonium perchlorate as electrolyte. - The emission was identical with the normal fluorescence emission. Cyclic voltammograms were measured under the same conditions as used for the eel studies slowest scan rates at which rereduction of the cation or reoxidation of the anion... 

This method is clearly expensive, and nowadays the cheaper sodium nitrite is employed with the alkyl halide in dimethyl sulphoxide or dimethylformamide as solvent.197 Although the yields are a little lower than in the silver nitrite method, a further feature is that secondary halides may be converted into secondary nitroalkanes, although even this modification fails with tertiary halides. The reaction is illustrated by the preparation of 2-nitrooctane (Expt 5.189). 

The experimental conditions for conducting the above reaction in dimethylformamide as solvent are as follows. In a 250-ml three-necked flask, equipped with a reflux condenser and a tantalum wire Hershberg-type stirrer, place 20g of o-chloronitrobenzene and 100ml of dimethylformamide (dried over anhydrous calcium sulphate). Heat the solution to reflux and add 20 g of activated copper bronze in one portion. Heat under reflux for 4 hours, add another 20 g portion of copper powder and continue refluxing for a second 4-hour period. Allow to cool, pour the reaction mixture into 2 litres of water and filter with suction. Extract the solids with three 200 ml portions of boiling ethanol alternatively, use 300 ml of ethanol in a Soxhlet apparatus. Isolate the 2,2 -dinitrobiphenyl from the alcoholic extracts as described above the yield of product, m.p. 124-125 °C, is 11.5 g (75%). 

Although the solvent effects are small, the alkene formation diminishes as predicted with increasing water content (corresponding to increased solvent polarity). The Sn2/E2 reaction of 2-phenylpropyl tosylate with sodium cyanide (in hexamethyl-phosphoric triamide and in A,A-dimethylformamide as solvents at 100 °C) gives a-methylstyrene (elimination product) and l-cyano-2-phenylpropane (substitution product) [75]. It has been found, in accordance with the predictions of the Hughes-Ingold rules, that the elimination/substitution ratio decreases as the polarity of the solvents (measured by the relative permittivity) increases [75]. Theoretical investigations of the... 

The occasional preliminary purification of products by aqueous washes usually coincides with the use of pyridine or dimethylformamide as solvent. Esters such as succinimido and benzotriazolyl are often prepared in situ, meaning that they are not isolated but subjected to aminolysis immediately after the esterification reaction.P " Slight decomposition can accompany the esterification of Boc amino acids, in particular if dichloromethane is used as solvent and the acidic EDC is used as reagent.P l Publications with a major focus on the synthesis of active esters using DCC are listed in Table 2. A list of Fmoc-Xaa-OR active esters that had been described to 1987 has been compiled.f l... 

Sammes and his group (77JCS(P1)663 78JCS(P1)1293 81JCS(P1)1909) attempted the thermal intramolecular cycloaddition of the substituted pyrimidine 507 possessing an alkyne to produce a monoterpene alkaloid ( )-actinidine (511)(Scheme 64). Upon thermolysis of the pyrimidine 507 at 200°C in a sealed tube, using dimethylformamide as solvent, intramolecular cycloaddition led to the known pyridone 509 in 87% yield by the loss of the amide bridge from intermediate 508. Conversion of the pyridone 509 into the chloropyridine followed by reductive dechlorination afforded racemic actinidine 511. 

Use of JV,N-dimethylformamide as solvent in copolymerizations avoids complications arising from aggregation which have been discussed in... 

Early workers [103] detected benzilic acid formed during the reduction of benzophenone in dimethylformamide in the presence of carbon dioxide. The carbon dioxide radical anion system is known to have E" = —2.2V (vs. SCE) [104] and will thus not be formed in preference to the ketone radical anion. Reaction occurs through trapping of aromatic carbonyl radical anions by carbon dioxide, and this has been developed into a convenient synthesis of aryllactic acids. The modern technological process uses constant current conditions. On a small scale, a divided cell with mercury cathode has been used to obtain benzilic acids from substituted benzophenones and carbon dioxide in 70-90% yields [105] and to convert 4-isopropylacetophenone to the corresponding phenyllactic acid in 85% yield [106]. On a technical scale, these reactions are best carried out in an undivided cell using a lead cathode and a sacrificial aluminum anode with dimethylformamide as solvent... 

The same result could be obtained with 2-phenyl-1-propene, which gave the 5-mercapto-substituted compound without solvent.30 The reaction has also been realized with dimethylformamide as solvent.31... 

Displacement of Cl or Br. Bunnett and Conner improved a previous procedure for the preparation of 2,4-dinitroiodobenzene from the chloro compound by using dimethylformamide as solvent in place of ethylene glycol. Sodium iodide was taken in fivefold molar excess, presumably on the ground that the reaction is reversible. 

The reaction of the reagent with 9,10-bis(chloromethyl)anthracene provides the simplest synthesis of anthracene-9,10-dicarboxaldehyde. Dimethyl sulfoxide is preferred to dimethylformamide as solvent. 

In a very useful modification, simple ketones with CH2 adjacent to the carbonyl (cyclic ketones work much better than acyclic ketones) and ortfto-iodo-arylamines react under palladium catalysis to give indoles directly. The use of dimethylformamide as solvent and DABCO as the base are crucial to the success of the route. Mechanistically, the sequence certainly proceeds through the enamine. As well as being conceptually and practically simple, this method tolerates functional groups that would be sensitive to the acid of the traditional Fischer sequence. This method can also be applied to aldehydes, thus providing a direct route to 2-unsubstituted indoles, including side-chain-protected tryptophans. ... 

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