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Nitroalkanes condensation

Among other reactions, the bis-metallated species (151) derived from nitroalkanes condense with dialkyl carbonates to give comp>ounds (152), in 60—80% yield, which can serve as precursors of both a-amino-acids and a-hydroxyamino-esters as well as a-keto-esters. Oxazolin-5-ones (153) can be alkylated at the 4-position by alkyl halides in hot DMF containing HMPA and ethyldi-isopropylamine. Yields are good (60—90%) for allylic, benzylic, and propargylic halides but otherwise poor (e.g. 32% with EtI) under these conditions acid hydrolysis of the products affords substituted a-amino-acids. Mesoionic l,3-oxazol-5-ones (154), obtained from imidoyl chlorides and acyl-tetracarbonylferrates, react with alcohols to give N-acyl-a-amino-acid esters. ... [Pg.130]

A combination of the techniques of the nitroalkane and the cyanohydrin reaction, using methyl cyanide, gives 2-deoxy carbohydrates containing two additional carbon atoms. The addition takes place in a manner similar to the nitroalkane condensation. A carbanion is produced by the treatment of methyl cyanide with sodium methoxide, and this adds to the aldehyde group of the carbohydrate. Two epimeric nitriles are produced that are converted into a carbohydrate by using the reactions of the Fischer-Kiliani synthesis (reaction 4.44). [Pg.97]

The above are examples of the Claisen - Schmidt reaction. The formation of p-nitrostyrenes by reaction of nitroalkanes with aromatic aldehydes in the presence of aqueous alkali may be included under the Claisen- hmidt condensation ... [Pg.709]

C From indole-3-carboxaldehvdes by condensation with nitroalkanes ... [Pg.127]

Higher nitroalkanes are prepared from lower primary nitroalkanes by a one-pot synthesis (69). Successive condensations with aldehydes and acylating agents are followed by reduction with sodium borohydride. Overall conversions in the 75—80% range are reported. [Pg.101]

A number of disinfectants apparentiy owe their activity to formaldehyde, although there is argument on whether some of them function by other mechanisms. In this category, the dmg with the longest history is hexamethylenetetramine (hexamine, urotropin) [100-97-0] which is a condensation product of formaldehyde and ammonia that breaks down by acid hydrolysis to produce formaldehyde. Hexamine was first used for urinary tract antisepsis. Other antimicrobials that are adducts of formaldehyde and amines have been made others are based on methylolate derivations of nitroalkanes. The apphcations of these compounds are widespread, including inactivation of bacterial endotoxin preservation of cosmetics, metal working fluids, and latex paint and use in spin finishes, textile impregnation, and secondary oil recovery (117). [Pg.127]

Trialkylisoxazoles have been prepared by the condensation of primary nitroalkanes under the influence of basic reagents (40JA2604). They can also be obtained from the reaction of a 1,3-diketone RCOCHRCOR with hydroxylamine hydrochloride <62HC(17)l, p. 54). [Pg.83]

Thus, various kmds of bases are effective in inducing the Henry reaction The choice of base and solvent is not crucial to carry out the Henry reaction of simple nitroalkanes v/ith aldehydes, as summarized in Table 3 1 In general, sterically hindered carbonyl or nitro compounds are less reactive not to give the desired ni tro-aldol products in good yield In such cases, self-condensation of the carbonyl compound is a serious side-reaction Several mochfied procedures for the Henry reaction have been developed... [Pg.32]

The condensation of nitro compounds and imines, the so-called aza-Henry or nitro-Mannich reaction, has recently emerged as a powerful tool for the enantioselective synthesis of 1,2-diamines through the intermediate /3-amino nitro compounds. The method is based on the addition of a nitronate ion (a-nitro carbanion), generated from nitroalkanes, to an imine. The addition of a nitronate ion to an imine is thermodynamically disfavored, so that the presence of a protic species or a Lewis acid is required, to activate the imine and/or to quench the adduct. The acidic medium is compatible with the existence of the nitronate anion, as acetic acid and nitromethane have comparable acidities. Moreover, the products are often unstable, either for the reversibility of the addition or for the possible /3-elimination of the nitro group, and the crude products are generally reduced, avoiding purification to give the desired 1,2-diamines. Hence, the nitronate ion is an equivalent of an a-amino carbanion. [Pg.16]

In practice, the condensation of nitroalkane (60) and aldehyde (59) gives nitro lactone (57) directly. Synthesis ... [Pg.270]

The generation of other heteroq cles from Bfx and Fx has been the subject of exhaustive investigation. The most important transformation of Bfx to other heterocycles has been described by Haddadin and Issidorides, and is known as the Beirut reaction . This reaction involves a condensation between adequate substituted Bfx and alkene-type substructure synthons, particularly enamine and enolate nucleophiles. The Beirut reaction has been employed to prepare quinoxaline 1,4-dioxides [41], phenazine 5,10-dioxides (see Chap. Quinoxahne 1,4-dioxide and Phenazine 5,10-dioxide. Chemistry and Biology ), 1-hydroxybenzimidazole 3-oxides or benzimidazole 1,3-dioxides, when nitroalkanes have been used as enolate-producer reagent [42], and benzo[e] [ 1,2,4]triazine 1,4-dioxides when Bfx reacts with sodium cyan-amide [43-46] (Fig. 4). [Pg.271]

Nitromethylation of aldehydes has been carried out in a one pot procedure consisting of the Henry reaction, acetylation, and reduction with sodium borohydride, which provides a good method for the preparation of l-nitroalkanes.16b 79 It has been improved by several modifications. The initial condensation reaction is accelerated by use of KF and 18-crown-6 in isopropanol. Acetylation is effected with acetic anhydride at 25 °C and 4-dimethylaminopyridine (DMAP) as a catalyst. These mild conditions are compatible with various functional groups which are often... [Pg.44]

Condensation of glyoxalic acid, nitroalkanes, and amines provides a simple method for P-nitro-a-amino acids (Eq. 4.116).154... [Pg.107]

The condensation reaction of neat carbonyl compounds with nitroalkanes to afford nitroalkenes, Henry reaction, also proceeds rapidly via this MW approach in the presence of only catalytic amounts of ammonium acetate, thus avoiding the use of a large excess of polluting nitrohydrocarbons normally employed (Scheme 6.22) [72],... [Pg.193]

P. Bako, A. Szolloy, P. Bombicz, L. Toke, Asymmetric C-C Bond Forming Reactions by Chiral Crown Catalysts Darzens Condensation and Nitroalkane Addition to the Double Bond , Synlett 1997, 291-292. [Pg.142]

The mechanisms of the condensation and many other reactions of nitroalkanes are formulated nowadays in terms of carbanions, as in the case of reactions involving CH activated by other groups6. The ion generated from a nitroalkane by the action of base is regarded as a resonance hybrid e.g. for nitromethane ... [Pg.483]

Aliphatic and alicyclic ketones condense with primary nitroalkanes under the influence of A,A-dimethylethylenediamine to yield ally lie nitro compounds as mixtures of geometrical isomers, e.g. equation 125408. [Pg.605]

The nitroaldol condensation reaction involving aldehydes and nitronates, derived from deprotonation of nitroalkanes by bases. [Pg.293]

Aliphatic nitroalkanes can be categorized into six basic groups primary, secondary and tertiary nitroalkanes, terminal and internal gem-dinitroalkanes, and trinitromethyl compounds. Primary and secondary nitroalkanes, and terminal gem-dinitroalkanes, have acidic protons and find particular use in condensation reactions for the synthesis of more complex and... [Pg.1]

Primary and secondary nitroalkanes, and substrates containing terminal em-dinitroaliphatic functionality, have one or more acidic a-protons, a consequence of inductive and resonance effects imposed by the nitro group. As a result, such compounds can behave like carbanions and participate in a number of addition and condensation reactions which are typical of substrates like ketones, aldehydes, and /S-ketoesters. Such reactions are extremely useful for the synthesis of functionalized polynitroaliphatic compounds which find potential use as explosives, energetic oligomers and plasticizers. [Pg.33]

Henry reactions have been extensively exploited for the synthesis of nitrate ester explosives. The condensation of nitroalkanes with aldehydes, followed by esterification of the hydroxy groups with nitric acid, leads to a number of nitrate ester explosives (see Chapter 3). The two examples given above (166 and 167) are synthesized from the C-nitration of the polyols obtained from the condensation of formaldehyde with nitromethane and nitroethane respectively. [Pg.46]

Nitroalkanols are intermediate compounds that are used extensively in many important syntheses 142). They can be converted by hydrogenation into / -aminoalcohols, which are intermediates for pharmacologically important chemicals such as chloroamphenicol and ephedrine. They are obtained by Henry s reaction by the condensation of nitroalkanes with aldehydes. The classical method for this transformation involves the use of bases such as alkali metal hydroxides, alkoxides, Ba(OH)2, amines, etc. 142-144). However, these catalysts give predominantly dehydrated products—nitroalkenes— which are susceptible to polymerization (Scheme 16). The reaction proceeds by the nucleophilic addition of the carbanion formed by the abstraction of a proton from the nitro compound to the carbon atom of the carbonyl group, finally forming the nitroaldol by abstraction of a proton from the catalyst. [Pg.260]

The enolates of other carbonyl compounds can be used in mixed aldol condensations. Extensive use has been made of the enolates of esters, thioesters, amides, nitriles, and nitroalkanes. Scheme 2.4 gives a selection of such reactions. [Pg.68]

The carbon nucleophiles in amine-catalyzed reaction conditions are usually rather acidic compounds containing two electron-attracting substituents. Malonic esters, cyanoacetic esters, and cyanoacetamide are examples of compounds which undergo condensation reactions under Knoevenagel conditions.115 Nitroalkanes are also effective nucleophilic reactants. The single nitro group sufficiently activates the a hydrogens to permit deprotonation under the weakly basic conditions. Usually, the product that is isolated is... [Pg.100]

The reaction is usually carried out in acid solution, but may also be base catalysed. This is the condensation between aldehydes, ammonia or a primary or secondary amine and a compound containing at least one active hydrogen atom e.g., ketones, b-ketoesters, b-cyanoesters, nitroalkanes, alkynes with C°H). For example. [Pg.226]

Cyclic alkyl nitronates may be used in tandem [4+2]/[3+2] cycloadditions of nitroalkanes, and this reaction has been extensively studied by Denmark et al. (64,333-335). In recent work, they developed the silicon-tethered heterodiene-alkene 219 (Scheme 12.63). Steric hindrance and the fact that both the nitroalkene and the a,p-unsaturated ester in 219 are electron deficient renders the possibility of self-condensation. Instead, 219 reacts with the electron-rich chiral vinyl ether 220 in the presence of the catalyst 224 to form the intermediate chiral nitronate 221. The tandem reaction proceeds from 221 with an intramolecular 1,3-dipolar cycloaddition to form 222 with 93% de. Further synthetic steps led to the formation of ( )-detoxinine 223 (333). A similar type of tandem reaction has also been applied by Chattopadhyaya and co-workers (336), using 2, 3 -dideoxy-3 -nitro-2, 3 -didehydrothymidine as the starting material (336). [Pg.863]

The possibility of an attack by the drying agent on the compound to be dried must always be considered carefully and if necessary examined by small-scale tests, as has been mentioned before. Most notable for such unwanted aggression amongst the popular drying agents is the molecular sieve. Various grades of molecular sieve have different activities and specialist publications should be consulted for details. The main reactions which must be kept in mind are that they can catalyse the dehydrochlorination of alkyl chlorides and the condensation of ketones, they can dehydrate alcohols and can form exposive compounds from nitroalkanes (see Section 4.6.3.). [Pg.141]

Nucleophilic addition to C=0 (contd.) ammonia derivs., 219 base catalysis, 204, 207, 212, 216, 226 benzoin condensation, 231 bisulphite anion, 207, 213 Cannizzaro reaction, 216 carbanions, 221-234 Claisen ester condensation, 229 Claisen-Schmidt reaction, 226 conjugate, 200, 213 cyanide ion, 212 Dieckmann reaction, 230 electronic effects in, 205, 208, 226 electrons, 217 Grignard reagents, 221, 235 halide ion, 214 hydration, 207 hydride ion, 214 hydrogen bonding in, 204, 209 in carboxylic derivs., 236-244 intermediates in, 50, 219 intramolecular, 217, 232 irreversible, 215, 222 Knoevenagel reaction, 228 Lewis acids in, 204, 222 Meerwein-Ponndorf reaction, 215 MejSiCN, 213 nitroalkanes, 226 Perkin reaction, 227 pH and, 204, 208, 219 protection, 211... [Pg.211]


See other pages where Nitroalkanes condensation is mentioned: [Pg.126]    [Pg.71]    [Pg.279]    [Pg.126]    [Pg.71]    [Pg.279]    [Pg.76]    [Pg.1189]    [Pg.147]    [Pg.379]    [Pg.203]    [Pg.165]    [Pg.53]    [Pg.164]    [Pg.265]    [Pg.197]    [Pg.198]    [Pg.203]    [Pg.150]    [Pg.175]    [Pg.316]   
See also in sourсe #XX -- [ Pg.147 ]




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