Solvents alkoxycarbonylation

Olah s original preparative nitrations were carried out with mixtures of the aromatic compound and nitronium salt alone or in ether, and later with sulpholan as the solvent. High yields of nitro-compounds were obtained from a wide range of aromatic compounds, and the anhydrous conditions have obvious advantages when functional groups such as cyano, alkoxycarbonyl, or halogenocarbonyl are present. The presence of basic fimctions raises difficulties with pyridine no C-nitration occurs, i-nitropyridinium being formed. ... 

An efficient chemoenzymatic route for the synthesis of optically active substituted indolines has been recently developed (Scheme 7.27), and also the alkoxycarbonyla-tion process is more efficient than the acylation reaction. Different lipases have been tested in the alkoxycarbonylation of these secondary amines, GALA being found to be the best biocatalyst for 2-substituted-indolines, and CALB for 3-methylindoline. The combination of lipases with a variety of allyl carbonates and TBME as solvent has allowed the isolation of the carbamate and amine derivatives in a high level of enantiopurity [51]. 

In 1986, Tsuji et al. developed the palladium(0)-catalyzed alkoxycarbonylation of racemic or achiral propargyl carbonates 128 in an alcohol solvent to afford 131 via carbonylation of 129 to 130 (Scheme 4.35) [55], Palladium(0)-catalyzed alkoxycarbonylation of 134 and isomerization to 136 were key steps for the total synthesis of (-)-kallolide B 138 (Scheme 4.36) [56],... 

Kagan H, Namy JL (1999) Influence of Solvents or Additives on the Organic Chemistry Mediated by Diiodosamarium. 2 155-198 Kakiuchi F, Murai S (1999) Activation of C-H Bonds Catalytic Reactions. 3 47-79 Kakiuchi F, Chatani N (2004) Activation of C-H Inert Bonds. 11 45-79 Kalck P, Urrutigoi ty M, Dechy-Cabaret O (2006) Hydroxy- and Alkoxycarbonylations of Alkenes and Alkynes. 18 97-123 Kanno K, see Takahashi T (2005) 8 217-236 Keen SP, see Gibson SE (n6e Thomas) (1998) 1 155-181 Kendall C, see Wipf P (2005) 8 1-25... 

Interest in the uses of HMPT has also been maintained, but a warning has been issued (by the E. I. du Pont de Nemours Company and the U.S. National Institute for Occupational Safety and Health) about its potential acute toxicity. HMPT has been used in the synthesis of 2,4-bis(dimethylamino)qui nolines,9 8 as a solvent for reactions between carbonyl compounds and sulphur," for the conversion of iV-benzylcarbox-amides into 3-phenylpropionitriles,100 in reactions between metals or organometallic compounds with a variety of organic substrates,101 and as a solvent for alkylation reactions of /J-keto-esters and related compounds in which the alkylation reaction is accompanied by de(alkoxycarbonylation) (Scheme 7).102... 

Ferrero, M., Fernandez, S. and Gotor, V., Selective alkoxycarbonylation of A-ring precursors of vitamin D using enzymes in organic solvents. Chemoenzymatic synthesis of lo ,25-dihydroxyvi-tamin D3 C-5 A-ring carbamate derivatives. J. Org. Chem., 1997, 62, 4358. 

In a similar fashion, palladium-catalyzed alkoxycarbonylation of 54 was effective in producing pyrimdine esters 55 <99T405>. It was noted that dppf along with the use of the alcohols as solvents (rather than solely as reagents) was required for optimal conversion. 

Ionic liquids serve as very useful reaction media, which can facilitate easy separation of product(s) and a catalyst after the reaction. These substitutes of organic solvents as reaction media have already been successfully applied to a variety of transition metal-catalyzed organic reactions such as Heck reaction, Suzuki cross-coupling, hydroformyla-tion, and alkoxycarbonylation. ... 

As is to be expected, an alkynic ketone undergoes a Michael addition with a carbanion, leading eventually to a pyranone (50JA1022). Using malonic esters, a 3-alkoxycarbonyl derivative results, which is hydrolyzed to the 2-oxopyran-3-carboxylic acid under alkaline conditions, but to the pyranone by sulfuric acid. Rapid ester exchange is observed with the initial products, the alcohol used as solvent determining the nature of the alkyl group in the 3-carboxylic esters (Scheme 90). 

The course of the reaction between DMAD and alkoxycarbonyl-cyanopyridinium methylides (79 X = CN, Y = C02R) is strongly solvent dependent.284 In dimethylformamide or benzene, indolizines (e.g., 80) are obtained, but in acetonitrile the reaction is stated to give 81, an ester shift285 having taken place. Douglass and Wesolosky286 reacted the ylids 79 (X = E, Y = CN) with DMAD and isolated 82. 

H-NMR studies have demonstrated that, depending on the substitutents and solvent, the 9-alkoxycarbonyl, 9-carbamoyl, or 9-formyl derivatives of 4-oxo-tetrahydro-4/f-pyrido[l,2-a]pyrimidines exist as (5,7,8,9- and/or... 

R BT, R2 = H) the equilibrium mixture is 232 (45%) and 233 (55%). 3-Hydroxythiophene 233 (R1 = R2 = H), prepared from the trimethylsilyl ether, is sufficiently stable for its 1H NMR spectrum to be obtained in a variety of solvents <1989JA5346>. In CC14 both tautomers are observed, contrary to an earlier report where only the oxo form was observed <1986TL5155>. Electron-withdrawing substituents, such as alkoxycarbonyl, generally cause the hydroxy form to predominate <1965T3331>. 

The spectra of 2-alkoxycarbonyl-3-aminoacrylic esters (73, R1 = H, alkyl, aryl) show that these substances exist in the enamino-ester form with a strong intramolecular hydrogen bond between the amino and COOR2 groups. Conformers 73a (Z, Z, E) and 73b (E,Z,E) predominate in non-polar media conformation 73b is also probably present in polar solvents and is preferred in the solid state109. (The symbols indicate, in the order shown, the alignments of the free C=0, the bonded C=0 and the R1 group with respect to the carbon-carbon double bond.)... 

However, in 1972, one year before Manassen s and Joo s first publications, Parshall working at Dupont in Delaware reported that the hydrogenation and alkoxycarbonylation of alkenes could be catalysed by PtCL when dissolved in tetraalkylammonium chloride/tin dichloride at temperatures of less than 100°C/5] It was even noted that the product could be separated by decantation or distillation. Parshall recognised the separation problem associated with homogeneous catalysis and in this paper states, An approach that seems under utilised is the use of molten salts as stable, non-volatile solvents from which organic products are readily separated by distillation. .. or decantation . An even earlier report by a group working for the U S. 

Detritylation. Trityl ethers are rapidly cleaved at ro< m temperature in 85-95% yield by the complex of BF with methanol or by BF, etherate and methanol in aprotic, anhydrous solvents (CH2CI2, C6H6>. O- and IST-Acyl groups, O-sulfonyl, N-alkoxycarbonyl, O-methyl, O-benzyl, and acetal groups are stable under these conditions. ... 

Azodicarboxylates are recognized for their ability to participate as 2ir components of HOMOdi e-con-trolled Diels-Alder reactions with dienes and for their participation in ene reactions with reactive al-kenes. 489 j, addition, electron-rich or reactive simple alkenes that do not contain a reactive allylic hydrogen atom have been shown to participate in competitive [2 + 2] and [4 + 2] cycloaddition reactions with azodicarboxylates in which the observed course of the reaction is dependent upon the solvent polarity and nucleophilic character of the alkene (Table 13). As may be anticipated, alkoxycarbonyl-aroyldiimides (4), diaroyldiimides (5), and aiylaroyldiimides (6) participate with increasing selectivity as 4tr components of [4 + 2] cycloaddition reactions. 

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