- Trapping of carbamic acid species with (trimethylsilyl)diazomethane
-
Methoxycarbonylation of a variety of amines into the corresponding methyl carbamates was accomplished by allowing them to react with (trimethylsilyl) diazomethane TMSCHN2 under bubbling of CO2. The reaction was performed at room temperature for a period of ca. 2 h in benzene-MeOH (4/1 v/v), which was the solvent of choice. In this mixed solvent, undesirable bicarbonate is formed in equilibrium along with carbamate anion. Owing to the irreversibility in the esterification step by TMSCHN2, however, the yield of methyl carbamate can reach very high.
- Ito, Yoshikatsu,Ushitora, Hiromi
-
p. 226 - 235
(2007/10/03)
-
- Synthesis of methyl carbamates from primary aliphatic amines and dimethyl carbonate in supercritical CO2: Effects of pressure and cosolvents and chemoselectivity
-
(Chemical Equation Presented) At 130 °C, in the presence of CO 2 (5-200 bar), primary aliphatic amines react with dimethyl carbonate (MeOCO2Me, DMC) to yield methyl carbamates (RNHCO2Me) and N-methylation side-products (RNHMe and RNMe2). The pressure of CO2 largely influences both the reaction conversion and the selectivity toward urethanes: in general, conversion goes through a maximum (70-80%) in the midrange (40 bar) and drops at lower and higher pressures, whereas selectivity is continuously improved (from 50% up to 90%) by an increase of the pressure. This is explained by the multiple role of CO2 in (i) the acid/base equilibrium with aliphatic amines, (ii) the reactivity/solubility of RNHCO2- nucleophiles with/in DMC, and (iii) the inhibition of competitive N-methylation reaction of the substrates. Cosolvents also affect the reaction: in particular, a drop in selectivity is observed with polar protic media (i.e., MeOH), plausibly because of solvation effects (through H-bonds) of RNHCO2- moieties. The reaction shows also a good chemoselectivity: bifunctional aliphatic amines bearing either aromatic NH2 or OH substituents [XC6H4(CH2)nNH2, X = NH2, OH; n = 1 2], undergo methoxycarbonylation reactions exclusively at aliphatic amino groups and give the corresponding methyl carbamates [XC 6H4(CH2)nNHCO2Me] in 39-65% isolated yields.
- Selva, Maurizio,Tundo, Pietro,Perosa, Alvise,Dall'Acqua, Federico
-
p. 2771 - 2777
(2007/10/03)
-
- Process for the production β-amino-α-hydroxycarboxylic acids and derivatives thereof
-
Disclosed is a process for producing β-amino-α-hydroxycarboxylic acid derivatives of general formula (2R,3S)- or (2S,3E)-N-(X,Y)-3-amino-2-hydroxy-3-phenyl propionic acid-Z of Formula I, STR1 e.g. of (2E,3S)-3-amino-2-hydroxy-3-phenyl propionic acid or (2R,3S)-N-benzoyl-3-amino-2-hydroxy-3-phenyl propionic acid methylester. Compounds of type I are valuable intermediates in the total synthesis of Taxols which can be used in the treatment of various forms of cancer.
- -
-
-
- A convenient method for synthesis of optically active β-hydroxyamines from primary amines through enecarbamates as key intermediates
-
This report describes a new method to prepare optically active β-hydroxamines starting from primary amines. The method consists of a transformation of N-methoxycarbonylated primary amines to the corresponding enecarbamates utilizing electrochemical oxidat
- Matsumura, Yoshihiro,Ohishi, Takahiro,Sonoda, Chihiro,Maki, Toshihide,Watanabe, Mitsuaki
-
p. 4579 - 4592
(2007/10/03)
-