Microwave-Assisted Ester Formation Using O-Alkylisoureas: A Convenient Method for the Synthesis of Esters with Inversion of Configuration
摘要:
The formation of carboxylic esters via reaction of carboxylic acids with O-alkylisoureas proceeds in excellent yields with very short reaction times when conducted in a monomode microwave synthesizer. Efficient processes were developed using preformed or commercially available isoureas derived from primary and secondary alcohols, with a reaction time of only 5 min or less. It was demonstrated that under these microwave conditions, ester formation proceeded in good yields with clean inversion of configuration where appropriate. The process was validated using menthol, a hindered substrate for S(N)2 reactions. In addition, starting from primary alcohols, ester formation was successfully accomplished using ail in situ isourea formation procedure. A polymer-assisted solution-phase procedure was also developed by employing preformed solid-supported isoureas and by an efficient "catch and release" ester formation procedure whereby primary alcohols were caught on resin as isoureas by reaction with immobilized carbodiimide and released as esters by subsequent treatment with a carboxylic acids.
A Novel Synthesis of 2-Alkylthiobenzothiazoles and 2-Alkylthiobenzoxazoles
作者:Yanfei Yu、Zhengning Li、Lan Jiang
DOI:10.1080/10426507.2011.636229
日期:2012.5
3H-Benzothiazole-2-thione and 3H-benzoxazole-2-thione were selectively S-alkylated by use of O-alkylisoureas as the alkylating reagents. The reactions could be performed under mild reaction conditions in short reaction times, and high yields were obtained using O-primary-alkylisoureas, whereas low yields were obtained with sec- and tert-alkylisoureas.
COLLINGWOOD, STEPHEN P.;DAVIES, ALAN P.;GOLDING, BERNARD T., TETRAHEDRON LETT., 28,(1987) N 38, 4445-4448
作者:COLLINGWOOD, STEPHEN P.、DAVIES, ALAN P.、GOLDING, BERNARD T.
DOI:——
日期:——
Microwave-Assisted Ester Formation Using <i>O</i>-Alkylisoureas: A Convenient Method for the Synthesis of Esters with Inversion of Configuration
The formation of carboxylic esters via reaction of carboxylic acids with O-alkylisoureas proceeds in excellent yields with very short reaction times when conducted in a monomode microwave synthesizer. Efficient processes were developed using preformed or commercially available isoureas derived from primary and secondary alcohols, with a reaction time of only 5 min or less. It was demonstrated that under these microwave conditions, ester formation proceeded in good yields with clean inversion of configuration where appropriate. The process was validated using menthol, a hindered substrate for S(N)2 reactions. In addition, starting from primary alcohols, ester formation was successfully accomplished using ail in situ isourea formation procedure. A polymer-assisted solution-phase procedure was also developed by employing preformed solid-supported isoureas and by an efficient "catch and release" ester formation procedure whereby primary alcohols were caught on resin as isoureas by reaction with immobilized carbodiimide and released as esters by subsequent treatment with a carboxylic acids.
Conversion of alcohols into alkyl bromides and iodides via O-alkylisoureas
作者:Stephen P. Collingwood、Alan P. Davies、Bernard T. Golding
DOI:10.1016/s0040-4039(00)96534-1
日期:1987.1
Treatment of O-alkylisoureas with trifluoromethanesulphonic acid and a tetrabutylammonium salt (bromide or iodide) affords alkyl halides in high yields.