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 an 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.
Esterification O 0315Microwave-Assisted Ester Formation Using O-Alkylisoureas: A Convenient Method for the Synthesis of Esters with Inversion of Configuration. -Efficient formation of esters can also be achieved by in situ generation of O-alkylisoureas. Polymer-supported reactions are also described. -(CHIGHINE, A.; CROSIGNANI, S.; ARNAL, M.-C.; BRADLEY, M.; LINCLAU*, B.; J. Org. Chem. 74 (2009) 13, 4753-4762; Sch. Chem., Univ. Southampton, Southampton SO17 1BJ, UK; Eng.) -Jannicke 49-044
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.