title: Acylation through Ketene Intermediates.
abstract: Carboxylic acids possessing a strong electron-withdrawing group in the alpha-position undergo facile dehydration upon reaction with carbodiimides to form the corresponding substituted ketenes that can react in situ with alcohols providing esters in a high yield. The ketene formed by the treatment of ethyl 2-methylmalonate with DCC was trapped in situ by a [4+2] cycloaddition with a second DCC molecule. The chemoselectivity of the acylation through the ketene intermediates was found to be substantially different from that of conventional acylation reagents showing a very low sensitivity toward the steric bulk of alcohols. A comparison of the sensitivity of the acylation to the steric bulk of alcohols supports the presence of a pseudopericyclic pathway for the nucleophilic addition of alcohols to ketenes derived from ethyl malonic and diethylphosphonoacetic acid.
authors.affiliation: Department of Organic Chemistry, The Hebrew University of Jerusalem, Israel.
authors.forename: Rimma
authors.initials: R
authors.lastname: Shelkov
authors.forename: Moshe
authors.initials: M
authors.lastname: Nahmany
authors.forename: Artem
authors.initials: A
authors.lastname: Melman