Collect. Czech. Chem. Commun. 1987, 52, 156-161

Mechanism of base-catalyzed cyclization of ethyl N-(substituted aminocarbonyl)glycinates

Jaromír Mindl and Vojeslav Štěrba

Department of Organic Chemistry, Institute of Chemical Technology, 532 10 Pardubice


The cyclization rate constants have been measured of substituted ethyl N-(phenylaminocarbonyl)-, N-(alkylaminocarbonyl)-, and N-(phenylaminothiocarbonyl)glycinates RNHCXNHCH2CO2.C2H5 (X = O, S). Logarithms of these constants increase with decreasing basicity of the amines down to the value of pKa(RNH2) = 5.5. The rate-limiting step of the reaction is formation of the tetrahedral intermediate. With ethyl N-(phenylaminocarbonyl)glycinates (whose pKa(RNH2) values are higher) this dependence, on the contrary, slightly decreases, and the acid-catalyzed splitting off of ethoxy group from the cyclic intermediate becomes rate-limiting. The cyclization rate of a series of ethyl N-(phenylaminothiocarbonyl)glycinates is practically independent of the pKa(RNH2) values, the change in the rate-limiting step would take place at pH about 9.