Abstract The cyclization rate constants have been measured of substituted ethyl N- (phenylaminocarbonyl)-, N-(alkylaminocarbonyl)-, and N-(phenylaminothiocarbonyl) glycinates RNHCXNHCH 2 CO 2. C 2 H 5 (X= O, S). Logarithms of these constants increase with decreasing basicity of the amines down to the value of pK a (RNH 2)= 5.5. The rate- limiting step of the reaction is formation of the tetrahedral intermediate. With ethyl N-( ...