Structural aspects of the product from glyoxal and tetrakis(ethoxycarbonylamino)ethane

The base-promoted addition of glyoxal to 1,1,2,2-tetrakis(ethoxycarbonylamino)ethane in DMF gives a product mixture containing mostly 1,1′,3,3′-tetrakis(ethoxycarbonyl)-4,4′,5,5,'-tetrahydroxy-2,2′-biimidazolidyl. An alternate structure containing a tetraazadecalin system was considered less likely, since the most significant peak in the mass spectrum of this product and a tetraacetate derivative corresponded to half the mass of the parent ion. Two-dimensional nmr spectra on the major hplc fraction are more consistent with the biimidazolidinyl structure (very low J_vic and lack of NOE enhancement). A HETCOSY spectrum on the mixture allowed assignment of ¹H nmr shifts.