Unexpected formation of 2,2-dichloro-N-(chloromethyl)acetamides during attempted Staudinger 2,2-dichloro-β-lactam synthesis

S. Deketelaere, E. Van den Broeck, L. Cools, D. Deturck, H. Naeyaert, K. Van Hecke, C. Stevens, V. Van Speybroeck, M. D'Hooghe
European Journal of Organic Chemistry
2021
A1

Abstract 

In the quest for 3,3-dichloro-β-lactam building blocks, the serendipitous formation of 2,2-dichloro- N -(chloromethyl)acetamides was observed. This peculiar reactivity was investigated in detail, both experimentally and computationally by means of Density Functional Theory (DFT) calculations. 2,2-Dichloro-N-(chloromethyl)acetamides were thus shown to be formed experimentally through reaction of 2,2-dichloroacetyl chloride with glyceraldehyde-derived imines, i.e. (2,2-dimethyl-1,3-dioxolan-4-yl)methanimines, bearing aromatic N-substituents, in the presence as well as in the absence of a base. Deployment of aliphatic imines, however, resulted in complex reaction mixtures, pointing to the importance of a stabilizing aromatic substituent at nitrogen. The DFT results indicate that the substituents can alter the governing equilibria on the one hand and intrinsic barrier heights for the different routes on the other hand, showing that these are controlling the reaction outcome. Furthermore, the 2,2-dichloro- N -(chloromethyl)acetamides proved to be rather unstable in solution and thus difficult to isolate. Nonetheless, their molecular structure was confirmed by means of NMR analysis of several purified analogs and X-ray study of a 4-methoxyphenyl derivative.