Environmentally Benign and Scalable Preparation ofDiethyl Furoxan-3,4-dicarboxylate Using Silver Carbonate as a NitrileOxide Generator

Diethyl furoxan-3,4-dicarboxylate (1) is a starting material for many heterocyclic compounds containing furoxan and furazan rings. In general, furoxan 1 was prepared via a dimerization of corresponding nitrile oxide generated either by treatment of ethyl 2-chloro-2-(hydroxyimino)acetate (2) with triethylamine, or by nitration or conversion of -activated ethyl acetate with acetyl nitrate in acetic acid or other catalytic reagents. Both methods are suitable for small-scale but suffered from various drawbacks for large-scale preparation. Years ago, a general method for the preparation of furoxan from corresponding hydroximidoyl chloride (R-CCl=NOH) with silver carbonate (Ag2CO3) was developed in our group. Now this method is extended to prepare 1 from 2. The synthesis involves the treatment of 2 with Ag2CO3 in THF at room temperature, 3-4 h reaction time, with a yield of 80-90%. Using this procedure, a one pound-batch of the material has been prepared at the lab-scale, but the preparation should be easily s...