Our laboratory has uncovered the synthesis of 3-methylene-3,4-dihydroquinoxalin-2(1H)-ones 4 from benzimidazolium-based NHCs and 2-methylsulfonyl-substituted chromones 1, where the NHC-core was converted to the quinoxaline framework. In this conversion, a nucleophilic substitution reaction presumably occurred between 1 and 2 to generate the benzimidazolium-substituted chromone intermediate 3, from which upon addition of an aqueous solution of NaOH, the imidazole ring expanded along with opening of the pyran ring, yielding 4. This class of compounds contains derivatives exhibiting biological activities such as anticancer and antidiabetic activities. Condition screening experiments showed that the reaction between 1 and 2 in DMF or NMP at 25 °C for 1 to 24 hours lead to the complete consumption of the chromone. Subsequent addition of a 5 molar aqueous solution of NaOH and stirring at 5 °C for 18 to 48 hours provided the desired 3,4-dihydroquinoxalin-2(1H)-ones 4 with yields up to 97%. This research provides both evidence for the utility of NHCs as reactants in organic synthesis as well as a novel route towards 3-methylene-3,4-dihydroquinoxalin-2(1H)-ones.

Ring expansion of in situ generated chromonylbenzimidazoliums yielding 3-methylene-3,4-dihydroquinoxalin-2(1H)-ones

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