Green hydrothermal synthesis of fluorescent 2,3-diarylquinoxalines and large-scale computational comparison to existing alternatives.

Recently, also first HT syntheses (HTS) of organic compounds were achieved. Here, we report the HTS of 2,3-diarylquinoxalines from 1,2-diketones and o -phenylendiamines ( o -PDAs). The synthesis is simple, fast and generates high yields, without requiring any organic solvents, strong acids or toxic catalysts. Reaction times down to <10 min without decrease in yield can be achieved through adding acetic acid as promoter, even for highly apolar biquinoxalines (more than 90% in all cases) . We show moreover that HTS is compatible with: (i) hydrochlorides, a standard commercial form of amines, can be used directly as combined amine source and acidic catalyst and (ii) Boc-diprotected o -PDA can be directly employed as substrate that undergoes HT deprotection. A systematic large-scale computational comparison of all reported syntheses of the presented quinoxalines from the same starting compounds shows that our method is more environmentally friendly and less toxic than all existing methods, and reveals generic synthetic routes for improving reaction yields. Finally, we explore the application of the synthesized compounds as fluorescent dyes for cell staining.