Photocatalysis for Organic Synthesis

This project aims to develop new synthetic methodologies for selected reactions of relevance to the pharmaceutical industry based on heterogeneous photo-catalysis.

Titania (tioxide) has achieved international prominence for its role in the destructive oxidation of organic molecules during environmental remediation in sterilizing, anti-fouling, self-cleaning etc. uses. We discovered that it can also be used in an unconventional way in constructing useful compounds. Free radicals are generated that can couple together, add to olefins and build rings. These processes are simple, cheap and environmentally friendly. There is potential to develop green technology for making useful organic compounds.

Our new unconventional titania photocalyses work with with unprocessed carboxylic acids. As a heterogeneous catalyst titania is cheap, easily separated by filtration and safe; no hard UV is needed. The carboxylic acids can be used directly without any special functionalization so the syntheses are very user-friendly. In exploring this chemistry we uncovered several interesting and intriguing aspects. Used without a reaction partner, carboxylic acids decarboxylated and then selectively produced high yields of homo-dimeric products. Alkoxymethyl and aryloxymethyl radicals were generated particularly efficiently. We successfully deployed them in convenient alkylations of electron-deficient alkenes. We also discovered a remarkable cascade reaction in which phenoxyacetic acid reacts with maleic anhydride or a maleimide to yield chromenedione derivatives. Furthermore, by judicious modifications of the catalyst and reaction conditions, this process could be directed either to yield the chromenediones or to produce the alkylated alkenes. In short, we showed that our “clean” anaerobic TiO2-based method has great potential for original syntheses and for making many of the molecules usually associated with toxic organotin methodology.