Wednesday, June 25, 2008
Congressional Room (Capital Hilton)

Photo-Induced Solid State Absolute Asymmetric Synthesis In Nanocrystalline Suspensions

Farnosh Family and Miguel Garcia-Garibay. University of California, Los Angeles, CA

Solid state photochemistry has tremendous potential as a green chemistry methodology to obtain enantiomerically enriched chiral products. However, further improvements can be made through the use of nanocrystalline suspensions in environmentally benign water. By reducing the size of the crystals to about 200 nm and starting from chiral crystals, we have improved the enantiomeric excess of several photochemical absolute asymmetric reactions. One reaction examined by this process is the di-g methane reaarangement of a dibenzobarralene ester which can crystallize in a chiral space group. Previous reports of the reaction showed a maximum %ee at 30% conversion where the reaction stops due to the crystal lattice breaking down. In this study, we found that grinding chiral crystals and creating suspensions in water created a 65% ee at 85% conversion. Another example is the electrocyclization of 2-pyridinone derivatives. Meta-substitution on the benzyloxy attached at the 4 position of the 2-pyridinone created crystals that packed in chiral space groups. Using solely the chiral information in the crystal, an enantiomeric excess was created