Chiral photochemistry within zeolites

Chiral induction of chemical reactions continues to be one of the main conc erns of chemists. While basic rules of chiral induction of thermal reaction s have been reasonably established, the same is not true of photochemical r eactions. Short excited state lifetime and low activation energies for reac tions in the excited state(s) leave very little room for manipulating the d iastereomeric transition states. Yet impressive chiral induction of photoch emical reactions in the solid state has been achieved. On the other hand, c hiral induction of photoreactions of organic molecules in solution continue s to be inefficient at ambient conditions. We are exploring the possibility of employing zeolites as a media for achieving chiral induction during pho toreactions. The motivating force for such an attempt is the fact that chir al chemistry in the solid state is not completely general due to the fact t hat not all molecules crystallize. To achieve chiral induction one needs a chiral perturber. Zeolites are not chiral and therefore the perturber is ad ded to the medium. Thus the medium for a photoreaction is a chirally modifi ed zeolite. Of the several reactions investigated, results on photoelectroc ylization of tropolone alkyl ethers are discussed at length. The confined s pace offered by the: zeolite supercage forces a reactant and the chiral ind uctor to interact intimately to yield enantiomerically enriched product. Du e to the transitory nature of the reaction cavity in solution such close in teractions are less likely in isotropic solvent media. The examples discuss ed herein show negligible chiral induction in solution, whereas in a zeolit e one obtains induction as high as 90%.