Chiral photochemistry within zeolites

The last few decades have seen an abundance of methodologies to carry out ground state reactions stereoselectively. Meanwhile asymmetric photoreactions have not been attempted with the same kind of rigor as thermal asymmetric reactions and have seen a slower advance. It should also be stated that photoreactions involve highly energetic excited states, which generally have very short lifetimes. These short lifetimes are insufficient to develop an effective interaction between the substrate and the chiral source. In ground state reactions, a difference of a few kilocalories between the diastereomeric transition states is enough to give very high stereodifferentiation. The presence of small or negligible activation barriers in photochemical reactions makes them more difficult to control, and imaginative methods have to be developed to carry out these reactions. In spite of the apparent stumbling blocks in the way, advances have been made in the field of asymmetric photoreactions [1-7]. Several methods have been attempted to effect chiral induction in asymmetric photoreactions. Reactions have been phase. The chiral sources employed include circularly polarized light, chiral sensitizers, chiral solvents, chiral substituents, chiral host-guest assemblies, and chiral crystalline environments.