Concepts of Stereoselective Photochemistry and a Case Study: the Paterno-Buchi Reaction

The main methods reported in literature to obtain stereoselective photochemical reaction is reviewed. The most important approached attempted to obtain stereoselective photochemical reaction are: 1.) the use of diastereoselective photochemical reactions, 2.) the use of molecules with prevented mobility (this approach can be obtained 1. introducing chiral auxiliary, 2. introducing chiral molecules in the reaction mixture able to give complexes with a reduced mobility, 3. performing the reaction in organized media such as zeolites or cyclodextrins, 4. performing the reaction on single crystal, 5. performing the reaction on single crystals of molecules able to give crystal in chiral space group, and, 6. finally performing the reaction in solid phase on inclusion complexes of the substrate with chiral molecules); 3.) using chiral solvents and chiral light, and 4.) using chiral photosensitizers. The case of the diastereoselective Paternò-Büchi reaction on furan derivatives is also discussed.