PHOTOCHEMICAL METHODS<br>Photochemistry and Organic Synthesis<br>Irradiation Apparatus<br>Further Experimental Parameters<br>Photochemical Steps in Synthesis<br>CARBON-CARBON BOND FORMATION BY PHOTOELIMINATION OF SMALL MOLECULES IN SOLUTION AND IN CRYSTALS<br>Introduction<br>Photochemical C-C Bond Formation in Solution<br>Reactions in the Solid State<br>Conclusions<br>INTERMOLECULAR ADDITION REACTIONS ONTO C-C MULTIPLE BONDS<br>Introduction<br>Addition to C-C Double Bonds<br>Addition to C-C Triple Bonds<br>Conclusions<br>FORMATION OF A 3-MEMBERED RING<br>Introduction<br>Di-Pi-Methane Rearrangement<br>Oxa-Di-Pi-Methane Rearrangement and Related Rearrangements<br>[2+1] Cycloaddition of Alkenes with Carbenes<br>Formation of a Cyclopropane Via Intramolecular Hydrogen Abstraction<br>[3+2] Cycloaddition of Arenes with Alkenes<br>Photochemical Synthesis of Three-Membered Heterocycles<br>FORMATION OF A 4-MEMBERED RING I<br>Introduction<br>[2+2]-Photocycloaddition of Non Conjugated Alkenes<br>[2+2]-Photocycloaddition of Aromatic Compounds<br>Photochemical Electrocyclic Reactions<br>Intramolecular Gamma-Hydrogen Abstraction (Yang Reaction)<br>Metal Catalyzed Reactions<br>Various Methods<br>Conclusions<br>FORMATION OF A 4-MEMBERED RING II<br>Introduction<br>[2+2]-Photocycloaddition of Enones (Substrate Type A1)<br>[2+2]-Photocycloaddition of Vinylogous Amides and Esters (Substrate Clases A2 and A3)<br>[2+2]-Photocycloaddition of Alpha, Beta-Unsaturated Carboxylic Acid Derivatives (Substrate Classes A4, A5 and A6)<br>Conclusions and Perspectives<br>FORMATION OF A 4-MEMBERED RING III (OXETANES)<br>Introduction<br>Generally Accepted Mechanisms of the Paternò-Büchi Reaction<br>Regio- and Siteselective Synthesis of Oxetanes<br>Stereoselective Syntheses of Oxetanes<br>Conclusive Remarks<br>FORMATION OF A 5-MEMBERED RING<br>Formation of Five-Membered Ring: Intramolecular Delta-H Abstraction<br>Formation of Five-Membered Rings Via [3+2]-Cycloadditions<br>Photochemical Electrocyclization Reactions: Synthesis of Fused Five-Membered Ring Compounds<br>Photoinduced Electron Transfer Radical Cation Mediated Cyclizations: Synthesis of Five-Membered Carbocyclic as well as Heterocyclic Ring Systems<br>FORMATION OF 6-MEMBERED RING (AND LARGER RINGS)<br>Introduction<br>Photoelectron Transfer Initiated Cyclizations<br>Photoinduced 6Pi-Electrocyclization<br>Photocycloaddition Reactions<br>Remote Intramolecular Hydrogen Abstraction<br>Ring Contraction and Ring Enlargement<br>Other Reactions<br>Summary<br>AROMATIC AND HETEROAROMATIC SUBSTITUTION BY SRN1 AND SN1 REACTIONS<br>Introduction<br>General Mechanistic Features<br>Carbon-Carbon Bond Formation<br>Carbon-Heteroatom Bond Formation<br>Synthesis of Bi, Tri, and Poliaryls<br>Synthesis of Carbocycles and Heterocycles<br>SINGLET OXYGEN AS A REAGENT IN ORGANIC SYNTHESIS<br>Introduction<br>Dioxetanes<br>Endoperoxides<br>Allylic Hydroperoxides<br>Tandem Singlet Oxygen Reactions<br>Conclusion<br>SYNTHESIS OF HETEROAROMATICS VIA REARRANGEMENT REACTIONS<br>Introduction<br>Synthesis of Five-Membered Rings with One Heteroatom<br>Synthesis of Five-Membered Rings with Two Heteroatoms<br>Synthesis of Five-Membered Rings with Three Heteroatoms<br>Synthesis of Six-Membered Rings<br>Synthesis of Seven-Membered Rings<br>Concluding Remarks<br>PHOTOLABILE PROTECTING GROUPS IN ORGANIC SYNTHESIS<br>Introduction<br>Photolabile Protecting Groups<br>Chromatic Orthogonality<br>Two-Photons Absorption<br>Perspectives and Conclusion<br>