Intramolecular [2 + 2] Photocycloaddition of Vinylarenes: Synthesis of Cyclophanes

Intramolecular [2 + 2] photocycloaddition reactions were successfully applied to the synthesis of cyclophanes, although the photocyclodimerization of styrene gave a meager yield. Many cyclophanes, including para-, meta-, and orthocyclophanes, cyclonaphthalenophanes, biphenylophanes, naphthalenophanes, and phenanthrenophanes, were prepared from corresponding vinylarenes in reasonable yields. Some cyclophanes were used as ionophores or receptors and precursors for some interesting materials. The present account is focussed on the scope and limitation of this reaction toward cyclophanes. 1. Introduction 2. Factors Affecting the Photocyclization of Styrene Derivatives 2.1. Aromatic Nuclei 2.2. Chain Length between Vinylarene Moieties 2.3. Functional Groups on Vinyl Groups 2.4. Functional Groups on Aromatic Nuclei 3. Further Transformations of the Phanes 3.1. Benzocyclobutene Homologs from Cyclophanes 3.2. Calixarene Analogs from Cyclophanes 3.3. Ring Inversion of Naphthalenophanes by Birch Reduction 3.4. Further Photoreactions of the Phanes 4. Conclusion