[2 + 2] Topochemical photoreaction is reviewed focussing on the photopolymerization of diolefin crystals.
In α-type crystal of olefin compounds, double bonds make contact at a distance of approximately 4 Å across a center of symmetry and, on photoirradiation it gives a centrosymmetric cyclobutane dimer (1-dimer). A β-type crystal is characterized by a lattice with one axial length of 4Å between translationally related molecules, and gives a dimer of mirror symmetry (
m-dimer). In a typical topochemical photoreaction of these olefin compounds, the reaction proceeds stereospecifically with the retention of space group of the starting crystal.
In the polymerization of α-type diolefin crystals, highly crystalline linear high polymers are obtained in extremely high yields. On the other hand, from the β-type diolefin crystals, crystalline or amorphous oligomers having a zigzag main chain, or cyclophanes are obtained. Topochemical studies of unsymmetric diolefin crystals have revealed a great variety of reaction behaviors and of photoproduct configurations which are influenced strictly by a slight modification of chemical structures. The polymers having new types of alternating chain structures are prepared from unsymmetric diolefin crystals. These polymers are expected to be promising functional materials. The optically active oligomeric substances are prepared from the prochiral unsymmetric diolefin compounds through the topochemical photoreaction of chiral crystal. Lattice energy calculation has been recently applied to explain the structure-reactivity correlation including the exceptional behavior of [2+2] topochemical photoreations.
抄録全体を表示