Solid-State Photooligomerization of an Extended Chiral Bifunctional Monomer, (+)-2,4:3,5-Di-O-methylene-D-mannitol 1,6-Di-trans-cinnamate

Irradiation of crystalline (+)-2,4:3,5-di-O-methylene-D-mannitol 1,6-di-trans-cinnamate (1) induces intermolecular cyclobutane formation leading to chiral oligomers of increasing length. The dimer, trimer, tetramer, and pentamer have been isolated and characterized. The intramolecular distance between the olefinic residues within the molecules of 1 is larger than in any previous examples of solid-state photodimerization or oligomerization and, in spite of the large, bulky tetraoxa-c/Tdecalin group separating the reaction centers, the cinnamate groups of the monomer are properly aligned for intermolecular photocycloaddition. Crystals of 1 are monoclinic, a = 15.218 (6) Á, b = 13.217 (7) Á, c = 5.882 (3) Á, β = 76.95 (3)°; the space group is P2₁, with two molecules in the cell. The structure has been solved by direct methods and refined to an R factor of 0.043 on 2270 nonzero reflections. The crystal structure analysis establishes the correct molecular structure of the sugar alcohol derivative, previously in doubt, and elucidates the molecular packing which is responsible for the observed products. The chemical consequences of solid-state irradiation of compound 12, a monothiophene analogue of 1, have been considered; 12, however, shows an unexpected reluctance to crystallize in the same structure as 1.