ASYMMETRIC INDUCTION IN THE PHOTOCHEMISTRY OF CRYSTALLINE SALTS - STRUCTURE-REACTIVITY CORRELATIONS

The enantioselectivity of the di-pi-methane photorearrangement was stu died in chiral crystals. Achiral dibenzobarrelene acids 1 and 2 were f orced to crystallize as chiral crystals by salt formation with chiral amines. Photolysis of these salts in the solid state yielded photoprod ucts in > 95% enantiomeric excess. The absolute configurations of the salts and their photoproducts were determined. This allowed the absolu te steric course of the di-pi-methane reaction to be mapped and the st ructural features that control the enantioselectivity to be identified . In contrast to the solid state photolyses, irradiations in solutions give only racemic photoproducts, presumably because the salts dissoci ated.