NOVEL SOLID-STATE SYNTHESIS OF DIMERIC 4-ARYL-1,4-DIHYDROPYRIDINES

On irradiation in the solid state the 4-aryl-1,4-dihydroypridines 1 un dergo [2+2] cycloadditon to centrosymmetric head-to-tail dimers 3 and 4a. The almost exclusive formation of the cage dimers 3 via the C-2-sy mmetric syn-dimers 2 takes place in nearly quantitative yields, in con trast with the cycloaddition reaction of the anti-dimer 4a, which is a ccompanied by photooxidation to pyridine 5a.