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Solid‐state formation of centrosymmetric cage dimeric 4‐aryl‐1,4‐dihydropyridines via non‐symmetric syn‐dimers studied by 13C cross‐polarization magic angle spinning NMR spectroscopy

The solid‐state formation of a centrosymmetric cage dimeric 4‐aryl‐1,4‐dihydropyridine was monitored by 13C cross polarization magic angle spinning (CP/MAS) NMR spectroscopy. The spectra of the photodimerizing derivatives document the changes in symmetry during the reaction and the reaction progress. Furthermore, they clearly reflect characterizing conformational properties of the molecules. Starting from centrosymmetric pairs of monomeric molecules, dimerization proceeds to non‐symmetrical syn‐dimers, that subsequently cyclize to centrosymmetric cage dimers. Thus the application of 13C CP/MAS NMR spectroscopy proves an unusual symmetry breaking in solid‐state photodimerization. Copyright © 1999 Society of Chemical Industry