VERSATILE DOMINO SYNTHESIS AFFORDING NOVEL S-SHAPED AND U-SHAPED TERPYRIDINES - SYNTHESIS, PROPERTIES AND CRYSTAL-STRUCTURE

The development of a simple and general method for the preparation of multifunctional terpyridines is described. The treatment of the ketone s 1a-g with ternary iminium salts results in the formation of the isom eric terpyridines 6 and 8 (according to a domino reaction). A possible reaction mechanism is discussed. In some cases the isolation of the p ostulated dihydropyridine intermediates was successful. The isolation of the 1,4-dihydropyridines 5e, 5j, and 5r (donor-substituted) is surp rising, because most of the stable dihydropyridines are acceptor-subst ituted. In several cases the yields of such domino reactions are very high (>80%). Whether S- or U-shaped terpyridines are formed is immedia tely recognized by NMR spectroscopy. Some special cases (8c, 8e, 6h) w ere investigated by means of single-crystal X-ray analysis.