Dihydropyridines reacted with a series of alkoxycarbene complexes of chromium and tungsten to give new pyridinium ylid complexes which were fully characterized by X-ray crystallography. They transferred very easily upon elimination of pyridine their alkylidene groups to various olefins to give functionalised cyclopropanes. A second type of nitrogen-ylid complexes resulted from the interaction of aminocarbene complexes of chromium with alkynes: they were shown to undergo transformations related to the Stevens rearrangement of  organic N-ylids, to give polycyclic  N-containing heterocycles among of which alkaloid derivatives.