Abstract: | Reaction of N‐deacetylthiocolchicine ( 3 ) and N‐deacetylcolchicine ( 4 ) with nitrous acid (HONO) furnished the new tetracyclic colchicinoids 5 and 6 , as well as the Demyanov‐rearrangement products 7 and 8 . Starting from 3 , the pyrazole‐containing tetracycle 9 was obtained. The novel compounds were characterized spectroscopically, and an X‐ray crystal‐structure analysis of 5 allowed us to establish the absolute configurations at the stereogenic centers. |