Reaction of spiro [piperidine-4,2′-(1′,2′,3′,4′-tetrahydroquinazolin)]-4′-ones with acetic anhydride

The tetrahydro derivative (5a) and its aza derivative (5b) of antitumor active amsacrine were prepared. The key synthetic intermediate (3a) was simply prepared by rearrangement of spiro-compound (2a) by heating with acetic anhydride and pyridine. On the other hand, another key intermediate (3b) was obtained only during moderated reaction conditions, and the ring opening products (6b,b′ and 8b,b′) were obtained under the usal conditions.