An Efficient Synthesis of Tetracyclic Pyrano[ 2,3-d]pyrimidines

[GRAPHICS] A series of pyrano[ 2,3-d] pyrimidine derivatives have been synthesized by the reaction of 2-amino-3cyano- 4H-pyrans and acetic anhydride with acid catalyst. This method is very efficient because of short reaction times and easy work- up, and it provides an efficient and promising synthetic strategy for the construction of the tetracyclic pyrano[ 2,3-d] pyrimidine skeleton. The X-ray crystal structures of products are confirmed, and the possible mechanism is provided in this paper.