Reactions of Arylpropynehydrazides with Substituted Malonyl Chlorides: A Route to Pyrazolo-Condensed 1,3-Oxazines

Reaction of phenylpropynehydrazide with dimethylmalonyl chloride furnished the corresponding 4,4‐dimethyl‐1‐(3‐phenylprop‐2‐ynoyl)pyrazolidine‐3,5‐dione, which upon thermolysis underwent a 6‐endo‐dig cyclization to a pyrazolo[5,1‐b][1,3]oxazine. The corresponding reaction of arylpropynehydrazides with monosubstituted malonyl chlorides furnished pyrazolo[5,1‐b][1,3]oxazine‐7‐ones via intermediates that could not be isolated. The reaction of arylpropynehydrazides with monosubstituted malonyl chlorides leading to pyrazolo[5,1‐b][1,3]oxazines is reported. This method can also be extended to the synthesis of pyrazolidine‐3,5‐dione, which subsequently can be converted by thermolysis into a pyrazolo[5,1‐b][1,3]oxazine.