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.