A novel synthetic approach to Pyrazolooxazines. One‐pot synthesis of Pyrazolo[5,1‐<i>c</i>][1,4]oxazine derivatives from 2,<scp>2‐dichlorovinylacetophenones</scp>

Abstract New convenient synthetic methods in pyrazoline and pyrazolooxazine chemistry have been developed starting from 2,2‐dichlorovinylacetophenones 4 , whose reaction with 2‐hydroxyethylhydrazine directly gave hitherto unknown 3‐aryl‐5‐dichloromethyl‐1‐(2‐hydroxiethyl)‐2‐pyrazolines 7 high yields. These were found to be able undergo cyclization afford 2‐aryl‐6,7‐dihydro‐4 H ‐pyrazolo[5,1‐ c ][1,4]oxazines 10 upon treatment sodium hydride. Compounds could also easily obtained near quantitative yields by a one‐pot preparative process involving of compounds followed addition hydroxide. The simplicity the yield this make it much more attractive than previously described multistep procedure. molecular structure 2‐(4‐chlorophenyl)‐6,7‐dihydro‐4 ][1,4]oxazine 10c was determined x‐ray crystallography.