Regio‐ and stereoselective synthesis of spiro[1‐benzothiepine‐4(5 h ), 3′(3 h )‐pyrazol]‐5‐ones

Reaction of (4 E )‐4‐arylmethylene‐3,4‐dihydro‐1‐benzothiepin‐5(2 H )‐ones 3a‐e with nitrilimines (generated in situ via triethylamine dehydrohalogenation of the corresponding hydrazonoyl chlorides 4a, b ) in refluxing benzene, afforded 2′,4′,5′‐triaryl‐2,2′,3,4′‐tetrahydro‐spiro[1‐benzothiepine‐4(5 H ),3′(3 H )‐pyrazol]‐5‐ones 5a‐i and not the isomeric forms spiro[1‐benzothiepine‐4(5 H ),4′(4 H )‐pyrazol]‐5‐ones 6 in high regioselective manner. Single crystal X‐ray diffraction studies of 5a, f, g indicated that the isolated products are 3′ R , 4′ S.