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Polyphosphoric acid and N‐aryl‐N′‐benzoylethylenediamines in a type of Bischler‐Napieralski reaction afforded 1,2‐diaryl‐2‐imidazolines in good yields, rather than the 2,3‐dihydro‐1H‐[1,4]‐benzodiazepines. Blocking of the amino nitrogen by a methyl or ethyl group, to avoid imidazoline formation, gave starting material rather than the expected dihydrobenzodiazepine. When p‐tosyl was the blocking group, imidazoline was again the only product isolated. Analytical and spectroscopic data of several unreported 1,2‐diaryl‐2‐imidazolines are presented.

Reaction of 3‐oxo‐1,2‐benzoisothiazoline‐2‐acetic acid alkyl esters 1,1‐dioxide (1a‐d) with alkaline alkoxides was carried out under various conditions. Under mild conditions, o‐(N‐carboxymethylsulfamyl)benzoic acids dialkyl esters (2a‐d) were obtained with good yields. Reaction of 1a‐d or 2a‐d with sodium alkoxides under drastic conditions afforded 4‐hydroxy‐2H‐1,2‐benzothiazine‐3‐carboxylic acid alkyl esters 1,1‐dioxide (3a‐d). Transesterification was observed when esters 1b‐d were treated with sodium methoxide in methanol. Esters 3a‐d were hydrolyzed in concentrated aqueous sodium hydroxide affording the acid 6. Attempts to recrystallize 6 from water resulted in its decarboxylation to give 2H‐1,2‐benzothiazine‐4‐(3H)one 1,1‐dioxide (7). Compound 6 could not be obtained by acid hydrolysis of esters 3a‐d or by rearrangement of 3‐oxo‐1,2‐benzoisothiazoline‐2‐acetic acid 1,1‐dioxide (8). Different experimental evidence supports the suggestion that rearrangement took place by ethanolysis of the carboxamide linkage affording the open sulfonamides (fast step) followed by a Dieckmann cyclization (slow step). It was demonstrated that transesterification took place in the open sulfonamides 2.

Reaction of some 3‐oxo‐1,2‐benzoisothiazoline‐2‐acetamide 1,1‐dioxides (1a‐f) with alkaline alkoxides was carried out under various conditions. Under mild conditions, 1a‐f with sodium methoxide gave o‐(N‐carbox‐amidomethylsulfamyl)benzoic acid methyl esters (2a‐f, R = CH3). Compounds 1a or 2a reacted with sodium alkoxides under drastic conditions affording only ester 5. Under the same conditions, 1b‐d or 2b‐d gave 4‐hydroxy‐2H‐1,2‐benzothiazine‐3‐carboxamide 1,1‐dioxides (3b‐d), while 1e‐f or 2e‐f afforded the acid 6 in variable amounts, together with the expected benzothiazines 3e‐f. Isolation of ethyl ether as another product in the reaction of 1e‐f with sodium ethoxide supports the suggestion that the formation of 6 involves the O‐alkyl fission on the alkyl carbon of the esters 2e‐f. An explanation of these results may be related to the acidic character of the amide hydrogen in compounds 2e‐f.