A ring enlargement from seven- to ten-membered-ring sulfonamide derivatives

Abstract

The reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine (1a) with 4,S-dihydro-7,8-dimethoxy-l,2-benzothiazepin-3-one 1,1-dioxide (4) in dioxane at room temperature gave the correspondingly substituted 4H-1,2,5- benzothiadiazecin-6-one 1,1-dioxide 5a in 64% yield (Scheme 2). The structure of this novel ten-membered ring-enlargement product was established by X-ray crystallography (Fig.). Under more vigorous conditions (refluxing dichloroethane), 5a was formed together with the isomeric 6a, both in low yield. The 3-(dimethylamino)-2H-azirines 1b and 1c reacted sluggishly to give the two isomeric ring-enlargement products of type 5 and 6 in yields of 24-29 % and 2-4 % , respectively (Table 1 ). Even less reactive is 2,2-dimethyl-3-(N-methyl-N-phenylamino)-2H-azirine (1d), which reacted with 4 in MeCN only at 65°. Under these conditions, besides numerous decomposition products, only traces of 5d and 6d were formed. No ring enlargement was observed with the sterically crowded 1e, which bears an isopropyl group at C(2).