A convenient synthesis of the novel 5H-thieno[2,3-e]-4,1,2-oxathiazepine ring system via an alkoxycarbenium ion intermediate

3-(Methoxymethoxymethyl)-2-thiophenesulfonamides and 3-hydroxymethyl-N-methoxymethyl-2-thiophenesulfonamides have been shown to undergo cyclization when treated under anhydrous acidic conditions to provide the novel 2,3-dihydro-5H-thieno2,3-e]-4,1,2-oxathiazepine ring system. Incorporation of a primary sulfonamide group into position seven of the molecule provided compounds which inhibit human carbonic anhydrase II.