2,1‐benzisothiazoles. XIII. Intermediates and products in the sulfur extrusion reaction of 2,1‐benzisothiazolin‐3(1<i>H</i>)‐one. A new synthesis of 11<i>H</i>‐pyrido[2,1‐<i>b</i>]quinazolin‐11‐one (“pyracridone”)

Abstract

Abstract Triethyl phosphite abstracts sulfur from 2,1‐benzisothiazolin‐3(1 H )‐one (1); a reaction intermediate is the spirocyclic compound 11 , and products include the benzoxazine 6 and polyanthraniloyl compounds. In the presence of pyridine, pyracridone ( 13 ) is formed. The ketene‐imine 9 is probably not an intermediate in these reactions. The reactions of other nucleophiles with 1 and with its N ‐methyl derivative 15 , have been examined.