The reaction between benzonitrile N-sulfide, generated from the fluoride ion catalyzed elimination of two molecules of hydrogen fluoride from (benzy1imino)sulfur difluoride, and either methyl propiolate or 3-butyn-%one gave predominantly the 4-substituted isothiazole isomer. Comparison of the isothiazole isomer ratios found for the Nsulfide generated from iminosulfur difluoride and phenyloxathiazolone leads to the conclusion that hydrogen fluoride causes an increased amount of 4-substituted isothiazole. Molecular orbital calculations (CND0/2) show that the interaction of the HOMO of the N-sulfide and the LUMO of the acetylenes gives the 4-substituted isothiazole. The observation that the 5-carbon absorbs significantly downfield from the 4-carbon in the NMR spectra of isothiazoles allows the unambiguous assignment of regiochemistry of the isothiazoles.

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Benzylamin (I) reagiert mit Schwefeltetrafluorid (II) zu (III), aus dem das Benzonitril‐ N‐sulfid (IV) erhalten wird, welches in Schwefel und Benzonitril (V) zerfällt.

Aus Benzyliminoschwefeldifluorid (I) erhält man in Gegenwart von Fluoridionen in situ das Benzonitrilsulfid (II), das mit den Acetylenen (III) zu Addukten (IV) führt.