Synthesis of six- to nine-membered ring oximinoorthodithiolactones by cyclization of nitroketene S,S-acetals in trifluoromethanesulfonic acid

2-Nitro-1,1-bis(phenylalkylthio)ethene or 1-(melhylthio)-2-nitro-1-(phenyla lkylthio)ethene derivatives tethered to an aromatic ring undergo a fast int ramolecular cyclization in trifluoromethanesulfonic acid, with the intermed iate formation of dications, which can be detected by NMR spectroscopy. Que nching with methanol at low temperature affords cyclic orthothioesters of i sothiochromanones, 4,5-dihydrobenzo[d]-thiepin-1-one, 5,6-dihydro-4H-benzo[ d]thiocin-1-one and 8,9,10,11-tetrahydro-7-thiabenzocyclononen-5-one oximes . The yields are usually fair to good, except for the nine-membered ring de rivatives.