Oximes trifluoromethanesulfonic acid

Cyclization of the sulfides 547 under Friedel-Crafts conditions affords the 4-oxo-l //-2-bcnzothiopyran-l -carboxy-lates (Scheme 229) <1996JOM(507)215, 1999JME751> and treatment of l,l-bis(benzylthio)-2-nitroethene with trifluoromethanesulfonic acid generates a dication which affords the isothiochroman-4-one oxime 548 upon quenching with MeOH (Scheme 230) <2001EJ01525>. 

Nitroacetanilides, obtained by alkaline hydrolysis of l-arylamino-l-methylthio-2-nitroethenes, are readily cyclised to isatin-3-oximes by the use of concentrated sulfuric acid or trifluoromethanesulfonic acid at room temperature the latter giving somewhat higher yields. Although this methodology is related to the Sandmeyer methodology, it has no obvious benefit over the latter (Scheme 7). 

Isothiochroman-4-one oxime 41 results from quenching the dication generated in a solution of l-(benzylthio)-l-(methylthio)-2-nitroethene in trifluoromethanesulfonic acid with methanol (Scheme 46) <01EJO1525>. 

Phosphorous pentoxide effectively catalyzed the homogeneous liquid phase Beckmann rearrangement of cyclohexanone oxime 5 to lactam 6 in DMF. The catalytic activity was significantly increased by addition of trifluoromethanesulfonic acid as a co-catalyst. This protocol was fiuther extended to the rearrangement of acetone, acetophenone and cyclopentanone oxime to the corresponding amides. 

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