Benzisoxazolium salts

Extensive UV absorption data (as well as NMR and IR data) have been reported for a large number of 2,1-benzisoxazolium salts. The salts show three absorption maxima at 270-273, 280 and 335-338 nm (73DIS(B)1434, 71JOC1543). 

The IR (and Raman) spectra of 1,2-benzisoxazole and 2,1-benzisoxazole have been recorded and their fundamental and combined vibrations assigned (80MI41604). Similar studies have been carried out with 2,1-benzisoxazolium salts (74DIS(B)147, 71JOC1543). 

The photodecomposition of 2,1-benzisoxazolium salts gave iV-substituted phenones (Scheme 22). In one case the l-(adamantyl)-3-phenyl-2,l-benzisoxazolium cation (51) did not generate a substituted phenone with reductive ring substitution. Rather, adamantyl ring rupture occurred to produce (52) (Scheme 22) (78JOC123.3, 77JOC3929). 

The 2,1-benzisoxazolium salts unsubstituted in the 3-position behave in an analogous manner to their 1,2-isomers above. Particularly interesting is the reaction of the salt (134) with EtaN. Abstraction of the C(3)-proton is followed by ring opening to the iminoketene (135) which undergoes electrocyclization to its stable valence tautomer (136) in 84% yield (71JA1543). 

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