Benzisothiazoles and their 1,1 -Dioxides

Benzisothiazoles suffer straightforward ring cleavage, but their 1,1-dioxides, 2,1-benzisothiazoles and derivatives of saccharin give products containing no sulfur. 

Isothiazole and the benzisothiazoles are planar molecules, and the 1,1-dioxides, saccharin and thiosaccharin, and their salts, are all planar, apart, of course, from the oxygen atoms on sulfur. Calculations on isothiazole-1-oxide show that the heterocyclic ring has an envelope conformation, with the sulfur atom 22 pm above, and the oxygen atom 85 pm below, the plane of the other four atoms of the ring. This, of course, would result in a significant dipole moment, calculated to be 1.27 D, perpendicular to the plane of the ring <92JP074>. 

We venture to make an assignment of aromatic proton signals in phenylene fragment and have found that the changeover from 1,2-benzisothiazoles to their oxides and dioxides involves an increase of the chemical shift values H-7. 

General features of the conformations of isothiazole derivatives were discussed in CHEC-II(1996) <1996CHEC-11(3)319>. Isothiazole and the benzisothiazoles are planar molecules, as are the corresponding A,A-dioxides, saccharin, thiosaccharin, and their salts. 1,2-Benzisothiazoline A,A-dioxide in the crystalline state exists as a 1 1 mixture of two conformers. 

In view of their importance in enantioselective reactions, many bornane sultams have been synthesized and characterized by MS. Their El mass spectra show molecular ions with low abundance or are absent. N-Substituted bornane sultams generally show the typical fragmentations of the substituents <2000THS(4)405>. 1-Alkyl-7-nitro-2,1-benzisothiazole 2,2-dioxides show elimination of an acyl radical from their molecular ions <1997EJS55>. 

Few examples of functionalization on the benzene ring of benzisothiazole have been reported (see Section 4.05.7.2). Studies on the reactivity of unsaturated chains in cycloaddition reactions have been reported (see Section 4.05.7.3). The high reactivity of 4-vinylisothiazolin-3-one A-oxides in Diels-Alder cycloadditions, both as diene and dienophile, is illustrated by their tendency to dimerize. 5-Vinylisothiazole A,A-dioxides react at the vinyl function with different 1,3-dipoles. Isothiazolo-3-sulfolenes 265 give an o-quinodimethane which can be trapped with a dienophile. Different isothiazole derivatives substituted with a carbon chain functionalized with heteroatoms have been prepared as ligands for the formation of complexes. 3-Oxocamphorsulfonimide reacts with the anion of alkynes and several studies on the reactivity of the products with electrophiles are reported. 

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