Cycloaddition-elimination reactions of 4-methyl-5-(substituted)-imino-Δ2-1,2,3,4-thiatriazolines with isocyanates |
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Authors: | Gerrit L'abb ,Nancy Weyns,Ingrid Sannen,Pieter Delbeke,Suzanne Toppet |
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Affiliation: | Gerrit L'abbé,Nancy Weyns,Ingrid Sannen,Pieter Delbeke,Suzanne Toppet |
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Abstract: | 4-Methyl-5-(substituted)imino-1,2,3,4-thiatriazolines 1 (R2 ≠ Me) undergo cycloaddition-elimination reactions with isocyanates to yield 4-methyl-5-(substituted)imino-1,2,4-thiadiazolidine-3-ones 5 via the thermodynamically less stable isomers 4 . The latter have not been isolated, except for 4q which was shown to iso-merize rapidly into 5q with phenylsulfonyl isocyanate. The reactions of 1 are accelerated by using less bulky R2 substituents and more electrophilic isocyanates, in accordance with the viewpoint that 1 reacts as a masked 1,3-dipole. The products 4i-n (= 5i-n ), derived from 1b , add isocyanates reversibly to give 2,3,4,5-tetrahydro-6aλ4-thia-1,3,4,6-tetraazapentalene-2,5-diones 9i-n , which have been isolated and characterized spectroscopically. Such compounds with a hypervalent sulfur atom thus occur as intermediates during the isomerization of 4 to 5 under the influence of isocyanates. |
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