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Cycloaddition‐elimination reactions of 4‐methyl‐5‐(substituted)‐imino‐Δ 2 ‐1,2,3,4‐thiatriazolines with isocyanates
Author(s) -
L'abbé Gerrit,
Weyns Nancy,
Sannen Ingrid,
Delbeke Pieter,
Toppet Suzanne
Publication year - 1991
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570280238
Subject(s) - chemistry , isocyanate , cycloaddition , isomerization , hypervalent molecule , electrophile , yield (engineering) , medicinal chemistry , sulfur , phenylisocyanate , organic chemistry , catalysis , reagent , materials science , metallurgy , polyurethane
4‐Methyl‐5‐(substituted)imino‐1,2,3,4‐thiatriazolines 1 (R 2 ≠ 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 R 2 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‐6aλ 4 ‐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.