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Cycloaddition of 2H-Pyran-2-thiones with Nitroso Derivatives. An Unexpected Cycloaddition-Rearrangement Reaction

✍ Scribed by Albert Defoin; Gérard Augelmann; Hans Fritz; Guillaume Geffroy; Christian Schmidlin; Jacques Streith

Publisher
John Wiley and Sons
Year
1985
Tongue
German
Weight
961 KB
Volume
68
Category
Article
ISSN
0018-019X

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✦ Synopsis

Reaction of pyran-2-thiones 4 with nitroso derivatives led surprisingly to type-8 (19) adducts which proved to be isomeric with the initially expected primary Diels-Alder cycloadducts 5. Methyl 2-thioxo-2H-pyran-5-carboxylate (40, when reacted with nitrosobenzene at -lo", led quantitatively to the thieto-oxazine intermediate 13, which turned out to be the cornerstone of the complex cycloaddition-rearrangement 5 4 reaction pathway (Scheme 3 ) . Differential scanning calorimetry, as performed for the 18a-19a conversion, permitted to demonstrate that this multistep rearrangement is overall a highly exothermal process, the final product 19 representing an energy-sink along this reaction pathway.

Introduction. ~ In [l]

, we have described a simple three-step synthesis of some racemic diamino-sugars 3, starting from 1,2-dihydropyridines and from nitrosobenzene. During the first reaction step, Diels-Alder cycloaddition led regiospecifically to the bicyclic products 1 which were oxidized to the glycols 2 and then hydrogenolyzed to the expected racemic diamino-sugars 3.

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