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Cycloaddition of 2 H ‐Pyran‐2‐thiones with Nitroso Derivatives. An Unexpected Cycloaddition‐Rearrangement Reaction
Author(s) -
Defoin Albert,
Augelmann Gérard,
Fritz Hans,
Geffroy Guillaume,
Schmidlin Christian,
Streith Jacques
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680724
Subject(s) - chemistry , cycloaddition , nitrosobenzene , adduct , nitroso , pyran , rearrangement reaction , medicinal chemistry , photochemistry , cope rearrangement , organic chemistry , catalysis
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‐2 H ‐pyran‐5‐carboxylate ( 4f ), when reacted with nitrosobenzene at ‐10°, led quantitatively to the thieto‐oxazine intermediate 13 , which turned out to be the cornerstone of the complex cycloaddition‐rearrangement 5 → 8 reaction pathway ( Scheme 3 ). Differential scanning calorimetry, as performed for the 18a → 19a conversion, permitted to demonstrate that this multistep rearrangement is overall a higly exothermal process, the final product 19 representing an energy‐sink along this reaction pathway.