Easy access to 4-nitrothiochroman S, S-dioxides via ring-enlargement from 3-nitrobenzo[ b]thiophene
The ( E)-2-aryl-1-[2-(methylthio)phenyl]-1-nitroethylenes 5 can easily be oxidized to the relevant sulfones 6 and effectively subjected to cyclization via an intramolecular Michael addition after metallation with lithium bis(trimethylsilyl)amide in THF. After quenching with ammonium chloride the 3-a...
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Published in | Tetrahedron Vol. 60; no. 23; pp. 4967 - 4973 |
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Main Authors | , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
OXFORD
Elsevier Ltd
31.05.2004
Elsevier |
Subjects | |
Online Access | Get full text |
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Summary: | The (
E)-2-aryl-1-[2-(methylthio)phenyl]-1-nitroethylenes
5
can easily be oxidized to the relevant sulfones
6
and effectively subjected to cyclization via an intramolecular Michael addition after metallation with lithium bis(trimethylsilyl)amide in THF. After quenching with ammonium chloride the 3-aryl-4-nitrothiochroman
S,
S-dioxides
2
are obtained as diastereomeric mixtures in good to excellent yields. Both yields and stereochemistry of the ring-closure step appear to be influenced by steric effects of the 3-aryl moiety. As sulfides
5
derive from an initial ring opening of 3-nitrobenzo[
b]thiophene (
1
), the overall
1
to
2
process can be considered as an effective 5 to 6 ring enlargement of the sulfur heterocycle. A conformational
1H NMR and molecular-mechanics investigation on the isolated diastereomeric
2
has also been accomplished.
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ISSN: | 0040-4020 1464-5416 |
DOI: | 10.1016/j.tet.2004.04.039 |