Tetrahedron p. 4967 - 4973 (2004)
Update date:2022-08-05
Topics:
Bianchi, Lara
Dell'Erba, Carlo
Maccagno, Massimo
Morganti, Stefano
Novi, Marino
Petrillo, Giovanni
Rizzato, Egon
Sancassan, Fernando
Severi, Elda
Spinelli, Domenico
Tavani, Cinzia
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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