Easy access to 4-nitrothiochroman S, S-dioxides via ring-enlargement from 3-nitrobenzo[ b]thiophene

• Published in: Tetrahedron Vol. 60; no. 23; pp. 4967 - 4973
• Main Authors: Bianchi, Lara, Dell'Erba, Carlo, Maccagno, Massimo, Morganti, Stefano, Novi, Marino, Petrillo, Giovanni, Rizzato, Egon, Sancassan, Fernando, Severi, Elda, Spinelli, Domenico, Tavani, Cinzia
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 31.05.2004; Elsevier
• Subjects: 3-Nitrobenzo[ b]thiophene; Chemistry; Chemistry, Organic; Conformations; Nitrothiophenes; Physical Sciences; Ring enlargement; Ring-opening/ring-closure reactions; Science & Technology; Thiochromans; Conformations; 3-Nitrobenzo[ b]thiophene; Ring-opening/ring-closure reactions; Ring enlargement; Nitrothiophenes; Thiochromans; MAGNETIC RESONANCE SPECTRA; THIOCHROMANS; ANALOGS; DERIVATIVES; INTRAMOLECULAR CYCLOADDITION; STEREOCHEMISTRY
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2004.04.039

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. Graphic