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 can easily be oxidized to the relevant sulfones 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 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 derive from an initial ring opening of 3-nitrobenzo[b]thiophene (), the overall to 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 has also been accomplished.