Tandem Nitroaldol−Dehydration Reactions Employing the Dianion of Phenylsulfonylnitromethane1

Reaction of phenylsulfonylnitromethane (1) with more than 2 molar equiv of LDA afforded the dilithium salt of phenylsulfonylnitromethane. Condensation of this dilithium salt with unbranched aldehydes occurred readily, but the initial nitroaldols dehydrated to afford unconjugated β,γ-unsaturated α-nitrosulfones in 52−88% yield. Evidence is presented that the β,γ-unsaturated α-nitrosulfones can equilibrate with the conjugated α,β-unsaturated α-nitrosulfones at neutral pH. The normally disfavored α,β-unsaturated α-nitrosulfones have been implicated in the formation of bis(α-nitrosulfones), Michael adducts of phenylsulfonylnitromethane. Three diastereomers (1R,2s,3S, 1R,2r,3S, and 1R,3R/1S,3S) have been identified for the bis(α-nitrosulfones) obtained in these reactions. In the case of acetaldehyde, condensation with the dilithium salt of phenylsulfonylnitromethane afforded only bis(α-nitrosulfones). The main product (three diastereomers) was the bis(α-nitrosulfone) derived from Michael addition of phenylsulf...