| Abstract
| - The first efficient, one-pot method for methylenation of p-toluyl sulfones (i.e., the transformation ofp-MePhSO2CHR2 into R2CCH2) is described. Methods for effecting that transformation involving alkylationof sulfones with reagents of the general formula MCH2X, where M = SiMe3, SnR3, and MgCl (the Juliamethod) have been previously described. However, the silicon reagent is completely unreactive towardmany sulfones, the tin reagent typically affords only moderate yields, and the magnesium reagent typicallygives incomplete reaction (9−40% starting material). This article reports that excellent yields are obtainedby alkylating the sulfone with the more ionic lithium methylene carbenoids (LiCH2X, where X = Cl, Br,and I). For example, treatment of sulfone 1 with 3 equiv of n-BuLi (THF, −100 °C) followed by 2 equivof CH2Br2 affords olefin 2 in 96% yield. Although the carbenoid is generated in the presence of a 1:2mixture of α-lithio-sulfone and n-BuLi, it reacts selectively with the α-lithio-sulfone (Krel = 9.6 ± 0.8with LiCH2Br). The chlorocarbenoid LiCH2Cl reacts somewhat less selectively (Krel = 3.5). The alkyl-substituted carbenoid n-BuCHBrLi reacts ≥ 40 times more slowly than LiCH2Br, suggesting that olefinationoccurs by the SN2 mechanism rather than by metal-assisted ionization (MAI), the mechanism by whichcyclopropyl and vinylidene carbenoids react with nucleophiles. Finally, sulfones can be transformed intovinyl halides by treatment with 3 equiv of n-BuLi (THF, −78 °C), followed by >2 equiv ofdiisopropylamine, followed by 3 equiv of dihalomethane (CH2X2, where X2 = Cl2, BrCl, Br2, or I2). Allproducts are formed in high yield and purity.
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