Sulfone, allyl phenyl 1,1 -dilithiated

Allylic sulfonyl carbanions react with electrophiles such as alkyl halides and aldehydes at the a-position. Although relatively strong bases like Bu"Li and LDA are usually used for deprotonation of allylic sulfur compounds, including sulfones, a catalytic two-phase system that consists of a concentrated aqueous NaOH solution and a quaternary ammonium salt can be used to generate allylic sulfonyl carbanions. 1,1-Dilithiated allyl phenyl sulfone (equation 20) reacts with excess benzaldehyde to afford the 1,3-( )-diadduct, while l,ort/io-dilithiated allyl phenyl sulfone gives the l,ort/io-diadduct predominantly. Other examples of sulfur-substituted allylic anions are summarized in Table 1. 

As shown in Scheme 3.21, treatment of ally phenyl sulfone with an excess of nBuLi affords a mixture of l,o-dilithiated allyl phenyl sulfone 109 and the 1,1-dUithiated compound 110 [78]. Quenching this mixture with benzaldehyde leads to a variety of products, including 112 and 113. However, it is interesting to note that, at 50 °C, the l,o-dilithiated species 109 is converted into the thermodynamically more stable 1,1-dUithiated allyl phenyl sulfone 110, which can undergo twofold reaction with benzaldehyde. This double lithiation coupling methodology has since been applied to various bis-electrophiles [79]. Competitive ortho-lithiation was al-... 

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