Elimination leaving groups

When the anions of these acids are good leaving groups, elimination from their enol esters can be readily induced by comparatively weak bases. This is the case for p-bromobenzenesulphonates and triflates. Thus decarboxylative elimination from enol sulphonates 28 furnishes good yields of 2-alkynoic acids (equation 88), when R... 

Substitution —trade a nucleophile for a leaving group Elimination—lose a leaving group and usually a proton to form a pi bond Addition —add a nucleophile or electrophile or both to a pi bond Rearrangement—produce a constitutional isomer... 

The benzylation of both activated and deactivated arenes has been achieved using the boron trifluoride activation of A -methyl hydroxamate leaving groups to liberate the reactive benzyl cations. Elimination of p-toluenesulfinic acid from a-amidosulfones under the influence of tris(pentafluorophenyl)borane gives acyl iminium ions, which may attack activated arenes to yield p-tolylsulfone derivatives (12), as indicated in Scheme 1 (where Cbz represents the fV-benzyloxycarbonyl leaving group). Elimination... 

Most of the new reactions in this chapter are examples of addition-elimination processes. This mechanism has appeared occasionally before, but it is emphasized in this chapter for the first time. Any carbonyl compound bearing a leaving group can be attacked by a nucleophile to give a tetrahedral intermediate (addition) that can then expel the leaving group (elimination) (Fig. 17.66). 

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