Symmetric allylic esters, alkylation

As described in the previous section, when acyclic and symmetric allylic esters such as l,3-diphenyl-2-propenyl acetate and l,3-dialkyl-2-propenyl esters are used as substrates, high to excellent enantioselective allylic alkylation is performed by using a variety of chiral ligands. In contrast, the number of successful examples of the asymmetric allylic alkylation of acyclic and unsymmetric allylic esters is relatively limited. 

The electrophile E+ can be an alkyl halide or sulfate, an aldehyde to give aldol products, or an a,P-unsatunited ester when conjugate addition is preferred. Examples from simple alkylation show that the alkyl halide can be primary alkyl, allylic 33, and even an a-bromoester or y-bromo-a,P-unsaturated ester 31. The original carbonyl compound that forms the chiral imine with SAMP or RAMP can be an aldehyde 27 or 29, a ketone (symmetrical 32 or blocked on one side 35), or an enone. Only the reagents and products are shown with oxidative [O] or hydrolytic [H20] workup. Notice that SAMP is used for the formation of either enantiomer of 28 by using different starting materials but that RAMP is used to enter the other enantiomeric series from 32. 

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