Allylic substitutions, functionalized Grignard reagents

Backvall [47] studied the chemo- and regioselectivity of the substitution of allylic chlorides in the presence of allylic acetates by Grignard reagents in the presence of a catalytic amount of Li2CuCl4 and showed that the reaction was chemoselective (the acetate function remains unchanged), and the regioselectivity was in favor of the Sn2 product. In the cyclic compound, the reaction was also nr/-selective [Eq. (25)]. 

Initial studies on the application of these catalysts to allylic substitution reactions showed that the arenethiolate moiety functions as an excellent nontransferable group, and that the regioselectivity can be completely reversed by suitable changes in the reaction parameters [33]. If the reaction between geranyl acetate and n-BuM gl was carried out inTHFat—30°C with fast addition of the Grignard reagent to the reaction mixture, complete a selectivity was obtained. Raising the tempera-... 

Acetals as Chiral Auxiliaries. There have been many applications of acetals of 2,4-pentanediol as chiral auxiliaries to control the diastereoselectivity of reactions on another functional group. Examples include cyclopropanation of alkenyl dioxanes, lithium amide-mediated isomerization of epoxides to allylic alcohols, and addition of dioxane-substituted Grignard reagents or organolithiums to aldehydes. 

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