Allylic substitutions, functionalized Grignard

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-... 

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)]. 

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. 

The pyrrolinyl- (6-11) and pyrrolyl-substituted (12-13) eudistomin skeletons were first prepared by Rinehart from 1-cyano-P-carboline (145), which can be obtained from the corresponding acid (28). Grignard reaction with appropriately protected 3-bromopropanal (Scheme 4) provided the necessary carbons with appropriate oxidation level for cyclization to either of these ring systems. The pyrrolyl-substituted eudistomins then result upon hydrolysis of the imine and acetal functions with concomitant cyclization in the presence of ammonia. The pyrrolinyl-eudistomins require reduction of the imine to the amine followed by acetal hydrolysis and simultaneous ring closure to isomer 147. Reduction of the imine 147 followed by allylic oxidation with sodium hypochlorite isomerizes 147 to the pyrrolinyl-eudistomin skeleton (149). 

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