Enantioselectivity intramolecular carbopalladation

Based on a /rarcr-acetoxypalladation of the triple bond, Lu has developed a highly enantioselective (up to 87% ee) synthesis of 7-butyrolactones with Pd(n) catalysis (Scheme 73).280 Following the initial /ra/w-acetoxy-palladation, a plausible mechanism for this sequence involves an intramolecular carbopalladation of the pendant olefin, and deacetoxypalladation instead of the common /3-hydride elimination in the final step. 

A highly enantioselective intramolecular AHR of the cyclohexadienone 322 to give 324 with 96% ee in 100% conversion was carried out using the chiral phosphoamidite-type ligand (III-IO), which is monodentate. The stereogenic center was not created at the site of C—C bond formation, but instead the cyclohexadienone was desymmetrized. The use of Cy2MeN as a base gave the best result. It should be added that the carbopalladation product 323 has no jS-H syn to Pd, and hence the cyclized product 324 was formed by syn y3-H elimination after epimerization [132]. 

In 2007, Ln s group developed a cationic Pd(II)-catalyzed elegant carbopalladation of alkynoates 108 using arylboronic acids followed by enantioselective intramolecular addition to ketones of the resulting vinylpalladinm species [45] (Scheme 6.27). 

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