Dong M, Qi L, Qian J, Yu S, Tong X. Pd(0)-Catalyzed Asymmetric 7-
Endo Hydroacyloxylative Cyclization of 1,6-Enyne Enabled by an Anion Ligand-Directed Strategy.
J Am Chem Soc 2023;
145:1973-1981. [PMID:
36638241 DOI:
10.1021/jacs.2c12756]
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Abstract
Despite diversity in reaction mechanisms, the palladium-catalyzed cyclization of 1,6-enyne generally proceeds in a 5-exo manner. Herein, we report the development of a Pd(0)-catalyzed hydroacyloxylative cyclization of 1,6-enyne in either 7-endo-trig or 6-exo-trig fashion when paired with an appropriate dihaloacetic acid reactant, such as F2HCCO2H and Cl2HCCO2H. Using the combination of Pd2(dba)3 and a chiral phosphine ligand, the hydroacyloxylative cyclization of 1,6-enyne bearing a 1,1-disubstituted alkene moiety readily gives highly enantiopure seven-membered heterocycles while the reaction of those having a 1,2-disubstituted alkene affords six-membered rings with moderate enantioselectivity. Preliminary experimental studies suggest a reaction mechanism featuring an unusual E-to-Z vinyl-Pd(II) isomerization and alkene trans-oxypalladation, which is proven to be governed by the rationally selected carboxylate.
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