The chemoselective addition of arenes and 1,3-diketones to α-aryldiazoesters was achieved through ligand-controlled gold catalysis. Unlike a dirhodium catalyst (which promotes C(sp3)-H insertion and cyclopropanation) and a copper catalyst (which catalyzes O-H and N-H insertions), the gold catalyst with an electron-deficient phosphite as the ancillary ligand exclusively gave the carbophilic addition product, thus representing a new and efficient approach to form "carbophilic carbocations", which selectively react with carbon nucleophiles.
Phosphine-catalyzed regiodivergent enantioselective C-2- and C-4-selective γ-additions of oxazolones to 2,3-butadienoates have been developed. The C-4-selective γ-addition of oxazolones occurred in a highly enantioselective manner when 2-aryl-4-alkyloxazol-5-(4H)-ones were employed as pronucleophiles. With the employment of 2-alkyl-4-aryloxazol-5-(4H)-ones as the donor, C-2-selective γ-addition of oxazolones took place in a highly enantioselective manner. The C-4-selective adducts provided rapid access to optically enriched α,α-disubstituted α-amino acid derivatives, and the C-2-selective products led to facile synthesis of chiral N,O-acetals and γ-lactols. Theoretical studies via DFT calculations suggested that the origin of the observed regioselectivity was due to the distortion energy that resulted from the interaction between the nucleophilic oxazolide and the electrophilic phosphonium intermediate.
The first enantioselective formal [5+4] cycloaddition is realized under palladium catalysis to deliver benzofuran-fused nine-membered rings. These medium-sized heterocycles and derivatives undergo unique rearrangements induced by transannular bond formation, resulting in the production of two classes of densely substituted polycyclic heterocycles in excellent efficiency and stereoselectivity.
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