Enantioselective Functionalization of Prochiral Cyclobutanones and Cyclobutenones

Copper-Catalyzed Regio- and Stereoselective Three-Component Coupling of Allenyl Ethers with gem-Dichlorocyclobutenones and B2pin2

The three-component coupling method for regio- and stereoselective difunctionalization of allenes with allenyl ethers, bis(pinacolato)diboron, and gem-dichlorocyclobutenones as electrophiles was reported, yielding a variety of highly functionalized cyclobutenone products tethering with an alkenylborate fragment. The polysubstituted cyclobutenone products also underwent diverse transformations.

Rhodium-Catalyzed Asymmetric Arylation of Cyclobutenone Ketals

Complex cyclobutanes are important motifs in both bioactive molecules and natural products, yet their enantioselective preparation has not been widely explored. In this work, we describe rhodium-catalyzed enantioselective additions of aryl and vinyl boronic acids to cyclobutenone ketals. This transformation involves enantioselective carbometalation to give cyclobutyl-rhodium intermediates, followed by β-oxygen elimination to afford enantioenriched enol ethers. Overall, this addition serves as a surrogate for Rh-catalyzed 1,4-additions to cyclobutenone.

Synthesis of Cyclobutanones by Gold(I)-Catalyzed [2 + 2] Cycloaddition of Ynol Ethers with Alkenes

A broad scope synthesis of cyclobutanones by gold(I)-catalyzed [2 + 2] cycloaddition of ynol ethers with alkenes has been developed. We also found that internal aryl ynol ethers can undergo (4 + 2) cycloaddition reaction with alkenes leading to the corresponding chromanes.

Stereospecific Synthesis of Enantioenriched Alkylidenecyclobutanones via Formal Vinylidene Insertion into Cyclopropanone Equivalents

1-Sulfonylcyclopropanols are employed here as efficient cyclopropanone equivalents in a formal vinylidene insertion process, providing the first general synthetic route to enantioenriched alkylidenecyclobutanones. The addition of an alkenyl-Grignard reagent leads to an alkenylcyclopropanol capable of electrophilic activation by N-bromosuccinimide, triggering a regio- and stereospecific 1,2-migration and affording alkylidenecyclobutanones after elimination. Activation of the intermediate with other electrophiles such as HCl or mCPBA leads to the formation of various chiral cyclobutanones and γ-lactones via alternative pathways.

Catalytic enantioselective synthesis of benzocyclobutenols and cyclobutanols via a sequential reduction/C-H functionalization

We report here a sequential enantioselective reduction/C-H functionalization to install contiguous stereogenic carbon centers of benzocyclobutenols and cyclobutanols. This strategy features a practical enantioselective reduction of a ketone and a diastereospecific iridium-catalyzed C-H silylation. Further transformations have been explored, including controllable regioselective ring-opening reactions. In addition, this strategy has been utilized for the synthesis of three natural products, phyllostoxin (proposed structure), grandisol and fragranol.