Catalytic Enantioselective Synthesis of Highly Functionalized Difluoromethylated Cyclopropanes

The first catalytic asymmetric synthesis of highly functionalized difluoromethylated cyclopropanes is described. The method, based on a rhodium‐catalyzed cyclopropanation of difluoromethylated olefins, gives access to a broad range of cyclopropanes bearing ester, ketone, or nitro functional groups. By using Rh₂((S )‐BTPCP)₄ as a catalyst, the corresponding products were obtained in high yields and high diastereo‐ and enantioselectivities (up 20:1 d.r. and 99 % ee ). This methodology allowed preparation of enantioenriched difluoromethylcyclopropanes for the first time.     

Copper(I)‐Catalyzed Chemoselective Coupling of Cyclopropanols with Diazoesters: Ring‐Opening C−C Bond Formations

Reported herein is an exceptional chemoselective ring‐opening/C(sp³)−C(sp³) bond formation in the copper(I)‐catalyzed reaction of cyclopropanols with diazo esters. The conventional O−H insertion product is essentially suppressed by judicious choice of reaction conditions. DFT calculations provide insights into the reaction mechanism and the rationale for this unusual chemoselectivity.     

Copper‐Catalyzed Enantio‐, Diastereo‐, and Regioselective [2,3]‐Rearrangements of Iodonium Ylides

The first highly enantioselective, diastereoselective, and regioselective [2,3]‐rearrangement of iodonium ylides has been developed as a general solution to catalytic onium ylide rearrangements. In the presence of a chiral copper catalyst, substituted allylic iodides couple with α‐diazoesters to generate metal‐coordinated iodonium ylides, which undergo [2,3]‐rearrangements with high selectivities (up to >95:5 r.r., up to >95:5 d.r., and up to 97 % ee ). The enantioenriched iodoester products can be converted stereospecifically into a variety of onium ylide rearrangement products, as well as compounds that are not accessible by classical onium ylide rearrangements.     

Malonic Acid Diazoesters for C−H Insertion Crosslinking (CHic) Reactions: A Versatile Method for the Generation of Tailor‐Made Surfaces

A simple and versatile method for the modification of a broad spectrum of surfaces with thin polymer films through the thermally or photochemically induced generation of surface‐attached polymer networks is reported. The system is based on copolymers containing diazomalonate groups, which can be activated by heat or light. To this end, the copolymers are deposited from solution onto solid substrates by standard techniques of thin‐film deposition (spin coating, dip coating). Upon activation the diazomalonate group decomposes and forms a carbene, which induces C−H insertion crosslinking (CHic) reactions. In the course of this process network formation and covalent surface attachment occur at the same time. The crosslinking process proceeds very rapidly, especially when the carbenes generated in the activation process cannot undergo Wolff‐rearrangement. The presented system can be used for the generation of a wide range of polymer layers and microstructures on a broad spectrum of surfaces.     

Catalytic Divergent [3+3]‐ and [3+2]‐Cycloaddition by Discrimination Between Diazo Compounds

Highly selective divergent cycloaddition reactions of enoldiazo compounds and α‐diazocarboximides catalyzed by copper(I) or dirhodium(II) have been developed. With tetrakis(acetonitrile)copper(I) tetrafluoroborate as the catalyst epoxypyrrolo[1,2‐a]azepine derivatives were prepared in good yields and excellent diastereoselectivities through the first reported [3+3]‐cycloaddition of a carbonyl ylide. Use of Rh₂(pfb)₄ or Rh₂(esp)₂ directs the reactants to regioselective [3+2]‐cycloaddition generating cyclopenta[2,3]pyrrolo[2,1‐b]oxazoles with good yields and excellent diastereoselectivities.