Copper-Catalyzed Ring-Opening/Borylation of Cyclopropenes

Since organoboron compounds readily undergo a diverse array of transformations and are widely used in various fields,the development of C-B-bondforming reactions have attracted considerable attention.Herein,we report a new method for forming C-B bonds by means of Cu-catalyzed ring-opening/borylation reactions of cyclopropenes.This method provides efficient access to a new type of stable allylborane-Lewis base adduct,which is a versatile synthon.The configuration of the products can be well controlled with this method,and some of the configurations we obtained are inaccessible by other catalytic methods for generating allylborons.Mechanistic studies indicated that the reactions proceed via insertion of an alkenyl Cu carbene—generated in situ by cyclopropene ring opening—into the B-H bond;the ring-opening step determines both the rate and stereochemistry.

Dinuclear gold-catalyzed C–H bond functionalization of cyclopropenes

We report an unprecedented C-H bond functionalization of cyclopropenes enabled by dinuclear gold catalysis.Highly selective C-H allylation,alkynylation and halogenation of cyclopropenes with organic halides have been realized.The reaction does not require strong external oxidants and affords access to functionalized cyclopropenes in moderate to good yields.The reductive elimination process to controllably construct C-C or C-X bonds can be tuned by using different dinuclear gold catalysts.

Ring-opening metathesis polymerization of cyclopropene derivatives towards polyolefin elastomer analogues

Polyolefin elastomers(POEs) are important reprocessable industrial materials with high strain-recovery performance. Traditional POEs are prepared from transition-metal-catalyzed polymerization of ethylene and α-olefins, while because of the complicated coordination polymerization mechanism, defining the actual distribution and length of alkyl branches in POEs is extremely challenging. We herein propose an alternative approach of synthesizing POE analogues from ring-opening metathesis polymerization(ROMP) of highly strained 3,3-alkyl-substituted cyclopropenes(CPEs). The structures of monomers and the substituents of Ru-catalysts are investigated in detail to evaluate the homobenzyl-substituted CPE derivative as a new living ROMP monomer. After copolymerization with cyclooctene and backbone hydrogenation, POE analogues with well-defined alkyl branches are prepared. Since the ROMP reactions have little isomerization and can also give good control of molecular weight and copolymer composition, it is hypothesized that this synthetic approach provides a novel platform to assist understanding the influence of branches on the properties of POEs.

Controlled semi-Pinacol rearrangement on a strained ring:Efficient access to multi-substituted cyclopropanes by group migration strategy

We describe a versatile electrophile addition/SPR sequence of readily available cyclopropyl carbinols that affords multi-substituted carbonylated cyclopropanes with high stereo-fidelity.This approach tolerates various heteroatom electrophiles,migration of carbon moiety of all possible hybridization states,facile ring reorganization and natural compound valorization.The examples represent an unprecedented version of SPR wherein migration to a non-benzylic bulky tertiary carbo-cation is realized with promising enantiocontrol.

Highly Enantioselective Trapping of Carboxylic Oxonium Ylides with Imines for Direct Assembly of Enantioenriched γ-Butenolides

Enantioenrichedγ-butenolides are valuable structural cores in many pharmaceuticals and natural products,but their direct and catalytically asymmetric assembly remains rare.Here,we report an efficient,atom-economic synthetic strategy for enantioenrichedγ-butenolides via a unique enantioselective reaction of cyclopropene carboxylic acids with imines under the synergistic catalysis of Rh2(esp)2/chiral Brønsted acid system.The reaction involved trapping of carboxylic oxonium ylides,generated from cyclopropene carboxylic acids,which presented as the first asymmetric trapping reactive intermediate in the process.

Blue light-promoted cyclopropenizations of N-tosylhydrazones in water

Carbene transfer reactions play an important role in the field of organic synthesis because of their ability to construct a variety of molecules. Herein, we reported on blue light-induced cyclopropenizations of N-tosylhydrazones in water, which avoids the use of expensive metal-based catalysts and toxic organic solvents. This metal-free and operationally simple methodology enable highly efficient cyclopropenizations, X-H insertion reactions, and cyclopropanation under mild reaction conditions.