Ligand-induced acceleration of the intramolecular [3 + 2] cycloaddition between alkynes and alkylidenecyclopropanes

Palladium-Catalyzed Nucleophilic Reaction of Alkylidenecyclopropanes with β,γ-Unsaturated α-Ketoesters: Ligand-Controlled Divergent Synthesis

A palladium-catalyzed ligand-controlled selective 1,4-addition and cycloaddition reaction of β,γ-unsaturated α-ketoesters with alkylidenecyclopropanes (ACPs) has been developed. Using ACPs and β,γ-unsaturated α-ketoesters as starting materials, γ-dienyl-α-ketoesters and dihydro-2H-pyrans could be prepared selectively by modulating the ligand. A range of multisubstituted α-ketoesters and dihydro-2H-pyrans were obtained in moderate to excellent yields with excellent regioselectivities.

Co-Catalyzed Asymmetric Intramolecular [3+2] Cycloaddition of Yne-Alkylidenecyclopropanes and its Reaction Mechanism

Developing new transition metal-catalyzed asymmetric cycloadditions for the synthesis of five-membered carbocycles (FMCs) is a research frontier in reaction development due to the ubiquitous presence of chiral FMCs in various functional molecules. Reported here is our discovery of a highly enantioselective intramolecular [3+2] cycloaddition of yne-alkylidenecyclopropanes (yne-ACPs) to bicyclo[3.3.0]octadiene and bicyclo[4.3.0]nonadiene molecules using a cheap Co catalyst and commercially available chiral ligand (S)-Xyl-BINAP. This reaction avoids the use of precious Pd and Rh catalysts, which are usually the choices for [3+2] reactions with ACPs. The enantiomeric excess in the present reaction can be up to 92 %. Cationic cobalt(I) species was suggested by experiments as the catalytic species. DFT calculations showed that this [3+2] reaction starts with oxidative cyclometallation of alkyne and ACP, followed by ring opening of the cyclopropyl (CP) group and reductive elimination to form the cycloadduct. This mechanism is different from previous [3+2] reactions of ACPs, which usually start from CP cleavage, not from oxidative cyclization.

DBU-catalyzed [3 + 2] cycloaddition and Michael addition reactions of 3-benzylidene succinimides with 3-ylidene oxindoles and chalcones

A metal-free DBU catalyzed protocol has been developed for the regioselective [3 + 2] cycloaddition reactions of 3-benzylidene succinimides with 3-ylidene oxindoles to furnish spirooxindole derivatives. The 3-benzylidene succinimides underwent Michael addition with chalcones to provide benzylidene succinimide-tethered propanones. All the reactions proceeded under mild conditions and the products were isolated by simple filtration and washing with ethanol in good yields. The current methodology utilizes simple precursors and provides functionally-rich succinimides with two to five contiguous stereocenters in excellent diastereoselectivity and with complete regioselectivity.

Recent Methodologies That Exploit C-C Single-Bond Cleavage of Strained Ring Systems by Transition Metal Complexes

In this review, synthetic and mechanistic aspects of key methodologies that exploit C-C single-bond cleavage of strained ring systems are highlighted. The focus is on transition-metal-catalyzed processes that are triggered by C-C bond activation and β-carbon elimination, with the review concentrating on developments from mid-2009 to mid-2016.

Transition metal mediated carbonylative benzannulations

This review summarizes novel building blocks recently developed for transition metal-catalyzed carbonylative benzannulations.

Recent advances in the chemical transformations of functionalized alkylidenecyclopropanes (FACPs)

Classification of functionalized alkylidenecyclopropanes (FACPs) and recent chemical transformations for the synthesis of novel and useful polycyclic and heterocyclic compounds.

Nickel-catalyzed intramolecular [3 + 2 + 2] cycloadditions of alkylidenecyclopropanes. A straightforward entry to fused 6,7,5-tricyclic systems

A highly diastereo- and chemoselective intramolecular nickel-catalyzed cycloaddition of alkene- and alkyne-tethered alkynylidenecyclopropanes is reported. The method constitutes the first fully intramolecular [3 + 2 + 2] alkylidenecyclopropropane cycloaddition occurring via a proximal cleavage of the cyclopropane and makes it possible to build relevant 6,7,5-tricyclic frameworks in a single-pot reaction. Importantly, the reaction outcome is highly dependent on the characteristics of the nickel ligands.

Stereospecific synthesis of alkylidenecyclopropanes via sequential cyclopropene carbomagnesation/1,3-carbon shift

Alkylidenecyclopropanes can be synthesized from enantiomerically enriched cyclopropene derivatives with >99% stereotransfer and good to excellent yield. The protocol comprises the stereoselective reaction of Grignard reagents with 1-alkoxymethyl-3-hydroxymethylcyclopropenes and a stereospecific [1,3] carbon shift reaction.

Phosphoramidites: privileged ligands in asymmetric catalysis

Asymmetric catalysis with transition-metal complexes is the basis for a vast array of stereoselective transformations and has changed the face of modern synthetic chemistry. Key to this success has been the design of chiral ligands to control the regio-, diastereo-, and enantioselectivity. Phosphoramidites have emerged as a highly versatile and readily accessible class of chiral ligands. Their modular structure enables the formation of ligand libraries and easy fine-tuning for a specific catalytic reaction. Phosphoramidites frequently show exceptional levels of stereocontrol, and their monodentate nature is essential in combinatorial catalysis, where a ligand-mixture approach is used. In this Review, recent developments in asymmetric catalysis with phosphoramidites used as ligands are discussed, with a focus on the formation of carbon-carbon and carbon-heteroatom bonds.

γ-Methylidene-δ-valerolactones as a coupling partner for cycloaddition: Palladium-catalyzed [4+3] cycloaddition with nitrones

A new type of reagent, γ-methylidene-δ-valerolactones, has been devised, which acts as a four-carbon unit in a Pd-catalyzed cycloaddition reaction through the formation of a 1,4-zwitterionic species. The utility has been demonstrated in the context of stereoselective [4+3] cycloaddition with nitrones to provide highly functionalized 1,2-oxazepines, including the asymmetric variant with high enantioselectivity.