Nickel-Catalyzed Intermolecular [3+2+2] and [2+2+2] Cocyclizations of Bicyclopropylidene and Alkynes

Cobalt(I)-Catalyzed (3 + 2 + 2) Cycloaddition between Alkylidenecyclopropanes, Alkynes, and Alkenes

Cobalt(I) catalysts equipped with bisphosphine ligands can be used to promote formal (3 + 2 + 2) intramolecular cycloadditions of enynylidenecyclopropanes of type 1. The method provides synthetically appealing 5,7,5-fused tricyclic systems in good yields and with complete diastereo- and chemoselectivity. Interestingly, its scope differs from that of previously reported annulations based on precious metal catalysts, specifically rhodium and palladium. Noticeably, density functional theory calculations confirm that the mechanism of the reaction is also different from those proposed for these other catalysts.

Palladium- and Brønsted acid-catalyzed enantio-, site- and E/Z-selective addition of alkylidenecyclopropanes with imines

Transition-metal catalyzed functionalization of ACPs has been widely investigated in cycloaddition and 1,3-difunctionalization reactions. However, the transition metal catalyzed nucleophilic reactions of ACPs have rarely been reported. In this article, an enantio-, site- and E/Z-selective addition of ACPs with imines for the synthesis of dienyl substituted amines has been developed via palladium- and Brønsted acid co-catalysis. A range of synthetically valuable dienyl substituted amines were effectively prepared with good to excellent yields and excellent enantio- and E/Z-selectivities.

Palladium‐Catalyzed Tandem Cycloisomerization/Cross‐Coupling of Carbonyl‐ and Imine‐Tethered Alkylidenecyclopropanes

Pd⁰ catalysts featuring phosphorus‐based monodentate ligands can detour the reactivity of carbonyl‐tethered alkylidenecyclopropanes (ACPs) from standard (3+2) cycloadditions towards tandem cycloisomerization/cross‐coupling processes. This new reactivity lies on the formation of key π‐allyl oxapalladacyclic intermediates, which are subsequently trapped with external nucleophilic partners, instead of undergoing canonical C−O reductive eliminations. Importantly, the use of imine‐tethered ACP's is also feasible. Therefore, the method provides a straightforward and stereoselective entry to a wide variety of highly functionalized cyclic alcohols and amines.

Highly Enantioselective Cobalt-Catalyzed (3+2) Cycloadditions of Alkynylidenecyclopropanes

Low-valent cobalt complexes equipped with chiral ligands can efficiently promote highly enantioselective (3+2) cycloadditions of alkyne-tethered alkylidenecyclopropanes. The annulation allows to assemble bicyclic systems containing five-membered rings in good yields and with excellent enantiomeric ratios. We also present a mechanistic discussion based on experimental and computational data, which support the involvement of Co^I /Co^III catalytic cycles.

Cycloaddition of cyclopropanes for the elaboration of medium-sized carbocycles

The stereocontrolled formation of medium-sized carbocycles is a major goal in modern organic chemistry due to their widespread occurrence in natural products and pharmaceutically active ingredients. One approach consists in the use of cycloaddition reactions which notably results in high selectivities and atom-economy. To this end, cyclopropanes are ideal substrates since they can provide readily functionalized three- or five-carbon synthons. Herein we report advances made in cycloaddition reactions of cyclopropanes towards the synthesis of medium-sized carbocycles via transition metal catalysis or Lewis acid catalysis.

[C^N]-Alkenyl Gold(III) Complexes by Proximal Ring-Opening of (2-Pyridyl)alkylidenecyclopropanes: Mechanistic Insights

Pyridine-substituted alkylidenecyclopropanes (Py-ACPs) react with gold(III) salts under mild reaction conditions through an unprecedented, proximal ring-opening pathway, to generate highly appealing, catalytically active pyridine alkenyl [C^N]-gold(III) species. Mechanistic studies reveal that the activation of the C-C bond of the ACP takes place through an unusual concerted, σ-bond metathesis type-process.

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.