Gold-Catalyzed Cycloisomerization of Yne-Vinylidenecyclopropanes: A Three-Carbon Synthon for [3+2] Cycloadditions

Gold(i)-catalyzed cycloisomerization of alcohol or amine tethered-vinylidenecyclopropanes providing access to morpholine, piperazine or oxazepane derivatives: a carbene versus non-carbene process

A gold(i)-catalyzed adjustable intramolecular cyclization of alcohol or amine tethered-vinylidenecyclopropanes (VDCPs).

Oxidation of Enones for Regioselective [3+2] Cycloaddition through γ-Enone Radical Intermediates

Herein, an oxidization reaction of enones with a Cu^II complex that leads to a new type of regioselective [3+2] cycloaddition is reported. Highly functionalized cyclopentenes and spirocyclic compounds are obtained in moderate-to-good yields. This cycloaddition reaction occurred through the formation of γ-enone radicals, providing a rarely explored reactivity pattern for enones.

Rh(i)-Catalyzed stereoselective intramolecular cycloaddition reactions of ene-vinylidenecyclopropanes for the construction of fused 6,5-bicyclic skeletons with a quaternary all-carbon stereocenter

Rh(i)-catalyzed asymmetric [3 + 2] cycloadditions of ene-VDCPs are demonstrated, producing cyclic ring structures with an all-carbon quaternary stereocenter in good yields with excellent enantioselectivities.

Rh(i)-Catalyzed intramolecular [3 + 2] cycloaddition reactions of yne-vinylidenecyclopropanes

A Rh(i)-catalyzed intramolecular [3 + 2] cycloaddition reaction of yne-vinylidenecyclopropanes has been developed, providing fused [6.5]-bicyclic products in moderate to good yields.

Recent Advances in Transition-Metal-Catalyzed/Mediated Transformations of Vinylidenecyclopropanes

Vinylidenecyclopropanes (VDCPs), having an allene moiety connected to a highly strained cyclopropyl group, have attracted a substantial amount of attention since they are fascinating building blocks for organic synthesis. During recent years, the reactions of VDCPs in the presence of a Lewis acid or a Brønsted acid and those induced by heat or light have experienced significant advancements due to the unique structural and electronic properties of VDCPs. Transition-metal-catalyzed reactions of VDCPs were not intensely investigated until the last 5 years. Recently, significant progress has been made in transition-metal-catalyzed transformations of VDCPs, and they have emerged as a new direction for the chemistry of strained small rings, especially when new types of functionalized vinylidenecyclopropanes (FVDCPs) are used as substrates. To date, many interesting transformations have been explored using these novel VDCPs under the catalysis of transition metals, such as gold, palladium, or rhodium, and various novel and useful heterocyclic or polycyclic compounds have been generated. These new findings have enriched the chemistry of strained small carbocycles. This Account will describe the transition-metal-catalyzed transformations of VDCPs recently developed in our laboratory and by other groups. The chemistry of Au-catalyzed VDCPs has been enriched and extensively developed by our group. In this respect, a new process for generating gold carbenes from VDCPs has been disclosed. The reactivity of these new gold carbenoid species was fully investigated, and many novel reaction modes based on these new gold carbenoid species were explored, including oxidation reactions, intramolecular cyclopropanations, C(sp³)-H bond functionalizations, and C-O bond cleavage reactions. Rh-catalyzed reactions of VDCPs are another key field of transition-metal-catalyzed reactions of VDCPs. In particular, rhodium-catalyzed cycloadditions, Pauson-Khand reactions, and C-H bond activations of FVDCPs have been explored in detail by our group. A new trimethylenemethane rhodium (TMM-Rh) complex generated from VDCPs was discovered and utilized as an electrophilic Rh-π-allyl precursor. Moreover, some unprecedented highly regio- and enantioselective asymmetric allylic substitutions via this novel TMM-Rh complex were developed with different kinds of nucleophiles. This Account will also summarize the recent advances in palladium-, copper-, and iron-catalyzed cycloisomerization reactions of VDCPs reported by our group and others. These reactions always afford the desired products with excellent chemo-, regio-, diastereo-, and enantioselectivities, which will make them highly valuable for the synthesis of key scaffolds in natural products and pharmaceutical molecules in the future.

Gold- and silver-catalyzed intramolecular annulation and rearrangement of aniline-linked 1,6-enynes containing methylenecyclopropanes

A new synthetic approach for the construction of 1,2-dihydroquinolines having a methylenecyclopropane moiety or a cyclobutene moiety has been developed from gold- and silver-catalyzed annulation of N-tethered 1,6-enynes containing methylenecyclopropanes.

Rhodium/Silver Synergistic Catalysis in Highly Enantioselective Cycloisomerization/Cross Coupling of Keto-Vinylidenecyclopropanes with Terminal Alkynes

A rhodium/silver synergistic catalysis has been established, enabling cycloisomerization/cross coupling of keto-vinylidenecyclopropanes (VDCPs) with terminal alkynes toward the regio- and enantioselective formation of diversified tetrahydropyridin-3-ol tethered 1,4-enynes in good yields and high ee values. In this synergistic catalysis, Rh(I) and Ag(I) catalysts selectively activate keto-VDCP substrates and terminal alkynes to generate the π-allyl Rh(III) complex of oxa-rhodacyclic intermediate and Ag alkynyl intermediate, respectively. The rapid transmetalation of alkynyl groups from Ag to Rh is proposed to play a key role in realizing the regioselective cleavage of the distal bond of the three-membered ring in this transformation.

Enantioselective gold(i)-catalyzed rearrangement of cyclopropyl-substituted 1,6-enynes into 2-oxocyclobutyl-cyclopentanes

A gold(i)-catalyzed cycloisomerization/ring expansion sequence allows the highly enantioselective synthesis of 2-oxocyclobutylcyclopentane derivatives from cyclopropyl-substituted enynes (up to 99% ee).

Gold(I) catalysed sequential dehydrative cyclisation/intermolecular [4 + 2] cycloaddition of alkynyldienols onto activated alkynes/alkenes: a facile route to substituted norbornadienes/norbornenes

One-pot synthesis of highly substituted norbornadienes/norbornenes via gold-catalysed dehydrative cyclisation of alkynyldienols, followed by intermolecular [4 + 2] cycloaddition of in situ generated cyclopentadiene and activated alkynes/alkenes is described. The precursors, alkynyldienols, are obtained via sequential Sonogashira cross-coupling of 3-bromoenals, alkyne addition and reduction. Yields of the enynals and multisubstituted norbornadienes in all the cases are good to excellent.

An unexpected three-component reaction of 2-alkylenecyclobutanone and N′-(2-alkynylbenzylidene)hydrazide with water

A silver(i)-catalyzed three-component reaction of 2-alkylenecyclobutanone, N′-(2-alkynylbenzylidene)hydrazide with water gives rise to 3-(pyrazolo[5,1-a]isoquinolin-1-yl)propanoic acids in good yields through 6-endo cyclization, [3 + 2] cycloaddition, and rearrangement.