Rhodium(I)-Catalyzed Pauson–Khand-type [3 + 2 + 1] Cycloaddition Reaction of Ene-Vinylidenecyclopropanes and CO: A Highly Regio- and Stereoselective Synthetic Approach for the Preparation of Aza- and Oxa-Bicyclic Compounds

Visible-light mediated cascade cyclization of ene-vinylidenecyclopropanes: access to fluorinated heterocyclic compounds

A visible-light mediated fluorinated cyclization of ene-vinylidenecyclopropanes along with mechanistic investigations is presented.

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.

Rhodium-Catalyzed Intermolecular Carbonylative [2 + 2 + 1] Cycloaddition of Alkynes Using Alcohol as the Carbon Monoxide Source for the Formation of Cyclopentenones

A highly regioselective rhodium-catalyzed intermolecular carbonylative [2 + 2 + 1] cycloaddition of alkynes using alcohol as a CO surrogate to access 4-methylene-2-cyclopenten-1-ones has been developed. In this transformation, the alcohol performs multiple roles, including generating the Rh-H intermediate, functioning as the CO source, and assisting in the isomerization of the alkyne. Alkynes can act as both the olefin and the alkyne partner in the cyclopentenone core.

New Initiation Modes for Directed Carbonylative C-C Bond Activation: Rhodium-Catalyzed (3 + 1 + 2) Cycloadditions of Aminomethylcyclopropanes

Under carbonylative conditions, neutral Rh(I)-systems modified with weak donor ligands (AsPh₃ or 1,4-oxathiane) undergo N-Cbz, N-benzoyl, or N-Ts directed insertion into the proximal C–C bond of aminomethylcyclopropanes to generate rhodacyclopentanone intermediates. These are trapped by N-tethered alkenes to provide complex perhydroisoindoles.

Palladium-catalyzed intramolecular rearrangement of vinylidenecyclopropanes through C–C bond activation

An intramolecular rearrangement of vinylidenecyclopropanes to dimethylenecyclopropanes through C–C bond activation has been developed.

Rh(I)-catalyzed Pauson-Khand-type cycloaddition reaction of ene-vinylidenecyclopropanes with carbon monoxide (CO)

An intramolecular Pauson-Khand type cycloaddition reaction of ene-vinylidenecyclopropanes with carbon monoxide has been established by using [Rh(COD)Cl](2) as the catalyst. The reaction was found to be highly efficient in solvents of 1,2-dichloroethane and 1,1,2,2-tetrachloroethane to give excellent yields of 90-99%. The reaction provides easy access to a series of fused 6,5-ring structures containing spiro-cyclopropane units that are useful for drug design and development. A mechanism of this cycloaddition process has been proposed accounting for structures of resulting products that were unambiguously assigned by X-ray diffractional analysis.