Rapid ruthenium-catalyzed synthesis of pyranopyrandiones by reconstructive carbonylation of cyclopropenones involving C[bond]C bond cleavage

Novel Brønsted Acid Catalyzed C-C Bond Activation and α-Alkylation of Ketones

A novel approach for the α-alkylation of ketones was developed using Brønsted acid-catalyzed C-C bond cleavage. Both aromatic and aliphatic ketones reacted smoothly with 2-substituted 1,3-diphenylpropane-1,3-diones to afford α-alkylation products with high yields and with excellent regioselectivity, in which the 1,3-dicarbonyl group acted as a leaving group in the presence of the catalyst TfOH. Mechanism experiments showed that the β-C-C bond cleavage of diketone and the shift of the equilibrium towards the enol formation from ketone are driving forces that induce the desired products.

Phosphine-catalyzed activation of cyclopropenones: a versatile C3 synthon for (3+2) annulations with unsaturated electrophiles

We herein report a phosphine-catalyzed (3 + 2) annulation of cyclopropenones with a wide variety of electrophilic π systems, including aldehydes, ketoesters, imines, isocyanates, and carbodiimides, offering products of butenolides, butyrolactams, maleimides, and iminomaleimides, respectively, in high yields with broad substrate scope. An α-ketenyl phosphorous ylide is validated as the key intermediate, which undergoes preferential catalytic cyclization with aldehydes rather than stoichiometric Wittig olefinations. This phosphine-catalyzed activation of cyclopropenones thus supplies a versatile C3 synthon for formal cycloadditon reactions.

How Strain-Release Determines Chemoselectivity: A Mechanistic Study of Rhodium-Catalyzed Bicyclo[1.1.0]butane Activation

Bicyclo[1.1.0]butane (BCB) derivatives are versatile coupling partners, and various reaction modes for their activation and transformation have been proposed. In this work, three BCB-activation modes in Rh-catalyzed BCB transformations that construct diastereoselective α-quaternary β-lactones were investigated by density functional theory calculations. Our results show that, compared with C1-C3 insertion and C-C3 oxidative addition, C2-C3 oxidative addition is more favorable. The whole catalytic cycle involves five main steps: C-H activation, oxidative addition, β-C elimination/reductive elimination, Rh walking, and aldehyde insertion/protonation. Independent gradient model, intrinsic reaction coordinate, distortion-interaction energy, and Laplacian electron-density analyses were carried out to investigate the mode of BCB activation. Our calculation also showed that aldehyde-insertion is the diastereoselectivity determining step, which is controlled by the steric effect between the ligand, methyl group, and aldehyde.

Heterocycles from cyclopropenones

Great attention has been paid to cyclopropenones as they are present in many natural sources. Various synthesized cyclopropenone derivatives also show a wide range of biological activities. The cyclopropenone derivatives undergo a variety of reactions such as ring-opening reactions, isomerization reactions, C-C coupling reactions, C-H activation, cycloaddition reactions, thermal and photo-irradiation reactions, and acid-base-catalyzed reactions under the influence of various chemical reagents (electrophiles, nucleophiles, radicals, and organometallics) and external forces (heat and light). Many previous reviews have dealt with the chemistry and reactions of cyclopropenones. However and to the best of our knowledge, the utility of cyclopropenones in the synthesis of heterocycles has not been reported before. Therefore, it would be interesting to shed light on this new topic. The present review article provides, for the first time, a comprehensive compilation of synthetic methods for the synthesis of various heterocyclic ring systems, as a significant family in the field of organic chemistry.

Mechanistic differences between aryl iodide electrophiles and pronucleophiles in Pd-catalyzed coupling with cyclopropenes: a DFT study

Computational studies were carried out to investigate the mechanisms of Pd-catalyzed ring-opening reactions of cyclopropenes with pronucleophiles (H-Nu) and aryl iodide electrophiles, respectively.

Cascade Ring-Opening Dual Halogenation of Cyclopropenones with Saturated Oxygen Heterocycles

Represented is a CuX₂- or I₂-promoted ring-opening dual halogenation of cyclopropenones with saturated oxygen heterocycles, providing an efficient method for the synthesis of 3-haloacrylates. The ring-opening reaction enables the construction of two C-X (X = Cl, Br, or I) bonds and a C-O bond as well as the cleavage of two C-O bonds and a C-C bond in a single step. This protocol is highly atom economical, has an excellent substrate scope, and exhibits the ability for gram-scale reaction.

Enantioselective palladium-catalyzed C(sp2)-C(sp2) σ bond activation of cyclopropenones by merging desymmetrization and (3 + 2) spiroannulation with cyclic 1,3-diketones

Catalytic asymmetric variants for functional group transformations based on carbon–carbon bond activation still remain elusive. Herein we present an unprecedented palladium-catalyzed (3 + 2) spiro-annulation merging C(sp²)–C(sp²) σ bond activation and click desymmetrization to form synthetically versatile and value-added oxaspiro products. The operationally straightforward and enantioselective palladium-catalyzed atom-economic annulation process exploits a TADDOL-derived bulky P-ligand bearing a large cavity to control enantioselective spiro-annulation that converts cyclopropenones and cyclic 1,3-diketones into chiral oxaspiro cyclopentenone–lactone scaffolds with good diastereo- and enantio-selectivity. The click-like reaction is a successful methodology with a facile construction of two vicinal carbon quaternary stereocenters and can be used to deliver additional stereocenters during late-state functionalization for the synthesis of highly functionalized or more complex molecules.

An unprecedented palladium-catalyzed (3 + 2) spiro-annulation merging C–C bond activation and desymmetrization was developed for the enantioselective construction of synthetically versatile and value-added oxaspiro products with up to 95% ee.

Ruthenium-Catalyzed Cycloadditions to Form Five-, Six-, and Seven-Membered Rings

Ruthenium-catalyzed cycloadditions to form five-, six-, and seven-membered rings are summarized, including applications in natural product total synthesis. Content is organized by ring size and reaction type. Coverage is limited to processes that involve formation of at least one C-C bond. Processes that are stoichiometric in ruthenium or exploit ruthenium as a Lewis acid (without intervention of organometallic intermediates), ring formations that occur through dehydrogenative condensation-reduction, σ-bond activation-initiated annulations that do not result in net reduction of bond multiplicity, and photochemically promoted ruthenium-catalyzed cycloadditions are not covered.

Ag2O-promoted ring-opening reactions of cyclopropenones with oximes

Ag2O-promoted ring-opening reactions of cyclopropenones with oximes is disclosed in this work, providing a direct route to 1,3-oxazinones. This method highlights a new reactivity of cyclopropenones which undergo 1,4-addition with oximes followed by β-carbon elimination to in situ generate a α-carbonyl ketene intermediate.

Selective [3 + 2] Cycloaddition of Cyclopropenone Derivatives and Elemental Chalcogens

A highly efficient method is disclosed for the synthesis of 1,2-dichalcogen heterocycles via [3 + 2] cycloaddition of cyclopropenone derivatives and elemental chalcogens. Different from other cyclopropenone derivatives, cyclopropenselenones undergo unprecedented rearrangement with elemental sulfur. The features of this protocol include mild reaction conditions, high efficiency, excellent atom economy, gram-scale ability, and good regioselectivity.

Synthesis of 4-ethenyl quinazolines via rhodium(iii)-catalyzed [5 + 1] annulation reaction of N-arylamidines with cyclopropenones

An unprecedented synthesis of 4-ethenyl quinazolines/2-benzoyl quinazolines via Rh(iii)-catalyzed C–H annulation reaction was reported.

Organocatalytic C–C bond activation of cyclopropenones for ring-opening formal [3 + 2] cycloaddition with isatins

Cyclopropenones were first applied as potential 3C synthons in ring-opening formal cycloaddition with isatins via an organocatalytic C–C bond activation strategy.

Nucleophilicity and P-C Bond Formation Reactions of a Terminal Phosphanido Iridium Complex

The diiridium complex [{Ir(ABPN2)(CO)}2(μ-CO)] (1; [ABPN2](-) = [(allyl)B(Pz)2(CH2PPh2)](-)) reacts with diphenylphosphane affording [Ir(ABPN2)(CO)(H) (PPh2)] (2), the product of the oxidative addition of the P-H bond to the metal. DFT studies revealed a large contribution of the terminal phosphanido lone pair to the HOMO of 2, indicating nucleophilic character of this ligand, which is evidenced by reactions of 2 with typical electrophiles such as H(+), Me(+), and O2. Products from the reaction of 2 with methyl chloroacetate were found to be either [Ir(ABPN2)(CO)(H)(PPh2CH2CO2Me)][PF6] ([6]PF6) or [Ir(ABPN2)(CO)(Cl)(H)] (7) and the free phosphane (PPh2CH2CO2Me), both involving P-C bond formation, depending on the reaction conditions. New complexes having iridacyclophosphapentenone and iridacyclophosphapentanone moieties result from reactions of 2 with dimethyl acetylenedicarboxylate and dimethyl maleate, respectively, as a consequence of a further incorporation of the carbonyl ligand. In this line, the terminal alkyne methyl propiolate gave a mixture of a similar iridacyclophosphapentanone complex and [Ir(ABPN2){CH═C(CO2Me)-CO}{PPh2-CH═CH(CO2Me)}] (10), which bears the functionalized phosphane PPh2-CH═CH(CO2Me) and an iridacyclobutenone fragment. Related model reactions aimed to confirm mechanistic proposals are also studied.

Mechanisms and stereoselectivities of the Rh(i)-catalyzed carbenoid carbon insertion reaction of benzocyclobutenol with diazoester

Mechanisms and stereoselectivities of a Rh(i)-catalyzed carbenoid carbon insertion reaction of benzocyclobutenol with diazoester have been investigated using the DFT method.

Mild synthesis of chalcones via rhodium(III)-catalyzed C-C coupling of arenes and cyclopropenones

A Rh(III)-catalyzed aryl C-H bond insertion into cyclopropenones via a C-H activation pathway has been reported. A series of arenes bearing directing groups such as 2-pyridyl, 2-pyrimidyl, N-pyrazyl, and oxime can be applicable, providing chalcones in excellent yields under mild conditions. Several possible Rh(III) intermediates in this reaction were investigated.