Efficient Synthesis of Polycyclic γ‐Lactams by Catalytic Carbonylation of Ene‐Imines via Nickelacycle Intermediates

The nickel(0)‐catalyzed carbonylative cycloaddition of 1,5‐ and 1,6‐ene‐imines with carbon monoxide (CO) is reported. Key to this reaction is the efficient regeneration of the catalytically active nickel(0) species from nickel carbonyl complexes such as [Ni(CO)₃L]. A variety of tri‐ and tetracyclic γ‐lactams were thus prepared in excellent yields with 100 % atom efficiency. Preliminary results on asymmetric derivatives promise potential in the synthesis of enantioenriched polycyclic γ‐lactams.     

Nickel(0)‐Catalyzed Enantioselective [3+2] Annulation of Cyclopropenones and α,β‐Unsaturated Ketones/Imines

Ni⁰‐catalyzed chemo‐ and enantioselective [3+2] cycloaddition of cyclopropenones and α,β‐unsaturated ketones/imines is described. This reaction integrates C?C bond cleavage of cyclopropenones and enantioselective functionalization by carbonyl/imine group, offering a mild approach to γ‐alkenyl butenolides and lactams in excellent enantioselectivity (88–98 % ee) through intermolecular C?C activation.     

Regioselective CC bond formation between ethylene and α-naphthylcarbaldimines catalyzed by Ru3(Co)12: NMR spectroscopic investigations on the proceeding of the reaction

The reaction of ethylene with imines derived from α-naphthylcarbaldehyde catalyzed by Ru₃(CO)₁₂ leads to the selective and quantitative formation of products in which one molecule of ethylene has been inserted into the CH bond in ortho position with respect to the exocyclic imine substituent. The stoichiometric reaction of the same ligands with Ru₃(CO)₁₂ leads to dinuclear ruthenium carbonyl complexes showing the same regioselectivity of CH activation but the hydrogen atom is shifted in an intramolecular hydrogen transfer reaction towards the former imine carbon atom. If the catalytic alkylation of α-naphthylcarbaldimines is monitored by NMR the occurrence of the dinuclear product of the stoichiometric reaction is observed before the reaction again quantitatively yields the imines bearing an ethyl group in 2-position of the naphthalene core. This proofs that there must be an equilibrium between the dinuclear ruthenium carbonyl complex which is also observed if α-naphthylcarbaldimines are treated with an equimolar amount of Ru₃(CO)₁₂ and another ruthenium compound where the ethylene might be inserted catalytically into a ruthenium carbon bond.     

Intermolecular [2+2+1] Carbonylative Cycloaddition of Aldehydes with Alkynes,and Subsequent Oxidation to γ‐Hydroxybutenolides by a Supported Ruthenium Catalyst

Intermolecular [2+2+1] carbonylative cycloaddition of aldehydes with alkynes and subsequent oxidation to γ‐hydroxybutenolides is achieved using a supported ruthenium catalyst. A ceria‐supported ruthenium catalyst promotes the reaction efficiently, even with an ambient pressure of CO or without external CO, thus giving the corresponding γ‐hydroxybutenolide derivatives in good to high yields. Moreover this catalyst can be reused with no loss of activity.     

Intermolecular [2+2+1] Carbonylative Cycloaddition of Aldehydes with Alkynes,and Subsequent Oxidation to γ‐Hydroxybutenolides by a Supported Ruthenium Catalyst

Intermolecular [2+2+1] carbonylative cycloaddition of aldehydes with alkynes and subsequent oxidation to γ‐hydroxybutenolides is achieved using a supported ruthenium catalyst. A ceria‐supported ruthenium catalyst promotes the reaction efficiently, even with an ambient pressure of CO or without external CO, thus giving the corresponding γ‐hydroxybutenolide derivatives in good to high yields. Moreover this catalyst can be reused with no loss of activity.     

Catalytic Divergent [3+3]‐ and [3+2]‐Cycloaddition by Discrimination Between Diazo Compounds

Highly selective divergent cycloaddition reactions of enoldiazo compounds and α‐diazocarboximides catalyzed by copper(I) or dirhodium(II) have been developed. With tetrakis(acetonitrile)copper(I) tetrafluoroborate as the catalyst epoxypyrrolo[1,2‐a]azepine derivatives were prepared in good yields and excellent diastereoselectivities through the first reported [3+3]‐cycloaddition of a carbonyl ylide. Use of Rh₂(pfb)₄ or Rh₂(esp)₂ directs the reactants to regioselective [3+2]‐cycloaddition generating cyclopenta[2,3]pyrrolo[2,1‐b]oxazoles with good yields and excellent diastereoselectivities.     

Thermal decomposition of some ruthenium carbonyl hydrides

The thermal stability of α-H₄Ru₄(CO)₁₂, H₄Ru₄(CO)₁₀P₂, H₄Ru₄(CO)₉P₃, H₄Ru₄(CO)₈P₄ (where P=triphenylphosphine) has been investigated by differential scanning calorimetry and by thermogravimetric analysis under argon dynamic atmosphere.The TG curves of the triphenylphosphine substituted derivatives of α-H₄Ru₄(CO)₁₂ suggest the release of the carbonyl and of the phenyl groups through a not well-defined pattern and overlapping decomposition reactions up to the retention of phosphorus in the residue, while α-H₄Ru₄(CO)₁₂ decomposes to metallic ruthenium. The decomposition heat of α-H₄Ru₄(CO)₁₂ and the isomerization heat of H₄Ru₄(CO)₈P₄ have been evaluated.     

Catalyst‐Dependent Divergent Synthesis of Pyrroles from 3‐Alkynyl Imine Derivatives: A Noncarbonylative and Carbonylative Approach

A novel Ru⁰‐ and Rh^I‐catalyzed noncarbonylative and carbonylative cycloisomerization of readily available 3‐alkynyl imine derivatives has been developed to provide 3,4‐fused or nonfused pyrrole derivatives efficiently in moderate to excellent yields. The key steps involve the formation of a ruthenium carbenoid intermediate or a rhodacycle intermediate, respectively. In these reactions, CO can serve as a ligand or a reagent.     

Stereoselective synthesis of trans β-lactams via palladium/N-heterocyclic carbene-catalyzed carbonylative [2+2] cycloaddition

The carbonylative [2+2] cycloaddition of benzyl chlorides and allyl derivatives with imines and CO for synthesis of β-lactam is effectively catalyzed by palladium/N-heterocyclic carbene complex. The desired β-lactam could be obtained in good to excellent yields (61–96%) with excellent regioselectivities (trans/cis > 95:5) and chiral lactams could be obtained with moderate diastereoselectivities. The KIE experimental studies have revealed that the C–H cleavage is most likely to be the rate-limiting step for the carbonylative cycloaddition.     

Towards the Development of a Selective Ruthenium‐Catalyzed Hydroformylation of Olefins

The ruthenium‐catalyzed hydroformylation of 1‐ and 2‐octene to give preferentially the corresponding linear aldehyde is reported. The catalyst system comprising of Ru₃(CO)₁₂ and an imidazole‐substituted monophosphine ligand allows for high chemo‐ and regioselectivity. The hydroformylation proceeds with unprecedented rates for a ruthenium‐based catalyst.     

PPh3⋅HBr‐DMSO Mediated Expedient Synthesis of γ‐Substituted β,γ‐Unsaturated α‐Ketomethylthioesters and α‐Bromo Enals: Application to the Synthesis of 2‐Methylsulfanyl‐3(2 H)‐furanones

An efficient chemoselective general procedure for the synthesis of γ‐substituted β,γ‐unsaturated α‐ketomethylthioesters from α,β‐unsaturated ketones has been achieved through an unprecedented PPh₃?HBr‐DMSO mediated oxidative bromination and Kornblum oxidation sequence. The newly developed reagent system serves admirably for the synthesis of α‐bromoenals from enals. Furthermore, AuCl₃‐catalyzed efficient access to 3(2H)‐furanones from the above intermediates under extremely mild conditions are described.     

Nucleophilic Cyclopropanation Reaction with Bis(iodozincio)methane by 1,4‐Addition to α,β‐Unsaturated Carbonyl Compounds

Treatment of α,β‐unsaturated ketones with an electrophilic site at the γ‐position in the presence of trimethylsilyl cyanide with bis(iodozincio)methane afforded the (Z)‐silyl enol ether of the β‐cyclopropyl substituted ketone in good yields. The reaction proceeds by 1,4‐addition to form an enolate, and its sequential intramolecular nucleophilic attack to an adjacent electrophilic site. The reaction of γ‐ethoxycarbonyl‐α,β‐unsaturated ketone and bis(iodozincio)methane in the presence of trimethylsilyl cyanide afforded 1‐ethoxy‐1‐trimethylsiloxycyclopropane derivatives, which can be regarded as the homoenolate equivalent. Additionally, reaction of the obtained homoenolate equivalents with imines give 1‐(E)‐alkenyl‐2‐(1‐aminoalkyl)alkanols diastereoselectively.     

Microwave‐Assisted,Rhodium(III)‐Catalyzed N‐Annulation Reactions of Aryl and α,β‐Unsaturated Ketones with Alkynes

New Rh^III‐catalyzed, one‐pot N‐annulation reactions of aryl and α,β‐unsaturated ketones with alkynes in the presence of ammonium acetate have been developed. Under microwave irradiation conditions, the processes lead to rapid formation of the respective isoquinoline and pyridine derivatives with efficiencies that are strongly dependent on the steric nature of the aryl ring and enone substituents. By employing this protocol, a variety of isoquinoline and pyridine derivatives were prepared in high yields. In addition, a new one‐pot approach to the synthesis of pyridines, involving four‐component reactions of ketones, formaldehyde, NH₄OAc, and alkynes, has been uncovered. This process takes place through a route involving initial aldol condensation of the ketone with formaldehyde to generate a branched α,β‐unsaturated ketone that then undergoes Rh^III‐catalyzed N‐annulation with NH₄OAc and the alkyne.     

Cluster Chemistry: XVII.Radical ion-initiated synthesis of ruthenium cluster carbonyls containing tertiary phosphines,phosphites, arsines,SbPh3, or isocyanides

The syntheses of over sixty known and new derivatives of Ru₃(CO)₁₂ and H₄Ru₄(CO)₁₂ by substitution reactions initiated by sodium diphenylketyl are described. The range of ligands studied includes isocyanides, tertiary phosphines and phosphites, tertiary arsines and SbPh₃. The reactions are characterised by high degrees of specificity and conversion: under mild conditions up to four ligands can be introduced. Comparisons with the corresponding thermally induced reactions are made in several cases. The reactions provide routes to mixed ligand derivatives of the cluster carbonyls, although account of relative Lewis base strengths of the ligands may have to be taken. Possible mechanisms of these reactions are discussed briefly, as are the IR ν (CO) spectra of the Ru₃ (CO)_12-nL_n complexes.     

Synthesis and isomerization of N-α-aza-heteroaryl-β-lactams

The [2+2] carbonylative cycloaddition of N-α-aza-heteroaryl substituted imines with allyl bromide led partially to β-lactams, which underwent isomerization to the more stable α,β-unsaturated carbonyl compound. Pyrimidinone derivatives together with doubly unsaturated amides represent the remaining isolated products. The strong electron-withdrawing effect of the two α-aza-heterocycles linked to the nitrogen atom and to the C4 of the 2-azetidinone structure could give a ring expansion, through a 2-azetinone intermediate that affords the pyrimidinone compounds. The substituted amides, instead, should result from a ring-opening reaction of the β-lactam.     

Nickel‐Catalyzed Synthesis of N‐Aryl‐1,2‐dihydropyridines by [2+2+2] Cycloaddition of Imines with Alkynes through T‐Shaped 14‐Electron Aza‐Nickelacycle Key Intermediates

Despite there being a straightforward approach for the synthesis of 1,2‐dihydropyridines, the transition‐metal‐catalyzed [2+2+2] cycloaddition reaction of imines with alkynes has been achieved only with imines containing an N‐sulfonyl or ‐pyridyl group. Considering the importance of 1,2‐dihydropyridines as useful intermediates in the preparation of a wide range of valuable organic molecules, it would be very worthwhile to provide novel strategies to expand the scope of imines. Herein we report a successful expansion of the scope of imines in nickel‐catalyzed [2+2+2] cycloaddition reactions with alkynes. In the presence of a nickel(0)/PCy₃ catalyst, a reaction with N‐benzylidene‐P,P‐diphenylphosphinic amide was developed. Moreover, an application of N‐aryl imines to the reaction was also achieved by adopting N‐heterocyclic carbene ligands. The isolation of an (η²‐N‐aryl imine)nickel(0) complex containing a 14‐electron nickel(0) center and a T‐shaped 14‐electron five‐membered aza‐nickelacycle is shown. These would be considered as key intermediates of the reaction. The structure of these complexes was unambiguously determined by NMR spectroscopy and X‐ray analyses.     

Synthesis of <Emphasis Type="Italic">ms</Emphasis>- and β-substituted ruthenium(II) porphyrinates

The reactions of 5,10,15,20-tetraphenylporphine, 2,3,7,8,12,13,17,18-octaethylporphine, and tetra(4-methoxyphenyl)porphine with Ru₃(CO)₁₂ in boiling phenol were studied by spectrophotometry. The following compounds were synthesized and identified: Ru²⁺(CO)(H₂O) 5,10,15,20-tetraphenylporphyrinate, Ru²⁺(CO)(H₂O) 2,3,7,8,12,13,17,18-octaethylporphyrinate, Ru²⁺(CO)(Py) 2,3,7,8,12,13,17,18-octaethylporphyrinate, and Ru²⁺(CO)(H₂O) tetra(4-methoxyphenyl)porphyrinate. The strong electronic effect of the substituents on the reactivity of the tetrapyrrole cycle during the formation of the corresponding porphyrinates was established.     

A highly selective cobalt-catalyzed carbonylative cyclization of internal alkynes with carbon monoxide and organic thiols

Despite the fact that many transition-metal-catalyzed reactions of organosulfur compounds with internal alkynes are ineffective, cobalt carbonyl (Co₂(CO)₈) is an excellent catalyst for carbonylative cyclization of internal alkynes with carbon monoxide. When Co₂(CO)₈-catalyzed reactions of internal alkynes with organic thiols are conducted in acetonitrile under 4 MPa pressure of carbon monoxide, thiolative lactonization of internal alkynes successfully takes place with incorporation of two molecules of CO. This carbonylation provides a useful tool to prepare the corresponding α,β-unsaturated γ-thio-γ-lactones (butenolide derivatives) in good yields. In the cases of unsymmetrical alkynes, such as 2-octyne and 6-methyl-2-heptyne, the thiolative lactonization proceeds with moderate regioselectivity to give the butenolide derivatives on which the carbonyl group preferentially bonds to the less hindered acetylenic carbon. Mechanistic pathways about the present thiolative lactonization are also discussed.     

Stereoselective Construction of 1,3‐Disilylcyclopentane Derivatives by Scandium‐Catalyzed [3+2] Cycloaddition of Allylsilanes to β‐Silylenones

The Sc(OTf)₃‐catalyzed [3+2] cycloaddition of allylsilanes to β‐silyl‐α,β‐unsaturated ketones (β‐silylenones) has been developed to form five‐membered syn‐1,3‐disilylketones diastereoselectively through the rearrangement of the silicon substituents on the allylsilane. Stabilization of the carbocation intermediates by a double silicon effect plays a key role in directing the course of the reaction to favor the [3+2] cycloaddition pathway over simple allylation.     

Asymmetric hydrogenation of α-β unsaturated ketones with chiral phosphinecobalt carbonyl catalysts

The hydrogenation of α-β unsaturated ketones with Co₂(CO)₆[PPh₂-Neomenthyl]₂ as catalyst gives optically active ketones with optical yields of 1.4–16%.