Novel rhodium-catalyzed cycloisomerization of 1,6-enynes with an intramolecular halogen shift

A new Rh-catalyzed 1,6-enyne cycloisomerization process with a pi-allyl rhodium species as the key intermediate is investigated. A halogen shift happened in this novel process. The synthesis of stereodefined alpha-halomethylene gamma-butyrolactones has been achieved using the readily accessible Rh catalysts.     

Gold-catalyzed hydroamination/cycloisomerization reaction of 1,6-enynes

An efficient Au(I) catalytic system is described for the hydroamination/cycloisomerization reaction of functionalized 1,6-enynes. The reaction leads to carbo- and heterocyclic amino derivatives in good to excellent yields. The cyclizations were conducted in the presence of PPh(3)AuCl/AgSbF(6) catalyst in THF or dioxane at room temperature. The use of allyloxycarbonyl carbamate has allowed the formation of free amino derivatives via sequential Au- and Pd-catalyzed reactions.     

Rhodium-catalyzed cycloisomerization of 1,6-enynes with an intramolecular halogen shift: reaction scope and mechanism

The rhodium(I)-species-catalyzed cycloisomerization reaction of a wide spectrum of 1,6-enynes with an unusual intramolecular halogen shift was investigated. This Rh-catalyzed enyne cyclization reaction represents a new process for the synthesis of stereodefined alpha-halomethylene-gamma-butyrolactones, lactams, tetrahydrofurans, pyrrolidines, and cyclopentanes. Coordinatively unsaturated rhodium species ([Rh(COD)Cl](2) + dppb + AgSbF(6)) only catalyzes the reaction with enyne substrates bearing a Z-form double bond, while neutral rhodium species (RhCl(PPh(3))(3)) could catalyze enyne substrates bearing a Z- or E-form double bond to form the desired products and has a wider substrate scopes. The mechanism of the reaction was studied by the employment of control experiments with different enyne isomers, and a pi-allyl rhodium intermediate was suggested to explain the formation of the cyclic products with an intramolecular halogen shift.     

Cobalt-catalyzed cycloisomerization of 1,6-enynes and allyl propargyl ethers

[reaction: see text] 1,6-Enynes and allyl propargyl ethers undergo a cobalt-catalyzed formal 5-endo-dig cyclization to form vinyl cyclopentenes and dihydrofurans, respectively. The use of equimolar amounts of dicobalt octacarbonyl and trimethyl phosphite affords optimum yields and improved selectivity for cycloisomerization vs alkene isomerization.     

Chiral diene-phosphine tridentate ligands for rhodium-catalyzed asymmetric cycloisomerization of 1,6-enynes

Asymmetric cycloisomerization of nitrogen-bridged 1,6-enynes proceeded in the presence of a cationic rhodium complex coordinated with a chiral diene/phosphine tridentate ligand to give high yields of chiral 3-azabicyclo[4.1.0]heptenes with high enantioselectivity.     

Iridium complex-catalyzed reaction of 1,6-enynes: cycloaddition and cycloisomerization

[reaction: see text] 1,6-Enynes reacted with monoynes to give cyclohexadiene derivatives in the presence of a catalytic amount of [Ir(cod)Cl](2)/ligand. DPPE was most suitable for cycloaddition. Diastereoselective cycloaddition was also possible. In the absence of monoynes, 1,6-enynes cycloisomerized to (Z)-1-alkylidene-2-methylenecyclopentane derivatives. DPPF was most suitable for cycloisomerization. These results are the first examples of highly Z-selective cycloisomerization.     

A theoretical investigation on the mechanism of the PtCl2-mediated cycloisomerization of heteroatom-tethered 1,6-enynes

A mechanistic study based on DFT theoretical calculations for the PtCl(2)-catalyzed formation of bicyclic adducts from heteroatom tethered 1,6-enynes is reported. Different reaction pathways have been taken into account and the results are discussed. This analysis clearly reveals that the kinetically preferred pathway involves an initial 6-endo-cyclization from a triggered reactant complex by pi-complexation of Pt(II) onto the alkyne to form a cyclopropyl platina-carbene intermediate, followed by a [1,2]-hydrogen shift.     

Iridium-catalyzed enantioselective cycloisomerization of nitrogen-bridged 1,6-enynes to 3-azabicylo[4.1.0]heptenes

A cationic iridium complex catalyzes a cycloisomerization of nitrogen-bridged 1,6-enynes to give 3-azabicyclo[4.1.0]heptenes in good to high yield. When an iridium-chiral diphosphine complex is used, the reaction proceeds enantiomerically to give chiral cyclopropanes fused by a six-membered ring system.     

Comparison of homogeneous and heterogeneous Ga(III) catalysis in the cycloisomerization of 1,6-enynes

We describe a study of the gallium(III)-catalyzed 1,6-enynes cycloisomerization reaction in both homogeneous and heterogeneous conditions. With GaBr₃ in homogeneous conditions, some particularities were observed in terms of selectivity compared to reported GaCl₃-catalyzed reactions. The transfer of the reaction in heterogeneous conditions was realized by supporting Ga(III) salts onto montmorillonite. Both systems were compared based on reaction times, conversion, and selectivity and showed complementary activities.     

Mechanistic and stereochemical aspects of the asymmetric cyclocarbonylation of 1,6-enynes with rhodium catalysts

NMR and kinetic investigations of the cyclocarbonylation of 1,6-enynes with cationic rhodium(i) catalysts, modified with atropisomeric diphosphines, disprove the involvement of carbonyl species for 1,6-enyne activation; low-temperature catalysis, with molecular sieves as the carbon monoxide reservoir, is highly enantioselective (ee up to 97%).     

Immobilized cobalt/rhodium heterobimetallic nanoparticle-catalyzed silylcarbocylization and carbonylative silylcarbocyclization of 1,6-enynes

Reaction of 1,6-enynes with a hydrosilane in the presence of immobilized cobalt/rhodium bimetallic nanoparticles gives 2-methyl-1-silylmethylidene-2-cyclopentanes in the absence of carbon monoxide and 2-formylmethyl-1-silylmethylidene-2-cyclopentanes under 1 atm of carbon monoxide, respectively. [reaction: see text]     

cis-chloropalladation of 1,6-enynes

A PdCl(2)-catalyzed cis-chloropalladation-cyclization reaction of various 1,6-enyne substrates was developed. This Pd-catalyzed enyne cyclization reaction represents a new route for the synthesis of stereodefined alpha-halomethylene-gamma-butyrolactones, lactams, tetrahydrofurans, and cyclopentanes. A mechanism involving a neighboring coordination group is proposed to explain the experiment results.     

Hydroxyl-directed cyclizations of 1,6-enynes

The palladium-catalyzed, hydroxyl-directed cyclization reactions of 1,6-enynes provide a highly diastereoselective process for the syntheses of stereochemically defined cyclopentanes. Consistently high levels of cis-selectivity are possible using homopropargyl alcohols in contrast to the corresponding propargyl alcohols. Hydroborylative enyne cyclizations coupled with this directing group effect provide a useful method for the syntheses of multifaceted compounds bearing all carbon quaternary centers.     

Highly enantioselective spiro cyclization of 1,6-enynes catalyzed by cationic skewphos rhodium(I) complex

A cationic rhodium(I) complex having a skewphos ligand is shown to be a highly enantioselective catalyst for asymmetric carbocyclization of 1,6-enynes with tri-substituted olefins to control quaternary stereogenic centers of spiro-rings.     

Platinum-catalyzed cycloisomerization of 1,4-enynes via 1,2-alkenyl rearrangement

The cycloisomerization of 1,4-enyne 1 in the presence of platinum(II) catalyst afforded 1,2,3-trisubstituted 1H-indene 2 and 2' in good to excellent yields. The reaction proceeded through an unprecedented 1,2-alkenyl rearrangement that afforded a novel reaction topology of 1,4-enynes.     

Gold(I) complexes bearing P-pyrrole phosphine ligands: Synthesis and catalytic activity towards cycloisomerization of 1,6-enynes

P-pyrrole phosphines (R₂Ppyr), in which a pyrrole group is directly bonded to the phosphorus atom, act as monodentate k-P ligands towards gold(I) center to afford either neutral or cationic mononuclear complexes as well as neutral dinuclear complexes. All of these new gold(I) complexes have been structurally characterized and their first uses in catalysis have demonstrated their effectiveness as precatalysts for the enyne cycloisomerization reactions.     

A DFT-based analysis of the gold-catalyzed cycloisomerization of 1-siloxy 1,5-enynes to cyclohexadienes

In this work, we present a deep theoretical study on the intriguing and unexpected gold-catalyzed cycloisomerization of siloxy enynes to cyclohexadienes. To this end, we have evaluated the electronic and steric properties for three types of alkynyl substituents along the reaction paths and the implications on the evolution through divergent, competitive pathways. For an alkynyl -OR substituent, the results strongly suggest a polarization of the π electrons along the delocalized C2-C1-O system in the key cyclopropyl-carbene intermediate, which is enhanced by the bulkiness of the R group. The results reproduce the experimental observations in excellent agreement and provide interesting and useful clues for predicting the effects of the alkynyl substituent on the nature of the key intermediate and, hence, on the reactivity mode and selectivity.