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We report a rhodium(I)‐catalyzed asymmetric cyclohydroformylation reaction of 1,6‐enynes with formaldehyde. The reaction of 1,6‐enynes with formaldehyde in the presence of a cationic Rh(I) catalyst, such as [Rh(cod)2]+OTf−, and a chiral biaryl diphosphine led to asymmetric cyclohydroformylation to produce aldehydes with higher‐order structures highly enantioselectively. This transformation procedure is applicable to a variety of enynes, with wide compatibility in various atoms liking between the alkyne and alkene parts, substituents at the alkyne terminus, and substituents at the alkene part, being converted to newly formed aldehydes in 14% to 90% yields with 50% to 98% ee. The products were further transformed with various nucleophiles to alcohols, an amine, and a diene without loss of chirality at their γ‐position. [ABSTRACT FROM AUTHOR]

Efficient four- and five-step routes to access functionalized bicyclo[3.2.1]oct-2-ene and bicyclo[3.3.1]nonadiene via indium-mediated cycloisomerization of 1,6-enynes has been developed. This atom-economical catalytic process was optimized and relied on the efficiency of InCl3 leading to the preparation of functionalized bicyclic adducts in up to 99% isolated yield. The cyclization occurred on two different processes (5-exo versus 6-endo pathway) and were influenced by the substitution of the alkynyl moiety. The exo process was favored for non-substituted alkynes whereas the endo pathway was generally observed for substituted alkynes. Then, the presence of electron-withdrawing groups on the aryl substituted alkyne increased the ratio of the exo isomer. DFT calculations were performed on stability of intermediates and corroborated the intervention of InCl3.

A full account of our efforts toward an asymmetric redox bicycloisomerization reaction is presented in this article. Cyclopentadienylruthenium (CpRu) complexes containing tethered chiral sulfoxides were synthesized via an oxidative [3 + 2] cycloaddition reaction between an alkyne and an allylruthenium complex. Sulfoxide complex 1 containing a p-anisole moiety on its sulfoxide proved to be the most efficient and selective catalyst for the asymmetric redox bicycloisomerization of 1,6- and 1,7-enynes. This complex was used to synthesize a broad array of [3.1.0] and [4.1.0] bicycles. Sulfonamide- and phosphoramidate-containing products could be deprotected under reducing conditions. Catalysis performed with enantiomerically enriched propargyl alcohols revealed a matched/mismatched effect that was strongly dependent on the nature of the solvent.

A cationic Pd(II)-catalyzed redox neutral arylative cyclization of enynes by using β-acetoxy elimination as the quenching step has been developed. The reaction offers an efficient method to access a variety of carbocycles and N -heterocycles bearing an exocyclic double bond. [ABSTRACT FROM AUTHOR]

The solvent effect on the reaction mechanism of the Pd( II)-catalyzed cycloisomerization of 4-aza-1-cyclopropyl-1,6-enyne toward 3-aza-bicyclo[4.1.0]heptene and homo-ene product was investigated via density functional theory. Four different Pd complexes, PdCl2 {P( OPh)3}, PdCl2 ( PPh3 ), Pd{P( OPh)3}, and Pd( PPh3 ) as hypothetical active catalyst species were applied to ( E)- N-(but-2-ynyl)- N-(3-cyclopropylallyl)amine model substrate in 1,4-dioxane and dichloroethane solvent environment. Reaction pathways toward ( Z)-3-(( Z)-buta-1,3-dien-1-yl)-4-ethylidenepyrrolidine (homo-ene product) and 7-cyclopropyl-6-methyl-3-azabicyclo[4.1.0]hept-4-ene were obtained and energetic differences were compared. The selective formation of 3-aza-bicyclo[4.1.0]heptenes in toluene at 130°C that was not reproduced in other solvents at lower temperatures was likely because of the catalyst effect rather than the solvent effect. [ABSTRACT FROM AUTHOR]

Abstract: Silver-catalyzed cycloisomerizations of 1,6-enynes derived from propiolamides led to a selective formation of Alder-ene type 1,4-dienes. Interestingly, AgNTf2 outperformed gold or platinum catalysts in terms of selectivity and reactivity, providing the 1,4-dienes at room temperature. The presence of C(5) carbonyl group in combination with Ag salts is key to the selectivity and the β-oxo coordinated silver carbenoids were proposed as an intermediate based on the reaction profiles. [Copyright &y& Elsevier]

Abstract: A domino sequence of cyclization of 1,6-enyne with 2-bromoarylaldehyde followed by the intramolecular Aldol-condensation has been realized in the presence of 5mol% of palladium catalyst. This sequence provides a convenient protocol to access polycyclic ring systems with readily available starting materials under simple Pd(0)-catalyzed conditions. The intramolecular Aldol-condensation has been proposed as the key step for the catalytic cycle. [Copyright &y& Elsevier]

Abstract: In the present work, the density functional theory is employed to study qualitatively the mechanism of the rearrangement reaction of 1,6-enynes catalyzed by PtCl2 in gas phase. An efficient and reliable strategy has been adopted to search for the transition states of the reaction involved. As demonstrated, the rearrangement reaction process mainly involves two possible regioalternative mechanisms: cycloisomerization and the formation of cyclopropanes. Four reaction paths for the mechanism of cycloisomerization and one reaction path for the formation of cyclopropanes are investigated at the levels of B3LYP/LANL2DZ* and B3LYP/LANL2MB. The results of calculations show that the rate-determining step for the cycloisomerization is the hydrogen transfer from Pt to C7, and the rate-determining step for the formation of cyclopropanes is the formation of 3-member ring involving C6 and C7. This conclusion is different from the mechanism conjectured by Echavarren. According to our calculations, the result obtained is in agreement with the experiment. The coordination of Pt with the unsaturated bonds releases a large amount of heat, which provides the thermodynamical driving force for the reaction. [Copyright &y& Elsevier]

Efficient four- and five-step routes to access functionalized bicyclo[3.2.1]oct-2-ene and bicyclo[3.3.1]nonadiene via indium-mediated cycloisomerization of 1,6-enynes has been developed. This atom-economical catalytic process was optimized and relied on the efficiency of InCl3 leading to the preparation of functionalized bicyclic adducts in up to 99% isolated yield. The cyclization occurred on two different processes (5-exo versus 6-endo pathway) and were influenced by the substitution of the alkynyl moiety. The exo process was favored for non-substituted alkynes whereas the endo pathway was generally observed for substituted alkynes. Then, the presence of electron-withdrawing groups on the aryl substituted alkyne increased the ratio of the exo isomer. DFT calculations were performed on stability of intermediates and corroborated the intervention of InCl3. [ABSTRACT FROM AUTHOR]

A novel and straightforward palladium-catalyzed desymmetric [2+2+2] cycloaddition reaction of alkyne-tethered cyclohexadienone and internal alkyne is established. Widely existing fused tricyclic hydronaphthofuran and hydronaphthopyrrole frameworks are prepared diastereoselectively in moderate to excellent yields. One-step aromatization process provides a new and facile access to important benzene-containing tricycles from above cycloaddition products. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: A variety of 1,6-enynes were synthesized by an Ugi-reaction and further elaborated by a PdII/IV catalyzed oxidative cyclization to produce N-substituted 3-aza-bicyclo[3.1.0]hexan-2-ones. Different substitution patterns were tested to examine the scope and limitations of the amide tethered substrates. [Copyright &y& Elsevier]

A full account of our efforts toward an asymmetric redox bicycloisomerization reaction is presented in this article. Cyclopentadienylruthenium (CpRu) complexes containing tethered chiral sulfoxides were synthesized via an oxidative [3 + 2] cycloaddition reaction between an alkyne and an allylruthenium complex. Sulfoxide complex 1 containing a p-anisole moiety on its sulfoxide proved to be the most efficient and selective catalyst for the asymmetric redox bicycloisomerization of 1,6- and 1,7-enynes. This complex was used to synthesize a broad array of [3.1.0] and [4.1.0] bicycles. Sulfonamide- and phosphoramidate-containing products could be deprotected under reducing conditions. Catalysis performed with enantiomerically enriched propargyl alcohols revealed a matched/mismatched effect that was strongly dependent on the nature of the solvent.