Oligomerization catalysts. III. Cyclocodimerization of conjugated dienes with acetylenic hydrocarbons catalyzed by iron(0) complexes. Synthesis of 1,2-diphenyl-1,4-cyclohexadiene

Carbonaro, A.; Greco, A.; Dall'Asta, G.

doi:10.1021/jo01274a061

Cited by 65 publications

(14 citation statements)

References 3 publications

(4 reference statements)

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“…The remarkable versatility of the Diels−Alder reaction for the stereospecific construction of six-membered rings has made this reaction one of the most widely studied methods in organic chemistry. − The severity of the reaction conditions required for a purely thermal [4 + 2] cycloaddition depends on the substituents on the diene and dienophile. Various modifications have been developed to enhance the rate of the cycloaddition and to the improve selectivities including: the use of high pressure, ultrasound, Brönsted acids, traditional Lewis acids, 158c,, special solvent effects, molecular sieves, adsorption on chromatography adsorbents, in situ radical formation, and the use of transition metals. − The past 10 years has seen a tremendous increase in the development of useful transition metal catalysts which promote the reaction. This interest stems from the mild reaction conditions and the ability to modify the chemo- and regioselectivities as the metal and ligand are varied.…”

Section: 8 [44 π + 22 π] Cycloadditionsmentioning

confidence: 99%

“…Two main classes of metal-catalyzed Diels−Alder reactions can be identified. The metal either serves as a Lewis acid and complexes to a carbonyl or other polarized group 169,170 or the metal complexes to the π-bonds of alkene or alkyne and the diene. − A brief review of recent results using Lewis acids will be presented in order to compare the state of the art with emerging olefin complexing reactions.…”

Section: 8 [44 π + 22 π] Cycloadditionsmentioning

confidence: 99%

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Transition Metal-Mediated Cycloaddition Reactions

1996

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Contents 1. Introduction 49 2. Three-Membered Ring Formation 50 2.1. [2 + 1] Cycloadditions Using Stoichiometric Amounts of Zinc Carbenoids (Simmons−Smith Type) 50 2.2. [2 + 1] Cycloadditions with Stoichiometric Amounts of Samarium Carbenoids 52 2.3. [2 + 1] Cycloadditions with Transition Metal-Stabilized Alkyl Carbenes of Cu, Pd, Ni, Co, and Rh 52 2.4. Cyclopropanations with Metal Carbenes Derived from R-Diazocarbonyl Compounds 54 2.5. [2 + 1] Cycloadditions with Vinylcarbenes 54 2.6. [2 + 1] Cycloadditions with Palladium Complexes of Oxatrimethylenemethane 56 2.7. Transition Metal-Catalyzed Aziridinations 57 3. Four-Membered Ring Formation 58 3.1. [2 2π + 2 2π ] Cycloadditions of Strained Alkenes with Electron-Deficient Olefins 58 3.2. [2 2π + 2 2π ] Cycloadditions of Strained Alkenes with Acetylenes 59 3.3. Intramolecular [2 2π + 2 2π ] Cycloadditions 60 4. Five-Membered Ring Formation 60 4.1. [3 2σ + 2 2π ] Cycloadditions with Metallacyclobutanes 60 4.2. [3 2σ + 2 2π ] Cycloadditions with Pd−Trimethylenemethane Complexes 61 4.3. Intramolecular [3 2σ + 2 2π ] Cycloadditions with Pd−TMM Complexes 62 4.4. [3 2σ + 2 2π ] Cycloadditions with Methylenecyclopropane 64 4.5. Intramolecular [3 2σ + 2 2π ] Cycloadditions with Methylenecyclopropanes 66 4.6. [3 4π + 2 2π ] Cycloadditions with Metal Carbenoids 67 4.7. [4 4π + 1 2π ] Cycloadditions 69 5. Six-Membered Ring Formation 69 5.1. [2 2π + 2 2π + 2 2π ] Cycloadditions 69 5.2. Acetylene [2 2π + 2 2π + 2 2π ] Cyclotrimerization Reactions 70 5.3. Acetylene−Olefin [2 2π + 2 2π + 2 2π ] Cyclotrimerizations 71 5.4. Hetero [2 2π + 2 2π + 2 2π ] Cyclotrimerizations 72 5.5. Homo-Diels−Alder [2 2π + 2 2π + 2 2π ] Cycloadditions 72 5.6. Bis-Homo-Diels−Alder [2 2π + 2 2π + 2 2π ] Cycloadditions 74 5.7. [3 2π + 3 2σ ] Cycloadditions 74 5.8. [4 4π + 2 2π ] Cycloadditions 75 6. Seven-Membered Ring Formation 78 6.1. [4 4π + 3 2σ ] Cycloadditions 78 6.2. [5 2π+2σ + 2 2π ] Cycloadditions 79 7. Eight-Membered Ring Formation 79 7.1. [2 2π + 2 2π + 2 2π + 2 2π ] Cycloadditions 80 7.2. [4 4π + 2 2π + 2 2π ] Cycloadditions 80 7.3. [4 4π + 4 4π ] Cycloadditions 81 7.4. [6 6π + 2 2π ] Cycloadditions 83 8. Ten-Membered Ring Formation 85 9. Conclusion and Remarks 87 49

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Section: 8 [44 π + 22 π] Cycloadditionsmentioning

confidence: 99%

Section: 8 [44 π + 22 π] Cycloadditionsmentioning

confidence: 99%

Transition Metal-Mediated Cycloaddition Reactions

1996

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“…Cyclooctatetraene (COT, C 8 H 8 ) forms numerous complexes, both mononuclear and polynuclear, with the d- and f-block elements, in which it displays a variety of bonding modes depending, in part, on the number of π-electrons that it contributes. , The fluxional behavior of COT complexes, especially of the metal tricarbonyls M(CO) 3 ((1−4-η)-C 8 H 8 ) (M = Fe, Ru, Os) and M(CO) 3 ((1−6-η)-C 8 H 8 ) (M = Cr, Mo, W), has played an important role in the study of nonrigidity in organometallic molecules. , In the case of iron, a bis(cyclooctatetraene) complex, Fe((1−6-η)-C 8 H 8 )((1−4-η)-C 8 H 8 ) ( 1 ), has been isolated by reduction of FeCl 3 or Fe(acac) 3 in the presence of COT with an excess of isopropylmagnesium bromide 6,7 or, better, triethylaluminum. , Although the hapticity of the COT rings in 1 has been confirmed by single-crystal X-ray structural analysis, , in solution at room temperature the compound shows just a singlet in its 1 H and 13 C NMR spectra, indicating that the rings are equivalent on the NMR time scale. On cooling to −84 °C, a limiting spectrum is observed for the η 6 -ring but the resonance for the η 4 -ring remains a sharp singlet. , Complex 1 also catalyzes a variety of oligomerization reactions of alkenes and alkynes. ,, In view of the current interest in the organometallic chemistry and catalytic properties of zero valent ruthenium complexes containing arenes and polyenes as the only ligands, such as Ru((1−6-η)-1,3,5-C 8 H 10 )(η 4 -1,5-C 8 H 12 ) − and Ru(η 6 -C 10 H 8 )(η 4 -1,5-C 8 H 12 ), , it is surprising that the ruthenium analogue of 1 is apparently unknown. We describe here the synthesis of Ru((1−6-η)-C 8 H 8 )((1−4-η)-C 8 H 8 ) ( 2 ) and some of its derivatives, together with a study of their fluxional behavior.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Structure, and Fluxional Behavior of Bis(cyclooctatetraene)ruthenium(0) and Its Derivatives

Bennett¹,

Neumann²,

Willis³

et al. 1997

Organometallics

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The complex Ru((1−6η)-C8H8)((1−4-η)-C8H8) (2), which is made in two steps from Ru(acac)3, shows three fluxional processes: (1) equilibration of the protons and carbon atoms of the (1−4-η)-C8H8 ring, which appear as a singlet even at −100 °C; (2) role reversal (exchange of hapticity) of the two rings; (3) a 1,5-shift within the (1−6-η)-C8H8 ring. Processes 2 and 3 cause the 1H and 13C resonances of C8H8 to appear as a broad singlet at room temperature, though the (1−6-η)-ring is static at ca. −60 °C. The free energies of activation ΔG ⧧ 235 for processes 2 and 3 have been estimated from magnetization transfer experiments to be 12.8 ± 0.2 and 13.5 ± 0.2 kcal mol-1, respectively. Complex 2 reacts with ligands L to give adducts Ru(L)((1−4-η)-C8H8)((1,2,5,6-η)-C8H8) (L = CO (4), CN-t-Bu (5), P(OMe)3 (6), PMe3 (7), and PEt3 (8)). The (1,2,5,6-η)-rings in these compounds are static at room temperature and do not exchange with the fluxional (1−4-η)-C8H8 rings. The (1−4-η)-C8H8 ring in 4 undergoes the usual 1,2-shift, the free energy of activation ΔG ⧧ 259 of 13.7 ± 0.1 kcal mol-1 being considerably higher than that of 2 or of Ru(CO)3((1−4-η)-C8H8). The X-ray structures of 2, 4, 5, and 7 are reported.

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“…[1] Only after the discovery of the remarkable catalytic effect of various transition-metal complexes could the synthetic potential of this transformation be exploited. [2][3][4] Such cycloadditions of dienynes A are assumed to proceed via metallacyclic intermediates of type B and C, which are formed by oxidative cyclization, and subsequent insertion of the alkyne (Scheme 1). [3] We speculated, however, that entirely different scenarios might also result in a net [4+2] cycloaddition, and present herein preliminary data to support this view.…”

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confidence: 99%

Two Manifolds for Metal‐Catalyzed Intramolecular Diels–Alder Reactions of Unactivated Alkynes

Fürstner

Stimson

2007

Angewandte Chemie

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The poor reactivity of unactivated alkynes as dienophiles has for a long time limited their use in Diels-Alder reactions. [1] Only after the discovery of the remarkable catalytic effect of various transition-metal complexes could the synthetic potential of this transformation be exploited.[2-4] Such cycloadditions of dienynes A are assumed to proceed via metallacyclic intermediates of type B and C, which are formed by oxidative cyclization, and subsequent insertion of the alkyne (Scheme 1).[3] We speculated, however, that entirely different scenarios might also result in a net [4+2] cycloaddition, and present herein preliminary data to support this view.Activation of the triple bond of A followed by attack of the dienes proximal alkene moiety should generate an electrophilic metal carbene F with a pendant vinyl group on its cyclopropyl ring.[5] This species might undergo a "metallaCope" rearrangement with formation of C and proceed from there on; alternatively, one may envisage formation of cation G that releases cycloadduct D and regenerates the catalyst. The excellent performance of cationic gold complexes as carbophilic Lewis acids [5] prompted us to probe this concept by exposing various dienynes to [(Ph 3 P)Au]SbF 6 generated in situ (Table 1). Whereas the parent compounds 1 decomposed (Table 1, entry 1), substrates with a nonterminal alkyne were converted into the corresponding 1,4-cyclohexadiene products in respectable yields. As silyl end groups on the alkyne are lost upon work-up, [6] access to the unfunctionalized cycloadducts is secured (Table 1, entries 2-6).The proposed mechanism, which proceeds via an intermediate of type F, is consistent with the results shown in Scheme 2. Thus, compound 10 furnished cycloadduct 12 (68 %) and tetrahydrofuran 13 (15 %), which derives from the putative electrophilic carbene 11 by reaction with the tethered alcohol; such vinylogous alkoxycyclizations have ample precedence in gold and platinum catalysis.[7] Even more instructive is the conversion of substrate 14 into 16 and 18, both of which again likely originate from the same intermediate 15. Whereas evolution of this species along the pathway depicted in Scheme 1 affords cycloadduct 16, competing attack of the phenyl ring onto the electrophilic carbene provides the companion product 18. The latter course corroborates the view that gold cyclopropyl "carbenes" [c] The product is partly aromatized in air (ca. 10 %). Ts = toluene-4-sulfonyl.

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Oligomerization catalysts. III. Cyclocodimerization of conjugated dienes with acetylenic hydrocarbons catalyzed by iron(0) complexes. Synthesis of 1,2-diphenyl-1,4-cyclohexadiene

Cited by 65 publications

References 3 publications

Transition Metal-Mediated Cycloaddition Reactions

Transition Metal-Mediated Cycloaddition Reactions

Synthesis, Structure, and Fluxional Behavior of Bis(cyclooctatetraene)ruthenium(0) and Its Derivatives

Two Manifolds for Metal‐Catalyzed Intramolecular Diels–Alder Reactions of Unactivated Alkynes

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