Cycloheptene complexes

Cycloheptene complexes with gold, 12 348 Cyclohexadiene complexes with cobalt, 12 286 with group VIB metals, 12 225-227 with group VIIB metals, 12 240, 241 with iron, 12 264 with palladium, 12 313 with ruthenium, 12 278 with silver, 12 340... 

Evers, J.T.M. and Mackor, A., Photocatalysis IV. Preparation and characterization of a stable copper(I) triflate trans-cycloheptene complex. Red. Trav. Chim. Pays-Bas, 98, 423-424, 1979. 

Irradiation of cyclohexene in the presence of CuOTf produces the dimers 14 (49%) and 15 (8%), along with the cyclohexylcyclohexene 16 (24%) (Scheme 5)T The stereochemical outcome in Cu(I)-catalyzed dimerization of cyclohexene may be the result of cis-tram isomerization on irradiation of the initially formed Cu(I)-cyclohexene complex to the trans-cyclohexene-CuOTf complex 13, followed by a concerted ground state 2 + 2 cycloaddition of the highly strained tram-cyclohexene to another cyclohexene. Cycloheptene, on the other hand, produces the aU tra s-fused trimer 17 (Scheme 6) as the sole product. A 1 3 CuOTf-trans-cycloheptene complex has been proposed to be the precursor of this product. No dimerization reaction has been observed for cyclooctene and acychc olefins.However, mixed photocycloaddition occurs with cyclooctene if the other olefin is sufficiently reactive. Thus, cyclooctene adds to norbornene to produce the cyclobutane derivative 18 in 40% yield. GDdimerization was also observed when a mixture of cyclohexene and cycloheptene was irradiated in the presence of CuOTf to yield the adduct 19 (Scheme 6). ... 

It has been postulated that these cycloheptenes must be formed via a 7r-allylruthenium intermediate (Scheme 59). The cyclization is initiated by activation of the allylic C-H bond to form the 7r-allylruthenium 234. The 1-exo-dig carboruthenation of the alkynoate 234 produces the hydrido-ruthenium enolate 235. Equilibration of 235 followed by reductive elimination gives the corresponding cycloheptenes 237 and regenerates the cationic ruthenium complex. 

In another conceptually novel [5 + 2]-process, Tanino and co-workers synthesized cycloheptene derivatives by stereoselective [5 + 2]-cycloadditions involving hexacarbonyldicobalt-acetylene complexes as the five-carbon component and enol ethers as the two-carbon component (Schemes 22 and 23).60 61 The role of the dicobalthexacarbonyl complex is to facilitate formation and reaction of the propargyl cation putatively involved as an intermediate in this reaction. The dicobalthexacarbonyl moiety can be removed using various conditions (Scheme 24) to provide alkane 60, alkene 62, and anhydride 63. 

Inaba and coworkers reported that a Ti-BINOL complex is an effective catalyst for the desymmetrization of epoxide 44 using primary amines as nucleophiles. Of significant note is the efficiency of this reaction, with only 1 mol% catalyst necessary to attain high yields and selectivities [Eq. (10.11)]. Unfortunately, this epoxide is uniquely effective in this reaction. Cycloheptene oxide, dihydrofuran oxide, and an acyclic version of 44 each provided negligible yields under these reaction conditions ... 

Although the catalytic reactions described above involve mononuclear Rh and Rh complexes, dinuclear Rh compoimds have also been studied as catalyst precursors in oxygenation reactions. The system [Rh2(p.-OAc)4]/ f-BuOOH is effective in the oxidation of cyclic alkenes such as cyclopentene, cyclohexene and cycloheptene, mainly to o, /i-unsaturated ketones and allylic acetates, but with poor yields (Eq. 4) [30,31]. 

The related dirhodium(II) a-caprolactamate (cap) complex [Rh2(p--cap)4] undergoes a one-electron oxidation process at quite a lower potential (11 mV) than the acetate complex (1170 mV). In agreement with the Kochi hypothesis, the a-caprolactamate complex has recently been found to be an exceptional catalyst for the allylic oxidation of alkenes under mild conditions. A wide range of cyclohexenes, cycloheptenes, and 2-cycloheptenone (Eq. 5) are rapidly converted to enones and enediones in 1 h with only 0.1 mol % of [Rh2( x-cap)4] and yields ranging from 60 to 90%, in the presence of potassium carbonate [34]. 

However the existence of the bromine co-product is speculative and has not been experimentally verified. The reaction may be regarded as a one electron oxidation by the S i. Me , )2 aminyl radical, and it is interesting to note that aminyl radical complexes of transition metals such as [Rh(Ntrop2)(bipy)][OTf]5 (trop = 5-H-dibenzo[a,d]cycloheptene) have been isolated. The manganese and cobalt compounds were the first examples of three-coordinate Mn(lll) and Co(lll) complexes to have been structurally characterized. 

The nature of the oxidation products is traceable to the nature of the rhodium-alkene interaction. Terminal alkenes and internal ones (e.g. cycloheptene), which form 77-complexes of rhodium(I), e.g. [RhCl(alkene)2]2, are selectively converted into methyl ketones, whereas alkenes which form 7r-allylic complexes of rhodium(III) (e.g. cyclopen-tene) give alkenyl ethers via oxidative substitution of the alkene by the solvent alcohol.204... 

The only direct evidence for the presence of metal-carbene-olefin intermediates in catalytic metathesis systems comes from a study of the interaction of the tungsten cyclopentylidene complex 27 with cycloalkenes such as cycloheptene 28 in CD2CI2. When these are mixed at —96 °C and the temperature raised to between —53 and —28 °C, no polymerization occurs but the 13C NMR spectrum contains additional resonances which may be assigned to the metal-carbene-olefin complex 29. The line intensities show that the equilibrium 7 moves to the right as the temperature is lowered120. 

The complex 8W (R = Me) can also be used in a stoichiometric metathesis sequence to effect the ring closure of unsaturated ketones so as to form 1-substituted cyclopentenes, cyclohexenes and cycloheptenes in good yield, e.g. equation 24. The C=C bond reacts first to give [W]=CH(CH2)3C0(CH2)0(CH2)3Ph, which then undergoes an internal carbonyl-olefination reaction13. 

Iron carbonyls also mediate the cycloaddition reaction of allyl equivalents and dienes. In the presence of nonacarbonyldiiron a,a -dihaloketones and 1,3-dienes provide cycloheptenes (Scheme 1.5) [14,15]. Two initial dehalogenation steps afford a reactive oxoallyliron complex which undergoes a thermally allowed concerted [4 + 31-cycloaddition with 1,3-dienes. The 1,3-diene system can be incorporated in cyclic or heterocyclic systems (furans, cyclopentadienes and, less frequently, pyrroles). Noyori and coworkers applied this strategy to natural product synthesis, e.g. a-thujaplicin and P-thujaplicin [14, 16]. 

The mechanism of both the uncatalysed and W-catalysed cycloisomerisation of pent-4-yn-l-ol has been studied in detail. The endo reaction is complex but is favoured mainly as a result of stabilisation of a vinylidene intermediate <02JA4149>. The W-mediated cyclisation of alkynols has been used to synthesise glycals of the antibiotics vancosamine and saccharosamine <02OL749> and rrans-fused THP derivatives of 5 H-dibenzo[a,d]cycloheptene <02TL8697>. 

Surprisingly, some Diels-Alder cycloaddition reactions show no variation in endojexo product ratio with changes in solvent phase. Ordered liquid-crystalline solvents are not able to differentiate between endo- and exo-activated complexes in the Diels-Alder reaction of 2,5-dimethyl-3,4-diphenylcyclopentadienone with dienophiles of varying size (cyclopentene, cycloheptene, indene, and acenaphthylene), when it is carried out in isotropic (benzene), cholesteric (cholesteryl propionate), and smectic liquid-crystalline solvents at 105 °C [734]. 

Cyclization of (Z)-allylic alcohols. Cyclization of several (Z)-allylic alcohols to cyclohexenes and cycloheptenes has been observed with this complex in CH2CI2. Complexes of TiCU and 2,2,6,6-tetramethylpiperidine, VCU-CsHsNHCHs, and AlCls-CeHjNHCH, are less active than 1. 

The reaction of aryl azides with alkenes in the presence of aluminum trichloride gave different products depending on the structure and the geometry of the alkene, the reaction proceeds via the intermediacy of an aziridine 8 complexed with the Lewis acid. Thus aziridines 9 were cleanly obtained from cycloheptene and (Z)-cyclooctene, however, from cyclopentene and cyclohexene a mixture of allylic amines 10 and /5-chloro amines 11 was produced86- 87. The use of 4-chlorophenyl azide in the reaction with cyclohexene gave only a tar. 

Oxidations. A widely used method for allylic oxidation is the Kharash-Sosnovsky reaction using a peroxide and a copper(I) salt system. Enantioselective allylic oxidations of cycloalkenes such as cyclopentene, cyclohexene and cycloheptene with tert-butyl peibenzoate were investigated with a variety of catalysts derived from bis(oxazoline) ligands and copper(I) triflate complexes (eq 18). The ligand-copper(I) complexes from the /-Bu-... 

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