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Cyclopen tenes

Carboxylate anions are better nucleophiles for allylation. The monoepoxide of cyclopentadiene 343 is attacked by AcOH regio- and stereoselectively via tt-aliylpalladium complex formation to give the m-3,5-disubstituted cyclopen-tene 344[212]. The attacks of both the Pd and the acetoxy anion proceed by inversion (overall retention) to give the cis product. [Pg.337]

An intramolecular variant of the Baylis-Hillman reaction is also possible, and may be used for the construction of functionalized ring systems, e.g. a cyclopen-tene derivative such as 12. However, good yields have been achieved in only a few cases ... [Pg.30]

How would you prepare the following compounds, starting with cyclopen tene and any other reagents needed ... [Pg.355]

Few racemic alkyl p-tolyl sulphoxides were prepared in rather low yields (16—40%) by the reaction of Grignard reagents with mixed anhydrides 108, 109 and compound HO formed in situ from p-toluenesulphinic acid and 3-phthalimidoxy-l,2-benzoisothiazole 1, 1-dioxide167 (equation 59). The mixed anhydrides 109 or 110 when reacted with cyclopen-tene and cyclohexene enamines 111 gave the corresponding a-ketocycloalkyl sulphoxides 112 in low yields (10-41%) along with small amounts of several by-products such as disulphides and thiosulphonates167 (equation 60). [Pg.261]

The mechanism for aldehyde-derived enamines involves a Michael-type 1,4-addition of the enamine to the alkenylcarbene complex to generate a zwit-terionic intermediate which evolves to the final product by cyclisation. On the other hand, ketone-derived enamines react through an initial 1,2-addition to the carbene carbon to generate a different zwitterionic intermediate. Then, a [l,2]-W(CO)5 shift-promoted ring closure produces a new intermediate which, after elimination of the metal moiety, furnishes the corresponding cyclopen-tene derivatives (Scheme 30). [Pg.83]

Madindoline A (7) and B (ent-8) are potent inhibitors of interleukin 6. In a total synthesis [21] that also intended to determine the relative and absolute configurations of these novel antibiotics, the densely functionalized cyclopen-tene-l,3-dione ring of 7 and 8 was elaborated via RCM of diene-diol 2 (Scheme 1). [Pg.276]

The combination of BSTP 1949 with SnCl4 converts olefins such as cyclopen-tene 1991a, cyclohexene 1991b, or cycloheptene 1991c into their trans-l,2-chloro-hydrins 1992 a-c in 74, 85 and 92% yield, respectively [168]. Reaction of the cyclic... [Pg.289]

There is no systematic study of the effect of borane reagents, and the best choice would be highly dependent on the catalysts and substrates. A series of di(alkoxy)bo-ranes have recently been synthesized and subjected to hydroboration of cyclopen-tene at ambient temperature in the presence of RhCljPPhjjj (Scheme 1-2) [18]. The... [Pg.301]

Intramolecular oxonium ylide formation is assumed to initialize the copper-catalyzed transformation of a, (3-epoxy diazomethyl ketones 341 to olefins 342 in the presence of an alcohol 333 . The reaction may be described as an intramolecular oxygen transfer from the epoxide ring to the carbenoid carbon atom, yielding a p,y-unsaturated a-ketoaldehyde which is then acetalized. A detailed reaction mechanism has been proposed. In some cases, the oxonium-ylide pathway gives rise to additional products when the reaction is catalyzed by copper powder. If, on the other hand, diazoketones of type 341 are heated in the presence of olefins (e.g. styrene, cyclohexene, cyclopen-tene, but not isopropenyl acetate or 2,3-dimethyl-2-butene) and palladium(II) acetate, intermolecular cyclopropanation rather than oxonium ylide derived chemistry takes place 334 ). [Pg.210]

Every example with a cyclohexene has proved hydrosilation to be very slow and difficult, but this difficulty was not experienced with cyclopen-tene structures by Petrov et al. (27). A number of chlorosilanes were added to bicyclo-(2,2,l)-hept-5-ene, bicyclo-(2,2, l)-hepta-2,5-diene, 2-methyl- and 2-vinylbicyclo-(2,2,l)-hept-5-ene, and dicyclopentadiene under mild conditions. Particularly surprising was the example of Eq. [Pg.425]

The cycloadditions of 1-substituted 1,2-cyclohexadienes and among them their dimerization are of interest because of the position selectivity. Does the reaction occur at the substituted or the unsubstituted ethylene subunit For that question to be answered, 1-methyl- (74), 1-phenyl- (75), 1-cyclopropyl- (76), l-(3-phenylpropyl)-(77) and l-trimethylsilyl-l,2-cyclohexadiene (79) were generated from the corresponding 1-substituted 6,6-dibromobicyclo[3.1.0]hexanes with methyllithium. Several of these dibromides are thermolabile, which particularly applies to the phenyl (93) [76] and the cydopropyl derivative [70], In those cases, it is advisable or necessary to prepare the dibromide in situ, that is, the dibromocarbene is liberated from tetrabro-momethane with methyllithium at -60 °C in the presence of the respective cyclopen-tene. Without workup, from the thus formed 6,6-dibromobicyclo[3.1.0]hexane, the 1,2-cyclohexadiene is then generated by addition of methyllithium at -30°C. [Pg.262]

Conjugated ketones and esters react with allenylsilanes to yield acylcyclopentenes (Eq. 9.60) [63]. These products are formed by initial 1,4-addition to the conjugated double bond to afford a silyl-stabilized vinyl cation intermediate. 1,2-Silyl migration gives rise to a second silyl-stabilized vinyl cation which cyclizes to the acyl cyclopen-tene (Scheme 9.14). [Pg.539]

Cyclobutene ozonide <88JST(190)125> revealed a long O—O bond of 1.492 A relative to cyclopen tene ozonide (1.475 A) <83JPC538l> and also a smaller C—O—C angle of 94.0° compared with... [Pg.585]

The cyclohexadiene derivative 130 was obtained by the co-cyclization of DMAD with strained alkenes such as norbornene catalyzed by 75[63], However, the linear 2 I adduct 131 of an alkene and DMAD was obtained selectively using bis(maleic anhydride)(norbornene)palladium (124)[64] as a catalyst ]. A similar reaction of allyl alcohol with DMAD is catalyzed by the catalyst 123 to give the linear adducts 132 and 133[66], Reaction of a vinyl ether with DMAD gives the cyclopen tene derivatives 134 and 135 as 2 1 adducts, and a cyclooctadiene derivative, although the selectivity is not high[67]. [Pg.531]

FIGURE 25. Transition structures for the epoxidation of cyclopropene, cyclobutene and cyclopen-tene with peroxyformic acid (PFA), optimized at the B3LYP/6-31+G(d,p) level of theory. The classical activation barriers are given at B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p). Dihedral angles (deviation from an ideal spiro approach (c n, is 90°) of the HO group in PFA onto the C=C bond of the alkene... [Pg.60]

TrimethylsilyOcyclopentenes.2 In the presence of TiCl4, trimcthylsilylallenes react with cyclic and acyclic a,/i- enones to form annelated (trimethylsilyl)cyclopen-tenes (equation I). The reaction is most efficient with 1-substituted (trimcthyl-... [Pg.429]

ElOb,. 530f. (1-NR2—cyclo-pentenc + 6-CF3 — 2H-pyrone) 10-Mcthoxycarbonyl-9-oxo-7-triiluoromethyl- ElOb, 530 (6-CF3- 2II-pyrone + Cyclopen tene)... [Pg.842]

For relatively unstrained medium-size rings, benzoannelation seems to exert a rather small effect on enthalpies of formation104. For example, the transformation of cyclopen-tene, cyclopentadiene and cyclohexene to indane (20, n = 5), indene and tetralin (20, n = 6) results in a change of gas-phase enthalpies of formation of (26.8 2.2), (29.1 2.6) and (31.0 2.1) kJ mol-1. For the rather strained cyclobutene, annelation to form benzocy-... [Pg.245]

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... [Pg.338]

Crimmins, M. T. Tabet, E. A. Formal total synthesis of (+)-trehazolin. Application of an asymmetric aldol-olefin metathesis approach to the synthesis of functionalized cyclopen-tenes./. Org. Chem. 2001, 66, 4012-4018. [Pg.208]

Tian et al. have reported that bis(5-pyridyl-2-methylthien-3-yl)cyclopen-tene ligand 42 shows enhancement of photochromism by complexation with a Zn2+ ion [35]. They also found that the fluorescent properties, including the intensity and emission peak wavelengths of the compound, can be reversibly regulated by UV-vis light, Zn2+, and protons [36]. [Pg.92]


See other pages where Cyclopen tenes is mentioned: [Pg.2291]    [Pg.287]    [Pg.450]    [Pg.329]    [Pg.33]    [Pg.449]    [Pg.585]    [Pg.109]    [Pg.591]    [Pg.60]    [Pg.343]    [Pg.491]    [Pg.379]    [Pg.365]    [Pg.85]    [Pg.190]    [Pg.321]    [Pg.1099]    [Pg.486]    [Pg.203]    [Pg.152]    [Pg.200]    [Pg.280]    [Pg.2344]   


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Cyclopen tenes rearrangement

Cyclopen tenes selectivity

Cyclopen tenes synthesis

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