Alkenes Allene

The dienoplules for reaction with butadiene can be alkenes, allenes, and alkynes. Simple alkenes like ethylene are poor dienoplules resulting in sluggish reactions. Substituted olefins, X—C=C—X, are more reactive when X and/or X are C=C, Ar, COOR, COOH, COH, COR, COCl, CN,... 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

Such reactions involve the addition of organometallic reagent to unsaturated systems like alkynes, alkenes, allenes, or related structures in order to create a new C-C bond and C-M bond at the same time. The C-M bond can then be functionalized by an electrophile to generate a wide range of products. 

We initially observed an addition reaction of tertiary phosphines to unactivated alkynes. The method was then applied to reactive alkenes, allenes and 1,3-dienes, and finally to unactivated alkenes (Scheme 4). Such a step-up methodology turned out to be effective in this study. 

A number of ex situ spectroscopic techniques, multinuclear NMR, IR, EXAFS, UV-vis, have contributed to rationalise the overall mechanism of the copolymerisation as well as specific aspects related to the nature of the unsaturated monomer (ethene, 1-alkenes, vinyl aromatics, cyclic alkenes, allenes). Valuable information on the initiation, propagation and termination steps has been provided by end-group analysis of the polyketone products, by labelling experiments of the catalyst precursors and solvents either with deuterated compounds or with easily identifiable functional groups, by X-ray diffraction analysis of precursors, model compounds and products, and by kinetic and thermodynamic studies of model reactions. The structure of some catalysis resting states and several catalyst deactivation paths have been traced. There is little doubt, however, that the most spectacular mechanistic breakthroughs have been obtained from in situ spectroscopic studies. 

Thermal and photochemical cycloaddition reactions of 27r-electron species represent an important synthetic approach to four-membered rings. The reactions summarized in this section include 2 + 2 cycloaddition reactions of thioketones, thioketenes, isothiocyanates, sulfenes and iminosulfenes with alkenes, allenes, ketenes, ketenimines and alkynes. 

Perfluorination of unsaturated hydrocarbons such as alkenes, allenes (Fig. 7) [53] and aromatics (Fig. 8) [54,55] is also possible since the total energy released upon fluorine addition to a carbon-carbon double bond (typically between 251.4-292.9 kjmol-1) is not sufficient to break carbon-carbon single bonds. 

Oxidation of organic compounds by ruthenium tetraoxide has been reviewed. The oxidation of various types of organic compounds such as alkanes, alkenes, allenes, aromatic rings, alcohols, amines, and sulfides has been discussed The cyclic oxoruthe-nium(VI) diesters that are formed in the initial step of the oxidation of alkenes are considered to be intermediates in the formation of 1,2-diols.70 The development of new and selective oxidative transformations under ruthenium tetroxide catalysis during the past 10 years has been reviewed. The state of research in this field is summarized and a systematic overview of the reactivity and the reaction mode of ruthenium tetroxide is given.71... 

Billups reported the cycloaddition of benzocyclopropene 163 to 1,3-butadiene (Scheme 2.44). The reaction proceeded at 0°C with only 1 mol% of AgBF4 to afford product 165 in 64% yield.76 Under these conditions, compound 163 also reacted in a [3+2] fashion with alkenes, allenes, and disubstituted alkynes but in much lower yields (11-25%) of [3+2] cycloaddition products. A phenylsilver species has been invoked as an intermediate. The reaction probably proceeds through a cationic mechanism. 

Heterocyclization reactions with saturated moieties (alcohols, amines, thiols, etc.) or acids on unsaturated counterparts (alkenes, allenes, alkynes, etc.) are not covered in this chapter since they are addition, and not isomerization, reactions. Silver is also widely used as an activating agent for producing highly reactive metallic cations (anion metathesis), which, in turn, may catalyze cycloisomerization reactions. This aspect is covered only when the silver control experiments give substantial positive results. 

A. Krebs, J. Swienty-Busch, Eliminations to Form Alkenes, Allenes and Alkynes and Related Reactions, in Comprehensive Organic Synthesis (B. M. Trost, I. Fleming, Eds.), Vol. 6, 949, Pergamon Press, Oxford, 1991. 

Applications of organomercuiy compounds in synthesis overwhelmingly concern Markovnikov conversion of alkenes, allenes and cyclopropanes to alcohols, ethers, amines, peroxides and azides by... 

Of Alkenes, Allenes, Alkyncs, and Other Unsaturated Systems... 

TT-Bonded ligands can be closed shell, 2n electron donors (n = 1 — 3) such as alkenes, allenes, alkynes, arenes, and polyenes these have been termed even polyene ligands. They may also be open shell, odd polyene ligands such as allyl, pentadienyl, cyclopropenyl, and cyclopentadienyl, which are formally viewed as anionic hgands, donating 2n electrons (n = 1 - 3). 

Examples of compounds with a Sn-Sb bond" are (Me3Sn)2Sb-Sb(SnMe3)2 (46) and (Me3Sn)3Sb (47) photolysis of (46) provides (47). IR spectra of (Me3Sn)3E (E = P, As, or Sb) indicate planar [SnsE] cores. The Sn-P, Sn-As, and Sn-Sb bonds are thermally relatively stable, but are oxygen and water sensitive. Tin-phosphorus bonded compounds add to heterocumulenes (as do Sn-N bonded compounds), and to alkenes, allenes, and alkynes such as CH2=CHCH2C1, CH2=CHPh and PhC=CH (unlike Sn-N bonded species) (equation 90). 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated... 

Eliminations to Form Alkenes, Allenes and Alkynes and Related Reactions... 

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