Alkene also

The cross-coupling of two alkenes also takes place. Alkenes such as acrylate react regioselectively with 1,3-dimethyluracil (290) to afford 5-(l-alkenyl)ura-cils such as 291 in a high yield[260]. 

The facile cyclopalladation of allylamine proceeds due to a chelating effect of the nitrogen. In MeOH, methoxypalladation take.s place to give the five-mem-bered chelating complex 507[460). The CO Insertion takes place readily in EtOH, giving ethyl 3-methoxy-4-dimethylaminobutyrate (508) in 50% yield[461). The insertion of alkenes also proceeds smoothly, giving the ami-noalkenes 509[462],... 

Reaction of triethylsilyl hydrotrfoxide with electron-rich olefins to gh/e dioxetanes that react IntrarTMlecularly with a keto group in the presence of t-txrtyidimethyl silyl triflateto afford 1,2,4 Inoxanes also oxydatnre cleavage ol alkenes Also used in cleavage ol olefins... 

Alkenes — Also known as olefins, and denoted as C H2 the compounds are unsaturated hydrocarbons with a single carbon-to-carbon double bond per molecule. The alkenes are very similar to the alkanes in boiling point, specific gravity, and other physical characteristics. Like alkanes, alkenes are at most only weakly polar. Alkenes are insoluble in water but quite soluble in nonpolar solvents like benzene. Because alkenes are mostly insoluble liquids that are lighter than water and flammable as well, water is not used to suppress fires involving these materials. Because of the double bond, alkenes are more reactive than alkanes. 

The hydrofluonnation of alkenes also occurs in the gas phase, generally at somewhat higher temperatures [J]. Huoroethane is obtained m yields as high as 98% at 100 to 160 C by reaction in the presence of minor amounts of higher ot-olefms [6], and 2-fluoropropane is prepared in greater than 90% yield at <.80 "C from hydrogen fluonde and propene in the presence of activated carbon [7]... 

Alkenes also form a homologous series as the carbon number increases, the number of possible isomeric structures for each member increases more rapidly than in the case of the alkane series. 

Stannylation of lithiated alkenes also provides allylstannanes11 13. 

Dipolar addition to alkenes also occurs with species other than ozone, often to give products much more stable than the labile molozonides (54), e.g. addition of azides (61) to give dihydrotriazoles (62) ... 

Alkenals also add to simple olefins to yield oxetanes, Eq. 43. Using acetaldehyde and the isomeric 2-butenes the quantum yield is low, and... 

For the experiment of Figure 11.1 the degree of syngas conversion was kept at a low level, 0.2-0.3, so that the partial pressures of 1-alkenes also remained low. 

The development of chiral hydrogenation catalysts for unfunctionalized alkenes also allows enantioselective hydrogenation of functionalized olefins where the functionality in the molecule is remote from the double bond. A series of oxazoline-, imidazoline- and pyridine-derived catalysts have been screened for the hydrogenation of unsaturated derivatives of vitamin E (Scheme 30.3). Hy-... 

The oxidative cyclization of vinylallenes need not be directed by a pendant hydroxyl group in order to succeed. The higher reactivity of the allene compared with the exocyclic methylene group in 73 (Eq. 13.23) with monoperphthalic acid leads primarily to the allene oxide which rearranges to cydopentenone 74 [27]. Inevitably some epoxidation of the alkene also takes place during the reaction. When m-CPBA is used as the oxidant, another side reaction is associated with m-chlorobenzoic add-mediated decomposition of the intermediate epoxide. It is possible to overcome this problem by performing the epoxidation in dichloromethane in a two-phase system with aqueous bicarbonate so as to buffer the add [28]. 

Substrates with carbamate-protected [81, 82] and even free hydroxyl groups [69] reacted similarly in a deprotonation-reprotonation sequence, the latter even with retention of the -configuration of an alkene such as 46 (Scheme 1.19). The analogous (E)-alkene also delivers only E-product. 

In a similar manner, polymers with unsaturated chains or side chains can be converted to polyamines [66-69]. Conjugated diolefins usually undergo hydroformylation with low selectivities [70]. Mostly hydrogenation of at least one double bond occurs and mixtures of various saturated and unsaturated amines and diamines are obtained [71]. Similar to alkenes also alkynes may serve as unsaturated compounds in hydro aminomethylation reaction sequences. Although synthetically attractive, only a few investigations towards hydroformylation and hydroaminomethylation of alkynes in the presence of N-nuclcophilcs are known. Usually a preferred transformation to furanonic derivatives is observed under hydroformylation conditions [27]. 

The perruthenate oxidation of alcohols has been incorporated into a one-pot conversion of alkenes into carbonyl compounds via their initial hydroboration [44], Overall yields can be as high as 98%. Where the initial alkene also contains carbonyl groups these are reduced in the first step and are reoxidized by the perruthenate. 

In 1994, Thomas reported146,147 that alkenes also underwent an addition reaction with vinylketene complexes that differed crucially in the loss of the ketene carbonyl fragment. Complexes 252.a-252.d were isolated as yellow crystalline solids. Clearly this suggests that the process occurs by a mechanism different from the alkyne insertion, and this will be discussed... 

Alkoxides and imido are used as anionic ligands in zirconium and titanium catalysts for the polymerisation of alkenes, sometimes as the only anions, but often in combination with cyclopentadienyl ligands. Imides linked to cyclopentadienyl groups form part of the single-site catalyst developed by Dow (Chapter 10) (Figure 1.9, 1). In very different titanium catalysts, namely those used for epoxidation of alkenes, also alkoxide ligands are used (Chapter 14). 

Alkenes (also called olefins). These constituents are characterized by the presence of branched or unbranched chains of carbon atoms. Alkenes are not generally found in crude oil but are common in refined products, such as naphtha (a precursor to gasoline). Common gaseous alkenes include ethylene (CH2=CH2) and propene (also called propylene, CH3CH=CH2). 

Recent experimental (a) and theoretical (b) studies involving sterically encumbered alkenes also suggest that the spiro TS is favored over a planar one ... 

Cycloadditions to racemic mixmres of chiral alkenes also show that there is virtually no induction from the nitrile oxide part, meaning that there is no effect of matching-mismatching of the partners in the transition state. In the reaction with glyceraldehyde, and threose- and glucose-derived nitrile oxides, only the usual ... 

Of course, a close stmctural relationship between radical cations and parent molecules is not likely to hold generally, but it is a fair approximation for alternant hydrocarbons. Deviations have been noted some stilbene radical cations have higher-lying excited states without precedent in the PE spectrum of the parent for radical cations of cross-conjugated systems (e.g., 1) already the first excited state is without such precedent. These states have been called non-Koop-manns states. Alkenes also feature major differences between parent and radical cation electronic structures. 

The addition of singlet oxygen to alkenes also gives dioxetanes. A number of mechanisms have been proposed and the literature abounds with theoretical and experimental results supporting one or more possible intermediates (a) 1,4-diradicals, (b) 1,4-dipolar, (c) perepoxides, or (d) concerted (Scheme 95). Both ab initio and semi-empirical calculations have been done and to date the controversy is still not resolved. These mechanisms have been reviewed extensively (77AHC(21)437, 80JA439, 81MI51500 and references therein) and will not be discussed here, except to point out that any one mechanism does not satisfactorily account for the stereospecificity, solvent effects, isotope effects and trapped intermediates observed. The reaction is undoubtedly substrate-dependent and what holds for one system does not always hold for another. 

Alkenes — Also known as olefins, and denoted as CuH2u the compounds are unsaturated hydrocarbons widr a single carbon-to-carbon double bond per molecule. The alkenes are very similar to the alkanes in boiling point, specific gravity, and other physical characteristics. Like alkanes, alkenes are at most only weakly polar. 

The cycloaddition of an enone with electron-rich alkenes also proceeds with remarkable regioselectivity. The rationalization is that in the excited state, polarization of the enone double bond is opposite in direction as compared with the ground state [190], In other words, photochemical excitation induces contrapolarization. With this consideration the head-to-head dimerization generally observed is reasonable as it involves one molecule each in the ground and excited states. 

Strained alkenes also react by [2 + 2] cycloadditions (see Section 1.3.2.1.1.). A recent study on the preparation of cyclohexa-l,2,4-triene (isobenzene, 44) and the corresponding 4,5-benzo derivative 45 as short-lived transients reported the cycloaddition of these cyclic allenes.29... 

Atkenes from sic-dihaiides. The reaction of /c-dihalides with NaSeCH3 or NaSeC6H5 in ethanol or THF-HMPT (3 1) results in alkenes. The reaction involves a formal a rr-elimination in the case of wc-dibromides or uie-chloroiodidcs, but a formal xyn-elimination in the case of w c-dichlorides. Elimination to form alkenes also occurs with /K-haloalkyl phenyl selenides. 

Of the isomeric aldehydes indicated in Eq. (7.1), the linear aldehyde corresponding to anti-Markovnikov addition is always the main product. The isomeric branched aldehyde may arise from an alternative alkene insertion step to produce the [RCH(Me)Co(CO)3] or [RCH(Me)Rh(CO)(PPh3)2] complexes, which are isomeric to 2 and 8, respectively. Alternatively, hydroformylation of isomerized internal alkenes also give branched aldehydes. The ratio of the linear and branched aldehydes, called linearity, may be affected by reaction conditions, and it strongly depends on the catalyst used. Unmodified cobalt and rhodium carbonyls yield about 3-5 1 mixtures of the normal and iso products. 

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