Alkene group

The Pd-catalyzed hydrogenolysis of vinyloxiranes with formate affords homoallyl alcohols, rather than allylic alcohols regioselectively. The reaction is stereospecific and proceeds by inversion of the stereochemistry of the C—O bond[394,395]. The stereochemistry of the products is controlled by the geometry of the alkene group in vinyloxiranes. The stereoselective formation of stereoisomers of the syn hydroxy group in 630 and the ami in 632 from the ( )-epoxide 629 and the (Z)-epoxide 631 respectively is an example. 

The intermolecular insertion of alkenes into rr-allylpalladium is unknown, except with norbomadiene(476]. On the other hand, the intramolecular insertion of alkene group in 766 into 7r-allylpalladium proceeds smoothly to give the... 

Hydrazine hydrate can often reduce vulnerable substituents on the pyrazolcme ring. One such example is the alkene group of the cyclopentenyl ring of pyrazol-3-one 16. It was found that heating 4-(l-methoxycarbonyl-2-oxopropyl)-2-cyclo-penten-l-ol 15 with hydrazine hydrate in ethanol afforded a mixture of pyrazol-3-one derivatives 16 and 17 in a 5 2 ratio (97JHC233) (Scheme 4). 

C = 0 stretching frequencies are typically lowered by about 20-30 cm 1 from the values given when the carbonyl group is conjugated with an aromatic ring or an alkene group. 

The alkene groups in TsICH = CH2]s have allowed a wider variety of chemistry to be carried out than for either TsHs or TsPhs. For example, Feher s group have prepared a variety of unsaturated POSS molecules via olefin cross-metathesis... 

An important use of the Friedel-Crafts alkylation reaction is to effect ring closure. The most common method is to heat with aluminum chloride an aromatic compound having a halogen, hydroxy, or alkene group in the proper position, as, for example, in the preparation of tetralin ... 

Peroxomonosulphate and peroxodisulphate have also been used to oxidize sulphoxides to sulphones in good yields at room temperature. Potassium persulphate (KHSO 5) readily oxidizes a range of sulphoxides to sulphones at 0 °C in yields greater than 90%, in the presence of hydroxy, keto and alkene groups . The mechanism is similar to that observed for other peroxy species, as discussed above. Peroxomonosulphate oxidation has been used as an analytical procedure for the estimation of dimethyl sulphoxide . ... 

Pyrazolopyrazolopyrazines can be prepared from a stereoselective dipolar cycloaddition between the alkene group of 284 and diazomethane (Equation 45). Ten equivalents of diazomethane are used in this reaction when only 1 equiv is used, the corresponding methyl ester of the starting material was formed <20020L773>. 

Intramolecular cyclizations of species containing two alkynes and an alkene group have been reported these take place in an aqueous basic medium and evolve heat as they progress to give isoindolium salts. In the example of 112 cyclizing to give 113, the products were not isolated but were used in subsequent intramolecular cyclizations (Equation 23 and Table 6) <2004KGS177>. 

Another piece of mechanistic evidence was reported by Snapper et al. [14], who describe a ruthenium catalyst caught in action . During studies on ring opening metathesis, these authors were able to isolate and characterize carbene 5 in which a tethered alkene group has replaced one of the phosphines originally present in Id. Control experiments have shown that compound 5 by itself is catalytically active, thus making sure that it is a true intermediate of a dissociative pathway rather than a dead-end product of a metathetic process. 

As another example, studies of the catalytic activity of the gas-phase ions [Ru-Cl(alkylidene)(diphosphane)]+ toward ring-opening olefin metathesis of norbor-nene show that an alkene group in the growing polymer chain reaches back to oc-... 

Intramolecular arylation of alkenes. The intramolecular palladium-catalyzed condensation of aryl halides with an alkene group (Heck arylation5) can actually proceed more readily than the original bimolecular version. These intramolecular cyclizations typically proceed in acetonitrile at room temperature, particularly when catalyzed by Ag2C03, which also inhibits isomerization of the double bond of the product. They can be used to obtain spiro, bridged, and fused systems. Even tetrasubstituted alkenes can participate, with formation of quaternary centers.6... 

As one might expect, the mesomeric effect of an alkoxy group enhances the activity of the C=C to attack by the carbene, but it has been noted that, where there is competition between an alkoxyvinyl group and an inactivated alkene group within the same molecule, an alkyl or aryl group stabilizes the transition state better than does the vinyloxy group (Scheme 7.10) [56]. It is noteworthy that vinyl sulphides are five times more reactive than are the enol ethers [62]. 

The Noyori reduction of various diketo esters in this series was very dependent upon the amount of add present in the reaction. Without the presence of a stoichiometric amount of add, the rate of reduction as well as the selectivity in the reduction dropped off. At higher pressures, the chemoselectivity of the reduction was poor resulting in die reduction of both alkene groups. Further, the carbonyl at C5 was never reduced under these reaction conditions but was absolutely necessary for the reduction of the C3 carbonyl. When C5 was in the alcohol oxidation state, no reduction was seen. A. Balog, unpublished results. 

The styrene/CO polymers formed with palladium complexes of diimine ligands indeed contain ester and alkene end groups [65,66,67], Slightly more ester end groups than alkene groups are formed, showing that in addition to P-hydride elimination some termination via methanolysis of acylpalladium chain ends occurs. 

Intramolecular carbon-carbon bond fomiation during reduction of a molecule possessing two activated alkene groups offers a synthetic route to cyclic structures. 

Electron transfer reduction of pyridines in both acid and alkaline solution generates the protonated radical-anion. This rapidly accepts a further electron and a proton to give a mixture of dihydropyridines. Enamine structures in these dihydro-pyridines can tautomerise to the imine, which is more readily reduced than the original pyridine molecule. Further reaction of the 1,4-dihydropyridine leads to piperidine while reduction of the t, 2-dihydropyridine leads to a tetrahydropyridine in which the alkene group cannot tautomerise to the imine and which is not therefore reduced to the piperidine stage. The reaction sequence is illustrated for 2,6-dimethyl-pyridine 18 which yields the thermodynamically favoured cis-2,6-dimethylpiperidine in which the two alkyl substituents occupy equatorial conformations. 

The ruthenium tetroxide dioxide catalytic system is effective for the oxidation of alkanols, although it will also react with any alkene groups or amine substituents that are present. The catalyst can be used in aqueous acetonitrile containing tetra-butylammonium hydroxide with platinum electrodes in an undivided cell Primary alcohols are oxidised to the aldehyde and secondary alcohols to the ketone [30]. Anodic oxidation of ruthenium dioxide generates the tetroxide, which is the effective oxidising agent. 

In many of these cases, the nucleophile is a C=C double bond (usually an alkenic group and less frequently an aromatic group). Alkenic oxime mesylates enable intramolecular cyclization by an electrophihc addition of the double bond to the electrophilic intermediate. These reactions are terminated by a proton loss. 

However, polymerization through the alkene group is the dominant reaction. 1,4-Polymerization also occurs ... 

Cationic polymerization of acrolein has been reported to yield polymers containing both types of repeating units, although one would not expect the alkene group to be reactive toward cationic initiation. 

Similar facile cycloaddition-elimination reactions are observed when the nitrile group is replaced by an alkyne or alkene group. Thus, thermolysis of thiatriazolines (56) in refluxing benzene for 3 days provided the intramolecular adducts (57) (Equation (5)) <9314439 >. 

Two ciT-dihydroxylation reactions of alkenes formed steps in the synthesis of the antiviral drug (-)-oseltamvir ( tamiflu ) were carried out with RuO /aq. Na(IO )/ EtOAc-CH3CN/4°C [169]. Terminal alkene groups in nucleosides were oxidised to alcohols by RuClj/aq. Na(lO )/EtOAc-CH3CN/0°C thus 3,5-di-0-benzyl-l,2-di-O-isopropylidene-3-C-vinyl-a-D-ribofuranose (1) gave the diol (2) which, on cleavage with Na(lO ) and reduction with NaBH yielded 3,5-di-0-benzyl-l,2-di-O-isopropylidene-3-C-hydroxy-methyl-a-D-ribofuranose (3) (Fig. 3.4) [170]. 

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