Isoprene reactions with carbonyl compounds

The interest in chiral titanium(IV) complexes as catalysts for reactions of carbonyl compounds has, e.g., been the application of BINOL-titanium(IV) complexes for ene reactions [8, 19]. In the field of catalytic enantioselective cycloaddition reactions, methyl glyoxylate 4b reacts with isoprene 5b catalyzed by BINOL-TiX2 20 to give the cycloaddition product 6c and the ene product 7b in 1 4 ratio enantio-selectivity is excellent - 97% ee for the cycloaddition product (Scheme 4.19) [28]. 

A study of the reactions of butadiene, isoprene, or allene coordinated to nickel in a metallacycle, with carbonylic compounds, has been reported by Baker (example 11, Table IV). In the presence of phosphines, these metallacycles adopt a cr-allyl structure on one end and a ir-allyl structure on the other, as mentioned in Section II,A,1. The former is mainly attacked by aldehydes or electrophilic reagents in general, the latter by nucleophiles (C—H acids, see Table I, or amines, see Table IX). 

Such copolymers of oxygen have been prepared from styrene, a-methylstyrene, indene, ketenes, butadiene, isoprene, l,l-diphen5iethylene, methyl methacrjiate, methyl acrylate, acrylonitrile, and vinyl chloride (44,66,109). 1,3-Dienes, such as butadiene, yield randomly distributed 1,2- and 1,4-copolymers. Oxygen pressure and olefin stmcture are important factors in these reactions for example, other products, eg, carbonyl compounds, epoxides, etc, can form at low oxygen pressures. Polymers possessing dialkyl peroxide moieties in the polymer backbone have also been prepared by base-catalyzed condensations of di(hydroxy-/ f2 -alkyl) peroxides with dibasic acid chlorides or bis(chloroformates) (110). 

Et2Zn also participates in the reductive coupling as a formal hydride source. Results for the Ni-catalyzed, Et2Zn-promoted homoallylation of carbonyl compounds with isoprene are summarized in Table 7 [30]. Et2Zn is so reactive that for the reaction with reactive aromatic aldehydes it causes direct ethylation of aldehydes, and the yields of homoallylation are diminished (runs 1 and 2). Unsaturated aldehydes seem to be subject to the Michael addition of Et2Zn. Accordingly, for the reaction with cinnamaldehyde, none of the expected homoallylation product is produced instead, the 1,4-addition product of Et2Zn, 3-phenylpentanal is produced exclusively (run 3). 

Complexes 17-19 can be written in one valence structure as a, /3-unsaturated carbonyl compounds in which the carbonyl oxygen atom is coordinated to a BF2(OR) Lewis acid. The C=C double bonds of such organic systems are activated toward certain reactions, like Diels-Alder additions, and complexes 17-19 show similar chemistry. Complexes 17 and 18 undergo Diels-Alder additions with isoprene, 2,3-dimethyl-1,3-butadiene, tram-2-methyl-l,3-pentadiene, and cyclopentadiene to give Diels-Alder products 20-23 as shown in Scheme 1 for complex 17 (32). Compounds 20-23 are prepared in crude product yields of 75-98% and are isolated as analytically pure solids in yields of 16-66%. The X-ray structure of the isoprene product 20 has been determined and the ORTEP diagram (shown in Fig. 3) reveals the regiochemistry of the Diels-Alder addition. The C-14=C-15 double bond distance is 1.327(4) A, and the... 

As Barr et al. (2003) pointed out, the importance of such emissions is determined mainly by their impact on the three processes taking place in the atmosphere. The first consists in that such NMHCs as isoprene form in the course of carboxylization in plants and contribute much thereby to the formation of biospheric carbon cycle. The second process is connected with NMHCs exhibiting high chemical activity with respect to such main oxidants as hydroxyl radicals (OH), ozone (03), and nitrate radicals (N03). Reactions with the participation of such components result in the formation of radicals of alkylperoxides (R02), which favor efficient transformation of nitrogen monoxide (NO) into nitrogen dioxide (N02), which favors an increase of ozone concentration in the ABL. Finally, NMHC oxidation leads to the formation of such carbonyl compounds as formaldehyde (HCHO), which stimulates the processes of 03 formation. Finally, the oxidation of monoterpenes and sesquiterpenes results in the intensive formation of fine carbon aerosol with a particle diameter of <0.4 pm... 

Gas-phase ozonolyses of ethene, cis- and trans-but-2-ene, isoprene, as well as several monoterpenes such as o-pinene, /3-pinene, 3-carene, limonene, and /3-myrcene have been performed by trapping the reaction products in C>2-doped argon matrices and recording the IR spectra <2000SAA2605>. Bands characteristic for the secondary ozonides were identified after bleaching by broad-band UV-Vis photolysis. In the case of isoprene 34, a secondary ozonide appears to be formed more likely at the more substituted double bond however, the two possible carbonyl compounds 35 and 36 could not be put into evidence by infrared (IR) in the reaction condensate as these reacted further with O3 (Scheme 6). 

In the presence of strong acids such as aqueous H2SO4, carbonyl compounds may react with olefins to form unsaturated alcohols and other products, depending on the reaction conditions. Using H-mordenite as catalyst in a continuous-flow system, 10% conversion of formaldehyde to isoprene was observed at 300° using an isobutylene-to-HCHO (molar) ratio of 3.7. A carbonium ion-type reaction scheme, involving a Prins reaction (1,2) and a subsequent dehydration-rearrangement step... 

Although presently lacking industrial importance, alternating copolymers can be made from propylene and butadiene, also from propylene and isoprene. Copolymers of propylene and butadiene form with vanadium- or titanium-based catalysts combined with aluminum. alkyls. The catalysts have to be prepared at very low temperature (-70 C). Also, it was found that a presence of halogen atoms in the catalyst is essential.Carbonyl compounds, such as ketones, esters, and others, are very effective additives. A reaction mechanism based on alternating coordination of propylene and butadiene with the transition metal was proposed by Furukawa. ... 

Isoprene and the terpenes may be attacked by OH, NO3 and O3. The rate coefficients at room temperature for reaction with isoprene are of the order of 10 , 10 and 10 cm molecule" s , respectively. In the case of attack by OH, and in the presence of oxygen, a peroxy-hydroxy radical is formed up to six isomers may be produced. Product studies indicate that the initial addition is to one of the terminal carbon atoms. The peroxy-hydroxy radical may then either react with NO or with other RO2 radicals (including HO2) to form a variety of products, as indicated in Fig. 11. Under conditions where the peroxy-hydroxy radical reacts exclusively with NO, approximately 50 % of the carbon balance is accounted for by three main products methacrolein, methyl vinyl ketone and formaldehyde. Other carbonyl products and hydroxy-nitrates are thought to make up the carbon balance although there is presently no clear indication of the exact identity of these compounds or their yields. 

Percent product distribution Methylvinylketone (MVK) 49.0 1.1, metha-croleine (MAC) 44.3 1.6, 3-methyl-fiiran (MFU) 6.7 0.6 for isoprene mole fractions 400 ppm. The ratio of MVK to MAC under these conditions was 1.1 0.6. In the presence of NO the ratio is close to 1.4 [4]. Computer simulations based on our results for methylsubstituted 1-butenes showed that the observed [MVK]/[MAC] ratios are obtained with essentially equal probabilities for OH attack at the two double bonds of isoprene. This result contradicts predictions based on OH reaction rate coefficients for various methylsubstituted butenes [5]. Similar to results obtained for the 1-butenes, diols and hydroxy carbonyl compounds were found in small yields among the products. These are not included in the above product distribution because they are difficult to quantify. ... 

The use of the cobalt triad carbonyls as catalysts continues to provide many papers for this report. Publications cover the silylformylation of 1-Hexyne catalyzed by diodium-cobalt carbonyl clusters the formation of hydroxycarbene cobalt carbonyl derivatives, the use of rhodium cluster carbonyls in the water-gas shift reaction Rh4(CO) 2> and Co3Rh(CO)] 2 catalysts for the hydrosilation of isoprene, cyclohexanone and cyclohexenone catalytic reduction of NO by CO and the carbonylation of unsaturated compounds The chemistry of iridium carbonyl cluster complexes has been extended by making use of capping reactions with HgCl2and Au(PPh3)Q... 

Another addition to polymers with main-chain unsaturation is the Prins reaction between ethylenic hydrocarbons and compounds containing aldehy-dic carbonyl groups. Kirchof, in 1923, described the reaction of natural rubber in benzene solution with aqueous formaldehyde in the presence of concentrated sulfuric acid. The general reaction of an aldehyde, RCHO, with a poly-isoprene in the presence of an inorganic or organic acid or an anhydrous metal salt is represented by... 

Monomers with electron-rich double bonds produce one-to-one copolymers with monomers having electron-poor double bonds in reaction systems that also contain certain Lewis acids. These latter are halides or alkyl halides of nontransition metal elements, including AlCb, ZnCh, SnCL, BF3, AI(CH2CH3)Cl2, alkyl boron halides, and other compounds. The acceptor monomer generally has a cyano or carbonyl group conjugated to a vinyl double bond. Examples are acrylic and methacrylic acids and their esters, acrylonitrile, vinyl ketones, maleic anydride, fumaric esters, vinylidene cyanide, sulfur dioxide, and carbon monoxide. The variety of donor molecules is large and includes various olefins, styrene, isoprene, vinyl halides and esters, vinylidene halides, and allyl monomers [30]. 

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