Alkene derivatives catalytic reactions

Among several propargylic derivatives, the propargylic carbonates 3 were found to be the most reactive and they have been used most extensively because of their high reactivity[2,2a]. The allenylpalladium methoxide 4, formed as an intermediate in catalytic reactions of the methyl propargylic carbonate 3, undergoes two types of transformations. One is substitution of cr-bonded Pd. which proceeds by either insertion or transmetallation. The insertion of an alkene, for example, into the Pd—C cr-bond and elimination of/i-hydrogen affords the allenyl compound 5 (1.2,4-triene). Alkene and CO insertions are typical. The substitution of Pd methoxide with hard carbon nucleophiles or terminal alkynes in the presence of Cul takes place via transmetallation to yield the allenyl compound 6. By these reactions, various allenyl derivatives can be prepared. 

Enynes 71 react with aldehydes 61 in the presence of the [Ni(COD)J/SIPr catalytic system to afford two distinct products 72 and 73 (Scheme 5.20) [20b], The enone 72 is derived from aldehyde addition with the alkyne moiety while the adduct 73 arises from the aldehyde addition with the alkene moiety. The product distribution is dependent on the substituent on either the alkyne or alkene moieties. The reaction between 71 and ketones 74 led to the unprecedented formation of pyrans 75 (Scheme 5.20). The reaction showed to be highly regioselective in aU the cases, the carbonyl carbon was bound to the olefin. 

The data in Table 11 show some facts, the mechanistic consequences of which will be discussed in Sect 2.4.4. The 2-alkene/l-alkene ratio for the catalytic reaction differs significantly from that for the homogeneous decomposition. On all catalysts, this ratio is higher for the 2-bromo-than for the 2-chloro-derivative therefore the orientation also depends on the nature of the halogen. On some catalysts, both ratios (the 2-/1- and cis/ trans) are equal or approximately the same as the equilibrium values, but on other catalysts, significant differences appear. 

It was discovered by Roelen in 1938 and is the oldest and largest volume catalytic reaction of alkenes, with the conversion of propylene to butyraldehyde being the mosi important. About 5 million tons of aldehydes and aldehyde derivatives (mostly alcohols) are produced annually making the process the most important industrial synthesis using a metal carbonyl complex as a catalyst. The name hydroformylation arises from the fact that in a formal sense a hydrogen atom and. formyl group are added across a double bond. The net result of the process is extension of (he carbon chain by one and introduction of oxygen into the molecule. 

Doubly acceptor-activated imines with an intramolecular alkene moiety such as 29 can cyclize according to an electrophilic mechanism to give pyrrolidine, piperidine or azepine derivatives. This reaction is induced by stoichiometric amounts of Lewis acids, preferably trialkylsilyl triflates [38]. In certain cases FeCl3 can also be used, for example for the preparation of azepinolactone 30 from imine 29 (Scheme 8.10) [39]. Catalytic amounts of FeCl3 are required for the addition of diethyl phosphite to an... 

Catalytic Processes. Catalytic processes lead to intramolecular and intermolecular C-C bond constructions which are usually directly analogous to the stoichiometric reactions. This topic was reviewed in 1983. Catalytic processes often lead to reduction rather than alkene regeneration this is more likely to happen with B12 as a catalyst than it is with a cohaloxime. Schef-fold pioneered the use of vitamin B12 as a catalyst for C-C bond formation, and Tada pioneered the use of model complexes such as cobaloximes. Several of the reactions described in the section on stoichiometric reactions have also been performed cat-aly tically, as mentioned in that section. Commonly used chemical reductants include Sodium Bomhydride and Zinc metal. Electrochemical reduction has also been used. A novel catalytic system with a Ru trisbipyridine unit covalently tethered to a B12 derivative has been used for photochemically driven catalytic reactions using triethanolamine as the reductant. A catalytic system using DODOH complexes can lead to reduction products or alkene regeneration depending upon the reaction conditions. These catalytic B12 and model complex systems all utilize a... 

The selective production of methanol and of ethanol by carbon monoxide hydrogenation involving pyrolysed rhodium carbonyl clusters supported on basic or amphoteric oxides, respectively, has been discussed. The nature of the support clearly plays the major role in influencing the ratio of oxygenated products to hydrocarbon products, whereas the nuclearity and charge of the starting rhodium cluster compound are of minor importance. Ichikawa has now extended this work to a study of (CO 4- Hj) reactions in the presence of alkenes and to reactions over catalysts derived from platinum and iridium clusters. Rhodium, bimetallic Rh-Co, and cobalt carbonyl clusters supported on zinc oxide and other basic oxides are active catalysts for the hydro-formylation of ethene and propene at one atm and 90-180°C. Various rhodium carbonyl cluster precursors have been used catalytic activities at about 160vary in the order Rh4(CO)i2 > Rh6(CO)ig > [Rh7(CO)i6] >... 

Thus, a new type of Lewis acid, lanthanide triflates, is quite effective for the catalytic activation of imines, and has achieved imino Diels-Alder reactions of imines with dienes or alkenes. The unique reactivities of imines which work as both dienophiles and azadienes under certain conditions were also revealed. Three-component coupling reactions between aldehydes, amines, and dienes or alkenes were successfully carried out by using Ln(OTf)3 as catalysts to afford pyridine and quinoline derivatives in high yields. The triflates were stable and kept their activity even in the presence of water and amines. According to these reactions, many substituted pyridines and quinolines can be prepared directly from aldehydes, amines, and dienes or alkenes. A stepwise reaction mechanism in these reactions was suggested from the experimental results. 

A variety of arenes and heteroarenes react with alkenes in the presence of palladium(II) derivatives to produce alkenyl substitution products. Three methods are commonly employed for the in situ preparation of palladium derivatives (i) direct metallation of an arene or heteroarene with a Pd(II) salt (ii) exchange of the organic group from a main-group organometallic to a Pd(II) compound (iii) oxidative addition of an organic halide, an acetate, or triflate salt to Pd(0) or a Pd(0) complex. For catalytic reactions Cu(II) chloride or p-benzoquinone is usually used to reoxidize Pd(0) to Pd(II). 

It was found that if the content of the hydrocarbons extracted by supercritical 2-methyl-butane were analyzed, no hydrocarbons other than C12 alkene (two isomers) were detected. It is clear that C12 alkene, derived from oligomerization reactions, deposited onto catalytic sites and deactivated the catalyst. More specifically, high molecular weight alkenes such as C12, which have high electron density, might combine strongly with Lewis acid sites inside... 

---