Alkenes pioneering studies

Fischer-Tropsch Process. The Hterature on the hydrogenation of carbon monoxide dates back to 1902 when the synthesis of methane from synthesis gas over a nickel catalyst was reported (17). In 1923, F. Fischer and H. Tropsch reported the formation of a mixture of organic compounds they called synthol by reaction of synthesis gas over alkalized iron turnings at 10—15 MPa (99—150 atm) and 400—450°C (18). This mixture contained mostly oxygenated compounds, but also contained a small amount of alkanes and alkenes. Further study of the reaction at 0.7 MPa (6.9 atm) revealed that low pressure favored olefinic and paraffinic hydrocarbons and minimized oxygenates, but at this pressure the reaction rate was very low. Because of their pioneering work on catalytic hydrocarbon synthesis, this class of reactions became known as the Fischer-Tropsch (FT) synthesis. 

The thermal decompositions are catalyzed by Bronsted and Lewis acids [68]. In general, when M is electron poor and Lewis acidic, the thermal decompositions occur efficiently and at low temperatures (typically between 100 and 200 °C, but sometimes at lower temperature). The addition of a catalytic amount of a Lewis or Bronsted acid (i.e., AICI3 or HCl) has been observed to accelerate the ehmination of isobutylene and the formation of three-dimensional network structures [64,124-126]. Pioneering studies on pyrolyses of various metal alkoxides by Bradley and others have also shown that alkene eliminations represent a primary decomposition pathway [104]. 

Hydrozirconation of terminal alkynes R-C=CH (R= aryl, alkyl) with 1 affords terminally ( )-Zr-substituted alkenes with high efficiency and excellent stereochemical and regiochemical control (>98%). These alkenylzirconocene complexes are of particular interest for synthetic use [136, 143, 144]. Moreover, beside the electropositive halogen sources [145] and heteroatom electrophiles [3] used in the pioneering studies to directly cleave the Zr-C bond, ( )-vinyl-Zr complexes were recently transformed into a number of other trans-functionalized alkenes such as ( )-vinyl-sul-fides[146], vinylic selenol esters [147], vinyl-sulfones [148], vinyl-iodonium [149], vinyl-(R0)2P(0) [150], and vinilic tellurides [143]. 

Cyclopropanation reactions can be promoted using copper or rhodium catalysts or indeed systems based on other metals. As early as 1965 Nozaki showed that chiral copper complexes could promote asymmetric addition of a carbenoid species (derived from a diazoester) to an alkene. This pioneering study was embroidered by Aratani and co-workers who showed a highly enantioselective process could be obtained by modifying the chiral copper... 

The addition of a single-bonded reagent across a multiple bond is one of the fundamental reactions of organic radicals. The basic principles of this reaction were first advanced by Kharasch in pioneering studies on the mechanism of the peroxide-initiated anti-Maikovnikov addition of hydrogen bromide to alkenes.1 In the atom transfer method, the generation and removal of radicals are coupled and occur in the key atom transfer step. Compared to other methods, the atom transfer method provides unique options for synthetic reactions. But there are also important limitations. Recently, there has been a renewed interest in the application of the characteristics of atom transfer reactions in synthesis and new developments have been reviewed.5,161... 

Intermolecular meta cycloadditions provide yet another option for the facile [SC -i- 2C] construction of seven-membered rings, as illustrated in Srinivasan s pioneering studies (Scheme 24). The availability of simple arenes and alkenes and of numerous methods as discussed above for the modification of meta cycloadducts makes this a particularly effective stategy for cycloheptanoid synthesis. 

The pioneering studies in this area were reported in 1999 by Narasaka, who demonstrated intramolecular heteroatom Heck-type reactions of 0-pentafluorobenzoyl oximes [97]. As shown below, treatment of unsaturated substrate 97 with a catalytic amount of Pd(PPh,y in the presence of triethyl amine provided pyrrole 98 upon workup with chlorotrimethylsilane. The mechanism of this reaction proceeds via oxidative addition of the N—O bond to afford 99, which undergoes alkene insertion into the Pd—N bond to provide alkyl-palladium complex 100. The exo-methylene product 101 is generated by [i-hydride elimination from 100, and isomerization to the desired pyrrole 98 occurs when chlorotrimethylsilane is added. 

Pioneering studies on C—C-bond formations through C—H bond cleavages employed phenols [41] or aromatic ketones [42] for arylations of alkenes through chelation assistance (Scheme 9.9). 

These pioneering studies by Heck have opened the way to a new reaction later called the Mizoroki-Heck reaction (Scheme 1.1). In 1971, Mizoroki et al. reported preliminary results on the PdCh-catalysed arylation of alkenes by iodobenzene in the presence of potassium acetate as base (Scheme 1.5) [4]. No new contribution to the mechanism was proposed, except that palladium particles, formed in situ in the reaction or deliberately added, were suggested to be the active catalyst [4]. 

The dimerization of alkenes is an important method for the production of higher olefins as well as oligomers that find extensive application as industrial intermediates. The stimulus in this direction was provided by the pioneering studies of Ziegler in the early 1950s. He explored the use of organoaluminum compounds in the selective dimerization of alkenes [1,2]. 

Pioneering studies by Emmet suggested in 1953 that ethylene acts as a chain initiator in Fe-catalyzed Fischer-Tropsch reactions. Many authors have used isotopi-cally labeled olefins to confirm that 1-alkenes are the primary reaction products (although they are thermodynamically instable under the reaction conditions). For instance, Somorjai s group has shown, using a polycrystalline iron sheet (1 cm ), that the addition of ethylene or propene in the syn gas increases the length of the polymer chain. These olefins readsorb and readily form polymers by insertion into adsorbed C fragments. Thus, the Fischer-Tropsch mechanism involves two steps, namelly the formation of olefins and their polymerization ... 

The applications of palladium-catalyzed allylation reactions in the realm of total synthesis have been numerous, owing to the general functional group tolerance and high stereoselectivity observed in these transformations [8,17, 25, 27, 30]. In pioneering studies, Trost reported that alkene 1 was converted into allylpalladium complex 2 on treatment with a stoichiometric amounts of palladium dichloride (Scheme 14.1) [42]. Nucleophilic substitu-... 

Acylzirconocene chloride derivatives are readily accessible in a one-pot procedure through the hydrozirconation of alkene or alkyne derivatives with zirconocene chloride hydride and subsequent insertion of carbon monoxide into the alkyl- or alkenyl-zirconocene bond under atmospheric pressure. The pioneering study on the preparation and reactivity of acylzirconocene dated back to the initial study of Schwartz [27] and revealed that an acyl group can be converted into a large variety of carboxylic acid derivatives (Scheme 12.22). 

Notwithstanding the drawbacks to the method, the addition of nitrenes to alkenes is a well studied classical method for direct aziridination. The original reactions (often involving alkoxycarbonylnitrenes) employed harsh conditions, resulting in nonstereoselective transformations. In these pioneering reports, the requi-... 

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