Reaction decarbonylation

Pure cis-71 could be isolated in 65% yield and was characterized by means of x-ray structure analysis (Fe-Si 2.270(1)/2.272(1) A). This ds-conformer is exclusively formed. The formation of 71 requires a photoinduced silyl exchange followed by a decarbonylation reaction and further steps of an oxidative addition to the metal [176]. 

All these data could be obtained by means of two techniques, namely n.m.r. spectroscopy and the use of superacid solvent systems (such as HF—BF3, HF—SbFj, FHSO3—SbFs, SbFs—SOj). As will become evident in this article, this is equally true for the data of the carbonyl-ation and decarbonylation reactions (3). With less acidic systems the overall kinetics can, of course, be obtained but lack of knowledge concerning the concentrations of the intermediate ions prevents the determination of the rate constants of the individual steps. ... 

Secondly, the stabilization of alkylcarbonium ions can be conveniently determined by measuring the equilibrium constants of the carbonylation-decarbonylation reactions. For some cases the rates of carbonylation are used as a kinetic criterion for stabilization. 

The known CO insertion and decarbonylation reactions are surveyed in this section. Kinetic and stereochemical results already discussed in Sections II-IV have been given a cursory mention for the sake of completeness. Not comprehensively covered are processes which likely proceed via... 

Carbon monoxide insertion and decarbonylation reactions of rhodium complexes have been studied mainly in the context of investigations concerned with catalysis. 

Organomercurial carbonylation. Use of Co2(CO)g as a stoichiometric and as a catalytic reagent Organic synthesis reactions using palladium compounds Decarbonylation reactions using transition metal compounds... 

State decarbonylation reaction in total synthesis was reported recently in the case of natnral prodnct (+)-herbetenolide, which farther illustrates the exquisite control that the solid state may exert on the chemical behavior of the otherwise highly promiscuous reactive intermediates. As word or caution, it should be mentioned that intramolecular quenching effects known to act in solution can also affect that reaction in the solid state. Recently reported examples include the well-known intramolecular P-phenyl and electron transfer quenching. ... 

Hydrocarbon formation involves the removal of one carbon from an acyl-CoA to produce a one carbon shorter hydrocarbon. The mechanism behind this transformation is controversial. It has been suggested that it is either a decarbonylation or a decarboxylation reaction. The decarbonylation reaction involves reduction to an aldehyde intermediate and then decarbonylation to the hydrocarbon and releasing carbon monoxide without the requirement of oxygen or other cofactors [88,89]. In contrast, other work has shown that acyl-CoA is reduced to an aldehyde intermediate and then decarboxylated to the hydrocarbon, releasing carbon dioxide [90]. This reaction requires oxygen and NADPH and is apparently catalyzed by a cytochrome P450 [91]. Whether or not a decarbonylation reaction or a decarboxylation reaction produces hydrocarbons in insects awaits further research on the specific enzymes involved. 

Casey et al. have studied the decarbonylation reactions of [cis-(OC)4M(MeCO)(PhCO)], in which M is Mn or Re (16,17). These complexes lose a carbonyl ligand to form five-coordinate intermediates of the type [(OC)3M(MeCO)(PhCO)]. Reversible methyl migration proceeds much more rapidly than does phenyl migration. In the course of these studies, a phosphine substituted rhena-/3-diketonate complex, [fac-(OC)3(Et3P)Re(MeCO) (PhCO)], was prepared. 

The success of the phase space theory in fitting kinetic energy release distributions for exothermic reactions which involve no barrier for the reverse reaction have led to the use of this analysis as a tool for deriving invaluable thermochemical data from endothermic reactions. This is an important addition to the studies of endothermic reactions described above. As an example of these studies, consider the decarbonylation reaction 11 of Co+ with acetone which leads to the formation of the... 

Application of the decarbonylation reaction to cyclohepteno cyclopropenone (J9)43) led to the intermediate formation of the highly strained cycloheptyne (246) as indicated by the formation of its cyclotrimerization product 247 (in analogy to... 

Synthetic applications of other decarbonylation reactions are found in the conversion of cyclooctatetraene to barrelene 250), with the photodecarbonyla-tion of a Diels-Alder adduct as key step (2.31) and the preparation of tetrathioesters from 1,3-dithioles (2.32) 251). The most remarcable application of such a reaction up to date is the synthesis of tetra t.butyltetrahedrane from a tricyclic ketone precursor (2.33) 252). 

However, the decarbonylation reaction can be suppressed by the use of specially tailored chelating groups. Intermolecular processes involving dienes and salicylaldehydes are now known, and are thought to proceed via a double chelation mechanism, akin to the Jun-type system. Rhodium-catalyzed reactions lead to hydroacylated products, under relatively mild conditions (Equation (134)).117... 

In addition to cyclooctenone 143, the reaction of tethered alkene-vinylcyclobutanone 142 also produces cyclo-heptene 144 as a byproduct (Equation (22)). This product is thought to result from a decarbonylation reaction of a rhodacyclononenone intermediate. This result is discussed further in Section 10.13.3.3.129... 

The use of Pd/C to effect decarbonylation reactions, which has long been known, is equally successful with pyrrole aldehydes, e.g., 204 to 205 [108]. 

The facility of these decarbonylation reactions is obviously related to the donor capacity of the ligand groups. The halogens follow the variation that may be anticipated for this series. The reactions of Os COlnL with the halogen acids HX (X = Cl, Br, I) involve sequential evolution of carbon monoxide, but their facility increases with the donor capacity of the halogen, Cl < Br < I (157,162). 

Differential scanning calorimetry has been used88 to measure the enthalpy change, AH0 for the exothermic decarbonylation reaction... 

In the gas phase, this decarbonylation reaction is very efficient. Radical rearrangements, which are also possible if the change leads to a more stable product ... 

The thermolysis of certain members of the carbomethoxy series (146.C and 145.c) results in a decarbonylation reaction that affords the exclusively E -diene complexes 150 or the E/Z-diene complex mixtures 151, respectively. These products may be formed by direct thermolysis of the precursor cyclopropene (144) in the presence of diiron nonacarbonyl, isolated in 80% overall yield and in a approximate ratio of 3 2 1 (150 Z-151 -151), a product distribution matching that obtained from the isolated vinylketene... 

With phenyl phenylacetates, there is also PFR, but the decarbonylation reaction is an important process [281,282] product selectivity depends not only on the environment but also, in a very important manner, on the substituents of the ester molecule. 

Pure decarbonylation typically employs noble metal catalysts. Carbon supported palladium, in particular, is highly elfective for furan and CO formation.Typically, alkali carbonates are added as promoters for the palladium catalyst.The decarbonylation reaction can be carried out at reflux conditions in pure furfural (165 °C), which achieves continuous removal of CO and furan from the reactor. However, a continuous flow system at 159-162 °C gave the highest activity of 36 kg furan per gram of palladium with potassium carbonate added as promoter. In oxidative decarbonylation, gaseous furfural and steam is passed over a catalyst at high temperatures (300 00 °C). Typical catalysts are zinc-iron chromite or zinc-manganese chromite catalyst and furfural can be obtained in yields of... 

The plausible deoxygenation routes for production of diesel like hydrocarbons from fatty acids and their derivates are decarboxylation, decarbonylation, hydrogenation and decarbonylation/hydrogenation. The main focus in this study is put on liquid phase decarboxylation and decarbonylation reactions, as depicted in Figure 1. Decarboxylation is carried out via direct removal of the carboxyl group yielding carbon dioxide and a linear paraffinic hydrocarbon, while the decarbonylation reaction yields carbon monoxide, water and a linear olefinic hydrocarbon. 

From the very good activity of thermally or electrochemically activated CoTAA for the reaction of CO one might deduce that the oxidation of formic or oxalic acid proceeds, not directly, but by way of a preliminary decarbonylization reaction. However, there is no evolution of gas from CoTAA in a solution of formic acid in dilute sulfuric acid, even at 70 °C. Such a reaction would have to occur on chemical decomposition of formic acid, with evolution of CO and H2O, or CO2 and H2. It may thus be assumed that formic acid is oxidized directly. 

Further examples of decarbonylation reactions are given below.12,13... 

On the other hand, in bi- or polycyclic molecules a decarbonylation reaction such as a [5 -> 4 + 1] fragmentation of a five-membered ring is quite common. However, in these cases the reaction is not accompanied by ring contraction. As an example, norbornen-7-one (16) affords cyclohexadiene (86CP307 90JA5089). 

Perhaps the most industrially feasible approach has been developed by Rich and co-workers at General Electric, a palladium-catalyzed silylative decarbonylation reaction of aromatic acid chlorides with disilanes [Eq. (35)].97 One of the silicon centers from the disilane is transferred to the arene whereas the other acts as a chloride acceptor to produce the chlorosi-... 

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