Olefins aldehyde formation

In 1998, Wakatsuki et al. reported the first anti-Markonikov hydration of 1-alkynes to aldehydes by an Ru(II)/phosphine catalyst. Heating 1-alkynes in the presence of a catalytic amount of [RuCljlCgHs) (phosphine)] phosphine = PPh2(QF5) or P(3-C6H4S03Na)3 in 2-propanol at 60-100°C leads to predominantly anti-Markovnikov addition of water and yields aldehydes with only a small amount of methyl ketones (Eq. 6.47) [95]. They proposed the attack of water on an intermediate ruthenium vinylidene complex. The C-C bond cleavage or decarbonylation is expected to occur as a side reaction together with the main reaction leading to aldehyde formation. Indeed, olefins with one carbon atom less were always detected in the reaction mixtures (Scheme 6-21). 

The most useful methods for the formation of C-C bonds are based on the addition of C-nucleophiles to carbonyl compounds. Among the many variations of this basic scheme phosphorus ylides, capable of olefinating aldehydes or ketones in a single step, have proven to be exceedingly valuable reagents in organic synthesis. 

Although Eq. (3) indicates that CO absorption is required for aldehyde formation, it has been shown by Karapinka and Orchin 18) that at 25° and with a moderate excess of olefin the rate of reaction and the yield of aldehyde are similar when either 1 atm of CO or 1 atm of Nj is present. Obviously CO is not essential for the reaction and a CO-deficient intermediate, probably an acylcobalt tricarbonyl, can be formed under these conditions. The relative rates of HCo(CO)4 cleavage of tricarbonyl and tetracarbonyl are not known, and thus the stage at which CO is absorbed in the stoichiometric hydroformylation of olefins under CO is not known with certainty. Heck (19) has shown conclusively that acylcobalt tetracarbonyls are in equilibrium with the acylcobalt tricarbonyl ... 

In many manufacturing processes there exists the potential for aldehyde formation. Often these aldehydes occur in low concentrations in the presence of much higher levels of aliphatics, olefinics and aromatic hydrocarbons. Gas chromatography or combined gc/ms methods are often ineffective in determining aldehydes in such a matrix. Several wet chemical techniques have been devised for estimating the total aldehyde concentration in these streams, but quantitation of the individual aldehydes has remained a difficult task. 

The same group has also reported the use of dithiane functionalized olefinic aldehydes in an intramolecular process. Treatment of 289 with the secondary amine 290 led to the formation of the intermediate ylide 291, which delivered a range of tricyclic products (292) in high material yield as essentially a single stereoisomer after in situ cycloaddition (Scheme 3.95). 

The potential of benzoylformate decarboxylase (BFD, E.C. 4.1.1.7) to catalyze C-C bond formation was first reported by Wilcocks at al. using crude extracts of Pseudomonas putidsL [50]. They observed the formation of (S)-2-hydroxy-l-phenylpro-panone (S)-2-HPP when benzoyl formate was decarboxylated in the presence of acetaldehyde. Advantageously, aldehydes - without a previous decarboxylation step - can be used instead of the corresponding more expensive a-keto acids [51]. We could show that BFD is able to bind a broad range of different aromatic, heteroaromatic, and even cyclic aliphatic and conjugated olefinic aldehydes to ThDP before ligation to acetaldehyde or other aldehydes (Table 2.2.7.3) [52]. 

Two-oxygen addition to the olefin with formation of aldehydes, as an effect of the addition of oxygen to the C-C double bond with cleavage of the double bond of the olefin, and the relevant acids (Scheme 7.10, lower part). 

Aldehyde Formation. Several investigators observed a marked dominance of hexanal in the volatile products of low-temperature oxidation. At the higher temperatures, however, 2,4-decadienal was the major aldehyde formed (19,20,21). Both aldehydes are typical scission products of linoleate hydroperoxides. Swoboda and Lea (20) explained this difference on the basis of a selective further oxidation of the dienal at the higher temperature, while Kimoto and Gaddis (19) speculated that the carbon-carbon bond between the carbonyl group and the double bond (Type B) is the most vulnerable to cleavage under moderate conditions of autoxidation, while scission at the carbon-carbon bond away from the olefinic linkage (Type A) is favored under stress such as heat or alkali. 

In the metallic palladium-catalyzed carbonylation of olefins, some hydrogen sources are essential hydrogen halide and molecular hydrogen were found to be the most eflFective. The following sequence of reactions was proposed for the reaction mechanism of the ester and aldehyde formation catalyzed by palladium (23). The first step of the metallic palladium-catalyzed carbonylation seems to be the formation of a palladium-hydrogen bond by the oxidative addition of hydrogen chloride... 

It is known that insertion of carbon monoxide to form an acyl complex is reversible, in which results depend on the pressure of carbon monoxide and temperature. If the above-mentioned mechanisms are correct, then acyl halides and aldehydes should be decarbonylated to form olefins provided that an acyl-palladium bond is formed by the oxidative addition of acyl halides or aldehydes to metallic palladium. This proved to be the case. When acyl halide was heated with a catalytic amount of metallic palladium or palladium chloride at 200°C. in a distilling flask, carbon monoxide and hydrogen halide were evolved rapidly, and olefin was collected in a good yield. This reaction is a new and useful preparative method of olefins. In the same way, aldehydes can be decarbonylated smoothly, but in this case, both olefin and the corresponding paraffin Were obtained. The latter probably arises by the hydrogenation of the olefin. Decarbonylation of certain aldehydes has been reported by several workers (3, 6), but no reasonable mechanism has been known. The mechanism of the palladium-catalyzed aldehyde formation discussed above gives clear explanation for the palladium catalyzed decarbonylation of aldehydes. 

The ozonolysis was therefore repeated under a variety of conditions and new curves were constructed for each. The results were best at low temperature (—78° C. was better than —53° C.), at a high olefin concentration (as high as the solubility limitations would permit), in nonpolar solvents, and with a small amount of pyridine present in the solvent. The dramatic effect of the inclusion of approximately 1% pyridine is shown in Figure 3. The selectivity was greatly improved, the nuclear double bond remaining intact until the side-cham double bond had almost completely reacted. The aldehyde formation curve indicates that approximately two molecules of aldehyde were formed from the cleavage of each double bond. These curves represent optimal conditions and were selected from runs at various pyridine concentrations. 

The possible sources of isomeric aldehyde formation include olefin isomerization, regioselectivity of the addition of the hydridocobalt carbonyl to the olefin, isomerization of the alkylcobalt carbonyl, and isomerization of the acylco-balt carbonyl species. There is no evidence for an isomerization of the alkylcobalt carbonyl species under the conditions of industrial oxo synthesis (high pressure) [96]. In contrast, the isomerization of a coordinated olefin is well known and a plethora of studies have proven this behavior [4]. 

For higher olefins such as 1-hexene, solvents are necessary to perform the hydroformylation reaction. The overall rate measured for aldehyde formation is strongly dependent on the polarity of these solvents. Alcohols like methanol and ethanol increase the rate up to tenfold compared with nonpolar solvents such as n-hexane or toluene [107]. It was suggested that cationic and anionic catalyst species such as [Co(S)(CO)3] and [HCo6(CO)ts] are responsible for this effect (S = solvent). However, this proposal is based on kinetic data only and no spectroscopic evidence has been given. 

Some exceptions to the general rules occur. Cyclopentene is completely combusted, undoubtedly because of the high reactivity of cyclo-pentadiene. 4,4-Dimethyl-1-pentene is expected to produce an unsaturated aldehyde, but instead 2,3-dimethylpentadiene is the initial product. A methyl shift from a quarternary carbon is apparently easy, permitting formation of a diene instead of the oxygenated compound. 3,3-Dimethyl-l-butene is not expected to react at all under the general rules, but here also a methyl shift occurs so that diene, olefin aldehyde, diene aldehyde, and diene dialdehyde are formed. The reactivity of the latter olefin relative to 1-butene, measured by oxidation of a mixture at low conversion, was 0.21, while that of 4,4-dimethyl-1-pentene was 0.75. These reactivities suggest that isomerization occurs before reaction for 3,3-dimethyl-l-butene, while isomerization probably occurs after the aUyl intermediate is formed in the case of the pentene. 

Grubbs and coworkers (35) while examining Rh and Co catalysts derived from 14 reported the loss of infrared CO stretches and visual darkening of the catalysts after use for hydrogenation of olefins, aldehydes or ketones, cyclohexene disproportionation to benzene and cyclohexane or the cyclotrimerization of a wide variety of acetylenes. Stille (36) using a rhodium catalyst prepared from 14 observed activity for the hydrogenation of benzene that increased with reuse, a phenomenon usually associated with metal crystallite formation. Rhodium catalysts of 15 and 16 used to hydroformylate octene-1 revealed a loss of carbonyl adsorptions and a loss in catalytic activity upon reuse (37). 

From singlet state it has been found that the following reactions often compete with the 1,3-rearrangements cis-trans isomerization, decarbonyl ation, aldehyde formation, ketene formation, olefin reduction, Norrish t q)e-II cleavage with cydobutanol formation, [2-J-2] cycloaddition, and inter tem crossing with concomitant 1,2-acyl shift. From the triplet state a similar series of reactions have been reported including 1,3-acyl shift. 

Evidence for this mechanism is as follows 1) there is a first order dependence of the initial rate of aldehyde formation on the t-butanol concentration in DMF solvent 2) the use of n-butanol or s-butanol leads to ketal and acetal products, although those derived from s-butanol readily decompose to the ketone and aldehyde under the reaction conditions 3) the selectivity for aldehyde increases as n-butanol < s-butanol < t-butanol 4) small amounts of water increase the rate, but larger amounts decrease aldehyde selectivity probably due to competing attack by water on the coordinated olefin and 5) non-protic solvents such as THE give much lower rates and aldehyde selectivities. 

A similar type of chiral rhodium porphyrin was found to be effective for the carbene-insertion reaction to olefins, where formation of the carbene complex takes place. Chiral rhodium complexes for catalytic stereoselective-carbene addition to olefins were prepared by condensation of a chiral aldehyde and pyrrole. Formation of the metal-carbene complex and substrate access to the catalytic center are crucial to the production of optically active cyclopropane derivatives. Optically active a-methoxy-a-(trifluoro-methyOphenylacetyl groups are linked witfi the amino groups of a,p,0L,p isomers of tetrakis-(2-aminophenyI)por-phyrin through amide bonds. Oxidation reactions of the... 

Chromyl chloride, a volatile liquid with a formal Cr oxidation state of VI, has been found to add oxygen to terminal olefins with formation of aldehydes ... 

BED [EC 4.1.1.7] is derived from mandelate catabolism, where it catalyzes the nonoxidative decarboxylation of benzoyl formate to yield benzaldehyde. Again, the reverse carboUgatiMi reaction is more important [1488-1490]. As may be deduced from its natural substrate, is exhibits a strong preference for large aldehydes as donor substrates encompassing a broad range of aromatic, heteroaromatic, cyclic aliphatic and olefinic aldehydes [1480]. With acetaldehyde as acceptor, it yields the complementary regio-isomeric product to PDC (Scheme 2.200). 

The formation of a dithioacetal as an intermediate in organic synthesis is not new to most chemists. However, in recent years there has been a continuing improvement in the methods of preparation as well as the subsequent reactions. The early use of the dithioacetal group as a means to reduce carbonyl functions with Raney nickel has been expanded to extensive use as a protecting group, methylene blocking group and as an intermediate in the preparation of complex hydrocarbons, olefins, aldehydes and ketones. 

According to the given equation, the formation of diethylketone is favored by an excess of the olefin because the concentration of hydridocarbonyl needed for aldehyde formation is very small. At higher ratios of C2H4/H2, it is possible to obtain a reaction mixture containing 85 % of the ketone. As the chain length of the alkene increases, the yield of the ketone rapidly decreases. 

Isomerization of the Olefin. The formation of isomeric olefins by double bond shifts and as a consequence the formation of aldehydes other than those expected on the basis of attachment of the formyl group to one of the two carbon atoms of the original double-bond is most pronounced with cobalt catalysts. Unmodified rhodium catalyst is also effective in olefin isomerization. 

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