Aldehydes unsaturated, oxidation

Physical and Chemical Properties. The (F)- and (Z)-isomers of cinnamaldehyde are both known. (F)-Cinnamaldehyde [14371-10-9] is generally produced commercially and its properties are given in Table 2. Cinnamaldehyde undergoes reactions that are typical of an a,P-unsaturated aromatic aldehyde. Slow oxidation to cinnamic acid is observed upon exposure to air. This process can be accelerated in the presence of transition-metal catalysts such as cobalt acetate (28). Under more vigorous conditions with either nitric or chromic acid, cleavage at the double bond occurs to afford benzoic acid. Epoxidation of cinnamaldehyde via a conjugate addition mechanism is observed upon treatment with a salt of /-butyl hydroperoxide (29). 

The unsaturated 3a-acetoxy-17-formyl-16-etiocholen-lip-ol-18-one lip,18-lactol is hydrogenated in the presence of palladium catalyst to saturate the 16,17-double bond, and then saturated aldehyde are oxidized by treatment with chromic oxide in pyridine to give 3a-acetoxy-lip-ol-18-one-pregnane lip,18-lactone 17-carboxylic acid. 

The volatiles from cooked meat contain large numbers of aliphatic compounds including aldehydes, alcohols, ketones, hydrocarbons and acids. These are derived from lipids by thermal degradation and oxidation (J7) and many may contribute to desirable flavor. In addition, the aldehydes, unsaturated alcohols and ketones produced in these reactions, as well as the parent unsaturated fatty acids, are reactive species and under cooking conditions could be expected to interact with intermediates of the Maillard reaction to produce other flavor compounds. 

Conjugated—a,/)-unsaturated or aromatic—aldehydes are oxidized by manganese dioxide in the presence of one equivalent of sodium cyanide to give an acyl cyanide (Formula C in Figure 17.18) via an intermediate cyanohydrin (B in Figure 17.18), which is also either an allylic or a benzylic alcohol. Alcohols of this kind can be oxidized by a relatively weak oxi-... 

The other Corey reagent, pyridinium dichromate (PDC), (C5H5NH )2Cr207 , dissolved in dimethylformamide (DMF) will oxidize allylic alcohols to a,)3-unsaturated aldehydes without oxidizing the aldehyde to the carboxylic acid. ... 

It would be more interesting and useful if the reaction could be made catalytic. Actually, catalytic decarbonylation reaction was found to be possible by using chlorocarbonylbis(triphenylphosphine) rhodium (XII) (26). This complex is reasonably stable, and more importantly it is four-coordinated and coordinatedly unsaturated, so that it may expand to a six-coordinated complex by the oxidative addition of acyl halides or aldehydes. The oxidative addition of methyl iodide to similar complexes was reported by Heck (5). 

In the case of X = CO2H (Scheme 41) the product of the rearrangement is an unsaturated a-hydroxy-carboxylic acid which may be converted to an aldehyde by oxidation, thus allowing a stereoselective synthesis of (3,7-unsaturated aldehydes (Scheme 43). °... 

To date, few reports on synthetic enzymatic oxidations of aldehydes have been published. Preparative applications reported include bioconversions of natural products such as retinal (Fig. 16.4-1 A) and various aliphatic and unsaturated aldehydes (Fig. 16.4-1 B). A broad range of aromatic acids can be obtained from their corresponding aldehydes (Fig. 16.4-1 C). Another reported reaction type is the production of olefins from aldehydes by oxidative removal of formic acid from the substrate (Fig. 16.4-1 D). 

Figure 16.4-1. Selected enzymatic oxidations of aldehydes. A oxidation of complex natural products such as retinal B oxidation of aliphatic and a,P-unsaturated aldehydes C oxidation of (hetero)arylic aldehydes D oxidative cleavage of the aldehyde-carbon atom yielding terminal alkenes.

Let us consider three types of interaction between (1) adsorbed hydrocarbon ion-radicals and oxygen of the gas phase (2) adsorbed oxygen and hydrocarbon of the gas phase (oxygen adsorbed both with and without dissociation) (3) adsorbed oxygen and adsorbed hydrocarbon. Saturated aldehydes and acids containing less carbon atoms than in the molecule of initial hydrocarbon, as well as carbon dioxide and water, are formed in the first case. The second type of interaction yields unsaturated aldehydes, olefine oxides, carbon monoxide, carbon dioxide, and water for the oxidation of unsaturated hydrocarbons and saturated aldehydes, carbon dioxide, carbon monoxide, and water for the oxidation of saturated hydrocarbons. The third type of reaction gives... 

Detailed review of studies on the auto- and catalytic-oxidation of unsaturated aldehydes in the liquid phase may be found in [2,9], Here we just note the main specific feature of the unsaturated aldehydes oxidation, briefly cited in Section 5.2. It implies that the free-radical chain process of the aldehyde group oxidation stimulates undesirable reactions, including the copolymerization of aldehyde with oxygen through the aldehyde s double bond, and in some cases also the copolymerization of the reaction products, the unsaturated acids and peroxyacids with oxygen. The oxidation reactions of unsaturated aldehydes are defined as the multicentered chain processes with two types of reaction centers acyl monomeric and polyperoxide free radicals. 

POM-pillared LDHs have also been used for the oxidation of alkenes to epoxides with H2O2 alone or more efficiently assisted by bromide. As previously discussed, a,(3-unsaturated ketones can be readily epoxidized with the help of normal LDH catalysts. So far, however, the epoxidation of nonactivated olefins requires the use of POM-LDH catalysts. For example, cyclohexene is selectively epoxidized using Ni2Al-SiWii04o" as catalyst, with the combination of oxygen and aldehyde as oxidant (487,488). The epoxidation of 2-hexene and 3-methylstyrene was also investigated by the same authors. 

PA Conjugated carbonyl unsaturations, products of photooxidation, TiOa, derivatives of anthraquinone, copper compounds Amines, GO, hydrc en, hydrocarbons, carbos lic acids, pyrroles, crosslinks Amines, CO, CO2, acids, ammonia, water, aldehydes, p oxides... 

The transformation of saturated ketones into a,/8-unsaturated ketones is often carried out by the introduction of an a-seleno-substituent, followed by oxidation and elimination. An alternative method for selenation of ketones (and esters) has been described wherein the lithium enolate reacts with selenium metal (rather than a selenyl halide) followed by methyl iodide (Scheme 29). Yields are comparable to the classical method. Phenylselenyl chloride reacts with enamines derived from aldehydes to give a-phenylselenoaldehydes, and hence o(,/3-unsaturated aldehydes by oxidative elimination [equation (21)]. ... 

A method for the preparation of amides from aldehydes by oxidation of the corresponding cyanohydrin is described this reaction is subject to the same selectivity as the previously reported method of conversion of aldehydes into esters the aldehyde must be aromatic or ajS-unsaturated to permit allylic oxidation of the cyanohydrin to the a-oxonitiile, which reacts with amines in situ to give the derived amides. 

The 5-oxohexanal 27 is prepared by the following three-step procedure (1) 1,2-addition of allylmagnesium bromide to an a, / -unsaturated aldehyde to give the 3-hydroxy-1,5-diene 25, (2) oxy-Cope rearrangement of 25 to give 26, and (3) palladium catalyzed oxidation to afford 27. The method was applied to the synthesis of A -2-octalone (28), which is difficult to prepare by the Robinson annulation[25]. 

The methyl enol ether 37 is oxidized to the a,/3-unsaturated aldehyde 39 via hemiacetal 38. Unsaturated aldehyde 39, elongated one carbon from the aldehyde 36, is prepared by the Wittig reaction of 36 to give 37, and application of this reaction[ 88]. 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

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