Alkenes, oxidative decarboxylation

Oxidative decarboxylation of acids to alkenes is often accompanied by alkene rearrangement. Lukas... 

In contrast, the sex pheromone of the female housefly is (Z)-9-tricosene, a hydrocarbon apparently formed by an oxidative decarboxylative process from a precursor aldehyde by an enzyme that requires NAD-PH and 02 and is apparently a cytochrome P450.140 Oxidative deformylation by a cytochrome P450 converts aldehydes to alkenes, presumably via a peroxo intermediate.117 Formation of an alkene by decarboxylation has also been proposed,141 but a mechanism is not obvious. 

Stannyl- (and -silyl-) carboxylic acids undergo oxidative decarboxylation with LTA under mild conditions to provide the corresponding alkenes. This represents an improvement on the well-known alkene-forming decarboxylation of acids with LTA, which requires thermtd or photochemical conditions, for example. The directing metal effect leads to improved yields and regioselectivity. However, stereo-specific alkene formation did not occur and this could imply free radical involvement or transmetallation (Pb for Sn) (stereochemistry ) followed by cation formation, see for example Scheme 27. 

The oxidative decarboxylation of aliphatic carboxylic acids is best achieved by treatment of the acid with LTA in benzene, in the presence of a catalytic amount of copper(II) acetate. The latter serves to trap the radical intermediate and so bring about elimination, possibly through a six-membered transition state. Primary carboxylic acids lead to terminal alkenes, indicating that carbocations are probably not involved. The reaction has been reviewed. The synthesis of an optically pure derivative of L-vinylglycine from L-aspartic acid (equation 14) is illustrative. The same transformation has also been effected with sodium persulfate and catalytic quantities of silver nitrate and copper(II) sulfate, and with the combination of iodosylbenzene diacetate and copper(II) acetate. ... 

A mild, but indirect, approach to oxidative decarboxylation involves a modification of the 0-acyl thiohydroxamate decarboxylative rearrangement (Section 5.4.6.1). An 0-acyl selenohydroxamate is photolyzed to give a noralkyl-2-pyridyl selenide which, after ozonolysis to the selenoxide, undergoes syn elimination to the alkene (equation IS). 

Sodiomalonic esters behave like organometalic reagents toward alkene oxides. Acid hydrolysis of the adduct accompanied by decarboxylation and lactonization furnishes a-substituted lactones in high yields. "y-Substituted y-butyrolactones result from sodiomalonic ester and substituted ethylene oxides. ... 

Another widely used decarboxylation procedure involves the use of lead tetraacetate. Depending on the nature of the substrate and the reaction conditions, this reagent may transform a carboxylic acid into an alkane or alkene, or into the respective acetoxy derivative (Scheme 2.144). The most favorable conditions for alkane formation utilize a good hydrogen donor as the solvent. Usually this transformation is carried out as a photochemically induced oxidative decarboxylation in chloroform solution, as is exemplified in the conversion of cyclobutanecarboxylic acid in cyclobutane.In contrast, the predominant formation of alkenes occurs in the presence of co-oxidants such as copper acetate. ... 

In the case of vicinal dicarboxylic acids, the interaction with lead tetraacetate in the presence of co-oxidants (O2 or Cu " ) invariably leads to the formation of an alkene. The decarboxylation of vicinal dicarboxylic acids is an especially... 

See [6]. The following reaction types have been listed (a) Geometric isomerization of alkenes (b) Allylic [1,3] hydrogen shift (c) Cycloaddition of alkenes. Dimerization, Tri-merization. Polymerization (d) Skeletal rearrangments of alkenes and methathesis (e) Hydrogenation of alkenes (f) Additions to alkenes (g) Additions to C = X (h) Aliphatic substitutions (i) Aromatic substitution (j) Vinyl substitution (k) Oxidation of alkenes (1) Oxidation of alcohols (m) Oxidation of arenes (n) Oxidative decarboxylation (o) Oxidation of amines (p) Oxidation of vinylsilanes and sulfides (q) Oxidation of benzal-dehyde (r) Dehydrogenations. 

Because oxidative decarboxylation of carboxylic acids by lead tetraacetate depends on the reaction conditions, the co-reagents, and the structures of the acids, a variety of products such as acetate esters, alkanes, alkenes, and alkyl hahdes can be obtained. Mixed lead(IV) carboxylates are involved as intermediates as a result of their thermal or photolytic decomposition decarboxylation occurs and alkyl radicals are formed. Oxidation of alkyl radicals by lead(IV) species gives carbocations a variety of products is then obtained from the intermediate alkyl radicals and the carbocations. Decarboxylation of primary and secondary acids usually affords acetate esters as the main products (Scheme 13.41) [63]. 

Cupric acetate (anhydrous) markedly catalyzes the oxidative decarboxylation of carboxylic acids by lead tetraacetate to alkenes 7... 

Oxidative decarboxylation (1, 554-557 2, 235-237). Cupric acetate, Cu(0Ac)2.H20, markedly catalyzes decarboxylation of primary and secondary acids, and in this case alkenes, rather than alkanes, are formed in good to excellent yield, for example ... 

Oxidative decarboxylation of acids to alkenes is often accompanied by alkene rearrangement. Lukas J. Goossen of the Max-Planck-lnstitut, Muhlheim, has found (Chem. Commun. 2004, 724) that in situ activation of the acid with phthalic anhydride and inclusion of the bis phosphine DPE-Phos substantially slow alkene isomerization, which can be essentially eliminated by running the reaction to only 80% conversion. Both linear and branched carboxylic acids work well. 

The last stages are shown below. The ketone is protected, and the alkene oxidized to a carbonyl group by ozonolysis (Chapter 19). The diester can be cyclized by a Claisen ester condensation (Chapter 26). The stereogenic centres in the ring are not affected by any of these reactions so a trans ring junction must result from this reaction. After ester hydrolysis, HCl decarboxylates the product and removes the protecting group. 

Fig. 6.32 Structures of P450 peroxygenases. A comparison between the fatty acid complexes of P450 OleT (panel a) (PDB 4L40) and the related BSp (panel b) (PDB 1IZO). Both enzymes bind the substrate in similar manner, and key interactions occur between a conserved active site arginine residue (Arg245) and the fatty acid carboxylate moiety, as shown for OleT in panel C. P450 BSp catalyzes predominantly fatty acid P-hydroxylation, while the OleT enzyme catalyzes oxidative decarboxylation of its long-chain fatty acid substrates to produce the n-1 terminal alkenes [574, 575, 577]...

An electrochemical oxidative decarboxylation in combination with an ester enolate Claisen rearrangement was reported by Wuts et al. (Scheme 5.2.26) [51]. A variety of allylic esters such as 97 was subjected to an Ireland-Qaisen rearrangement, and the resulting acids (98) obtained were submitted to electrolytic decarboxylation in a divided cell to afford ketals 99. The use of the divided cell was necessary to suppress side reactions such as alkene reduction. 

Other reactions that involved [Mn(TNH2PP)Cl MWCNT] as catalytic nanoreactor are the oxidation with sodium periodate of 2-imidazolines in MeCN [174] and the oxidative decarboxylation of a-arylcarboxylic acids with sodium periodate [175] (Scheme 14.8 a,b). On the other hand, iron(lll) me o-tetra(2-chlorophenyl)porphyrin, coordinated to hydroxyl-functionalyzed MWCNTs, catalyzed the oxidation of alkanes, alkenes, and sulfides using tetrabutylammo-nium peroxomonosulfate (BU4NHSO5) as oxygen source [176] (Scheme 14.8c). 

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