Decarbonylation of acyl halides

Acyl halides are intermediates of the carbonylations of alkenes and organic-halides. Decarbonylation of acyl halides as a reversible process of the carbo-nylation is possible with Pd catalyst. The decarbonylation of aliphatic acid chlorides proceeds with Pd(0) catalyst, such as Pd on carbon or PdC, at around 200 °C[109,753]. The product is a mixture of isomeric internal alkenes. For example, when decanoyl chloride is heated with PdCF at 200 C in a distillation flask, rapid evolution of CO and HCl stops after I h, during which time a mixture of nonene isomers was distilled off in a high yield. The decarbonylation of phenylpropionyl chloride (883) affords styrene (53%). In addition, l,5-diphenyl-l-penten-3-one (884) is obtained as a byproduct (10%). formed by the insertion of styrene into the acyl chloride. Formation of the latter supports the formation of acylpalladium species as an intermediate of the decarbonylation. Decarbonylation of the benzoyl chloride 885 can be carried out in good yields at 360 with Pd on carbon as a catalyst, yielding the aryl chloride 886[754]. 

Rhodium(I) complexes are effective reagents and/or catalysts for the decarbonylation of acyl halides and aldehydes 9 11,34,195,230,231,236). The compound Rh(PPh3)3Cl, especially, has received considerable attention. The first step in such reactions involves oxidative addition to Rh(I) of the organic molecule, exemplified by the following ... 

The four-coordinate alkyl complex, LNiI(C0)CH3, may coordinate with carbon monoxide to regenerate the five coordinate alkyl species, and this leads to insertion to form Ni-acyl complex. This complex, LNil (CO)(COCH3), can be cleaved either by water yielding acetic acid or by methanol to give methyl acetate. However, in the presence of high iodide concentration formation of acetyl iodide may predominate (29). This step is reversible and can lead to decarbonylation under low carbon monoxide partial pressure. Similar decarbonylations of acyl halides by nickel complexes are known (34). 

Decarbonylation of Acyl Halides Hydro-chloroformyl-elimination... 

Decarbonylation of acyl halides 7-20 Cleavage of Michael adducts 7-21 Deoxygenation of vic-diols 7-22 Cleavage of cyclic thionocarbonates 7-23 Deoxidation of epoxides 7-24 Desulfurization of episulfides 7-25 Reaction of a-halo sulfones with bases (Ramberg-Backlund)... 

While most of the above carbonylations are carried out at pressures greater than 40 atm (isocyanate and acetic acid formations are exceptions), decarbonylations are low pressure reactions. Decarbonylation of acyl halides catalyzed by (3P)2RhCOCl leads either to halides (65) (Reaction 19)... 

Cleavage of ethers Organoaluminum reagents, 202 Decarbonylation of acyl halides Tetrakis(triphenylphosphine)palla-dium(0), 289 Dehalogenation... 

The decarbonylation of acyl halides and aldehydes proceeds under mild conditions to give aryl halides ArX and arenes ArH with a stoichiometric amount of RhCl(Ph3P)3. At the same time, RhCl(CO)(Ph3P)2 is formed which is inactive at moderate temperatures, and the reaction is stoichiometric [245-248],... 

XXXI. Carbonylation of Olefins and Decarbonylation of Acyl Halides and Aldehydes... 

Thus, this reaction is a most facile and selective method of decarbonylation of aldehydes. The decarbonylation of acyl halides by using the complex (XI) was then tried, and again decarbonylation proceeded smoothly though it was necessary to warm the solution for complete decarbonylation. 

Recently Blum reported that chlorotris(triphenylphosphine) rhodium (XI) is an active catalyst for the decarbonylation of aroyl halides and showed several examples (2). But in this case too, the real catalyst seems to be chlorocarbonylbis(triphenylphosphine)rhodium (XII), which is formed in situ from XI by the stoichiometric reaction with acyl halides. Formation of alkyl halides by decarbonylation of acyl halides can be carried out by the Hunsdiecker reaction, but the reaction is unsatisfactory when applied to aroyl halides. Therefore, the decarbonylation reaction of aroyl halides by the rhodium complex is a new and useful means of introducing halogen onto the aromatic ring. 

Tsuji, J., Ohno, K. Organic syntheses by means of noble metal compounds. XXXI. Carbonylation of olefins and decarbonylation of acyl halides and aldehydes. Advances in Chemistry Series 1968, No. 70, 155-167. 

Tsuji, J. Other reactions of acylpalladium derivatives palladium-catalyzed decarbonylation of acyl halides and aldehydes. Handbook of Organopaiiadium Chemistry for Organic Synthesis 2002, 2, 2643-2653. 

The stoichiometric decarbonylation of acyl halides with RhCl(PPh3)3 illustrates the reductive elimination of an alkyl halide firom an octahedral Rh(III) intermediate ( q. 6.36), a reaction that can be useful in organic synthesis ... 

In addition to Pd-catalyzed decarbonylation, rhodium complexes catalyze the decarbonylation efficiently. In this section, decarbonylation of acyl halides and aldehydes using palladium catalysts is surveyed. ... 

B. PALLADIUM-CATALYZED DECARBONYLATION OF ACYL HALIDES AND ACID ANHYDRIDES... 

The first step of the decarbonylation of acyl halides is their oxidative addition to form acylpalladium halides, which undergo acyl-alkyl rearrangement to form aryl- or alkylpal-ladium halides. Finally, elimination of j8-hydrogen affords alkenes and HCl. When j8-phenylpropionyl chloride was heated at 200 °C with Pd catalyst, styrene was formed as the main product, accompaiued by a small amount of l,5-diphenyl-l-penten-3-one. The... 

Pd-catalyzed decarbonylation of acyl halides and aldehydes is summarized. The decarbonylation proceeds mainly using Pd on carbon as a catalyst at high tanperature. 

This type of reaction, which has been the subject of many studies because of its potential utilization in the decarbonylation of acyl halides, has also been investigated with the analogous iridium(I) complex. The reversibility of the carbonylation/decarbonylation process was first described by Heck and Breslow in 1960, 5 and work with a wide range of organic substrates has been... 

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