Acyl cyanides decarbonylation

Wilkinson s catalyst has also been reported to decarbonylate aromatic acyl halides at 180°C (ArCOX ArX). This reaction has been carried out with acyl iodides, bromides, and chlorides. Aliphatic acyl halides that lack an a hydrogen also give this reaction, but if an a hydrogen is present, elimination takes place instead (17-16). Aromatic acyl cyanides give aryl cyanides (ArCOCN—> ArCN). Aromatic acyl chlorides and cyanides can also be decarbonylated with palladium catalysts. °... 

Decarbonylation of acyl cyanides.9 Aromatic acyl cyanides, which are easily obtained by oxidation of cyanohydrins with /-butyl hydroperoxide catalyzed by RuC12[P(C6H5)3]3, undergo decarbonylation to nitriles in high yield when heated in the presence of Pd(0). 

This duality is entirely analogous to that found in the decarbonylation of aroyl or acyl cyanides by [Pd(PPh3)4] as shown in equations (1) and (2). ... 

However, in other instances, postelimination reactions can change the nature of the products. The main difficulty arises from the readdition of the alkene initially produced to the hydrido complex. This can result in isotopic scrambling or isomerization of the alkene upon reelimination. The formation of internal alkene products from the [Pd(PPh3)4]-catalyzed decarbonylation of acyl cyanides (equation 2) may also arise from postelimination reactions between the alkene and [PdH(CN)(CO)(PPh3) ] initially formed. The importance of this reaction in isomerizing the anti-Bredt alkenes formed by the catalytic decarbonylation of 3-chlorocarbonyltricyclo[5.3.1.0 ]iindecane is shown in Scheme 3. 

Murahashi, S., Naota, T., Nakajima, N. Palladium-catalyzed decarbonylation of acyl cyanides. J. Org. Chem. 1986, 51,898-901. 

The palladium-catalyzed decarbonylation of aromatic acyl cyanides proceeds at 120 °C to give the corresponding nitriles in excellent yield. Since acyl cyanides are readily prepared by the ruthenium-catalyzed oxidation of cyanohydrins with BuKDOH this represents a good method for the conversion of aldehydes to nitriles under mild conditions (Scheme 29). 

Acyl cyanides undergo oxidative addition to transition metals like rhodium and palladium, leading to catalytic decarbonylation [108,109]. This process is also involved in the catalytic acylcyanation of terminal alkynes [110]. 

Cyano-3,6-dimethyl-4//-pyran was isolated in 60% yield in attempts to generate a./S-unsaturated acyl cyanide by the substitution of H2C=C(Me)COCl with CuCN to give H2C=C(Me)COCN and CuCl, but the structure of the 4//-pyran is not well explained by the postulated (83TL2847 86JOC1199) mechanism. An alternative route involving initial decarbonylation (H2C=C(Me)COCl — H2C=C(Me)Cl + CO) and subsequent cycloaddition leading to intermediate 90 appears to be a more acceptable version. 

The reaction of carboxylic acid chlorides with low-valent metal complexes leads to the formation of acyl complexes, which can undergo decarbonylation to give a-bonded metal alkyls, alkenyls, or aryl complexes. This decarbonylation has been used to synthesize aiylsilanes from aryl acid chlorides in the presence of nickel(0) or palladium(0) complexes as catalysts. Similarly, acyl cyanides undergo decarbonylation with palladium(O) complexes to afford nitriles or alkenes, depending on the substrate. ... 

Murahashi S, Naota T, Nakajima N (1986) Palladium-catalyzed decarbonylation of acyl cyanides. J Org Chem 51(6) 898-901. doi 10.1021/jo00356a029... 

Decarbonylation of acyl cyanides has also been known since Blum reported a rhodium-catalyzed reaction in 1967 (Eq. (6.16)) [35]. Later, this reaction was significantly improved by using a palladium-based catalyst [36]. 

Analogous decarbonylation reactions were observed with acyl halides [18], esters [19], acyl cyanides [20], thioesters [21], selenoesters [21b], acylphospho-nates [22], and even ketones (preceding chapters). Acid anhydrides underwent a fragmentation reaction upon treatment with a nickel catalyst to afford alkenes,... 

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