Decarbonylation of Aldehydes and Related Compounds

Decarbonylation of aromatic aldehydes proceeds smoothly[71], Terephthalic acid (86), commercially produced by the oxidation of p-.xylene (85), contains p-formylbenzoic acid (87) as an impurity, which is removed as benzoic acid (88) by Pd-catalyzed decarbonylation at a high temperature. The benzoic acid produced by the decarbonylation can be separated from terephthalic acid (86) based on the solubility difference in water[72]. 

The cyano ketone 89 is converted into the nitrile 90 by heating at 140 C with Pd(Ph3P)4[73,74]. The a-lcetophosphonate 91 is decarbonylated with PdMe2(PMePh2)2 complex to give the phosphonate 92[75]. 

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The cychzation of pent-4-enals and related compounds to cyclopentanones is catalyzed by [RhCl(PPh3)3] in a reaction that involves oxidative addition of the -CHO group to the rhodium(I) catalyst. This reaction has much in common with the decarbonylation that most aldehydes undergo in the presence of this catalyst (see Decarbonylation Catalysis). 

The radical reduction of acyl halides and related compounds, such as acyl chal-cogenides, to aldehydes may find significance for primary, vinyl, and aromatic acyl radicals whose decarbonylation rates are significantly slower than those of the corresponding secondary and tertiary radicals [6], In practice, however, this method is restricted to substrates which have serious incompatibilities with more traditional methods. 

Tsuji, J., Ono, K., Kajimoto, T. Organic syntheses with noble metal compounds. XX. Decarbonylation of acyl chloride and aldehyde catalyzed by palladium and its relation with the Rosenmund reduction. Tetrahedron Lett. 1965, 4565-4568. 

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