Tsuji-Wilkinson decarbonylation

In the laboratory of F.E. Ziegler, the synthesis of the core nucleus of FR-900482 was accomplished. In the final stages of the synthetic effort, the removal of the formyl group from the C7 quaternary center was necessary. The authors chose the Tsuji-Wilkinson decarbonylation protocol to effect the transformation. The 1,3-diol functionality was protected as the acetonide prior to the decarbonylation. Usually the rate of decarbonylation is slowest for aldehydes that have the formyl group attached to a quaternary carbon, so it was necessary to use more than two equivalents of the catalyst to effect the decarbonylation at the reflux temperature of xylene. 

The isodaucane sesquiterpene (+)-aphanamol I was synthesized in the laboratory of B. Wickberg using the DeMayo cycloaddition as the key step. The required starting material 3(S)-isopropyl-1-methylcyclopentene was prepared by the Tsuji-Wilkinson decarbonylation of the corresponding a,p-unsaturated aldehyde. 

One of the first reports concerned with the decarbonylation of a,P-unsaturated aldehydes by means of the Wilkinson complex was published by Tsuji and Ohno in 1965 (Scheme 8.2) [6]. Already these investigations illustrated the high temperatures mostly applied. It should be remembered that enals are typical products emerging in the hydroformylation of 1,3-butadienes. Moreover, the reaction proceeded also with saturated aldehydes to give alkanes. 

Wilkinson s catalyst and chlorocarbonylbis(triphenylphosphine)rhodium [or iridium] can catalyze the thermal decarbonylation of aromatic acid halides to aryl halides. An intermediate Rh(III) hydride is involved in the reaction (Suggs, 1978). For aliphatic acid halides, subsequent elimination of HX frequently occurs from the generated alkyl halide (Ohno and Tsuji 1968 Blum et al., 1%7, 1971 Strohmeier and Pfohler, 1976). 

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