Tests for Free-Radical Intermediates in the Decarbonylation of Aldehydes by Tris(triphenylphosphine)chlororhodium(I)

Article abstract of DOI:10.1021/jo01290a023

Wilkinson's catalyst was reacted with phenylacetaldehyde (5h), phenylacetaldehyde-d (5d), p-methylphenylacetaldehyde (6), citronellal (7), and exo- and endo-5-norbornene-2-carboxaldehyde (10x and 10n).The decarbonylation of mixtures of 5h and 5d shows an isotope effect (kH/kD) of 1.86 +/- 0.07.No H-D crossover is observed when a mixture of 5d and 6 is reacted with 1.The reaction of citronellal (7) gives only 2,6-dimethyl-2-heptene. 10x gives norbornene, and 10n gives nortricycline; no crossover between the two systems is observed.These observations are consistent with concerted processes, intramolecular in aldehyde, for each step in the overall decarbonylation reaction; free- radical intermediates are excluded.