Relative migratory aptitudes of hydrogen, benzoyl, 4-methoxyphenyl and 4-nitrophenyl groups in some unsaturated carbenes (vinylidenes)

([5-C-13]Tetrazol-5-yl)methyl ketones were prepared and subjected to oxidative fragmentation induced by lead tetraacetate. The resulting intermediate [1-C-13]-3-oxoprop-1-en-1-ylidenes rearrange, depending on the relative migratory aptitudes of the benzoyl group and the ligands R, either to [3-C-13]prop-2-yn-1-ones or to [2-C-13]prop-2-yn-1-ones or to mixtures of the two isomers. The H-1 and/or C-13 NMR spectra of the products allow the three cases to be distinguished. The relative migratory aptitudes were found to be H > PhCO, 4-MeOC6H4>4-O2NC6H4. (C) 2001 Elsevier Science Ltd. All rights reserved.