Photochemical Wolff rearrangements in alkane solvents of the 6-diazo-2, 4- cyclohexadienones 4 and 13-15 give pentafulvenone (1), 2, 3-benzopentafulvenone (2), dibenzopentafulvenone (3), and 2, 4-di-tert-butylpentafulvenone (16), as identified by conventional UV and IR spectroscopy. Reactions of these fulvenyl ketenes with tetramethylpiperidinyloxyl (TEMPO) proceed by addition of TEMPO to the carbonyl carbon ...