Heptafulvenone, Vinylketene, Butadienylketene, and Allenylketene − Facile Generation, Observation, and Radical Reaction with TEMPO

Abstract

Heptafulvenone (1), vinylketene (11), 1,3-butadienylketene [(E)-15], and allenylketene (21) have been prepared by reaction of the corresponding acyl chlorides with 1,8-bis(dimethylamino)naphthalene as long-lived species in solution at room temperature, and their ketenyl IR bands observed under these conditions for the first time, at 2101, 2118, 2111, 2117 cm−1, respectively. These unsaturated ketenes react with tetramethylpiperidinyloxyl (TEMPO, TO·) with initial attack at the carbonyl carbon giving delocalized radicals which give from 1 a mixture of the ring contracted o-, m-, and p-formylbenzoates O=CHC6H4CO2T (6) and the bis(cycloheptatrienyl) dimer 7. The products from 11, (E)-15, and 21 are the bis(TEMPO) adducts (E,Z)-TOCH2CH=CHCO2T (12), (E,E)-TOCH2CH=CHCH=CHCO2T (17), and (E,Z)-CH2=C(OT)CH=CHCO2T (22), respectively.