Ketene Reactions with the Aminoxyl Radical TEMPO:  Preparative, Kinetic, and Theoretical Studies

• Published in: Journal of organic chemistry Vol. 66; no. 8; pp. 2611 - 2617
• Main Authors: Allen, Annette D, Cheng, Bernice, Fenwick, Michael H, Givehchi, Babak, Henry-Riyad, Huda, Nikolaev, Valerij A, Shikhova, Elena Aleksadrovna, Tahmassebi, Daryoush, Tidwell, Thomas T, Wang, Silas
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 20.04.2001; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; REARRANGEMENT; VINYLKETENE; NITROXIDE; MECHANISM; SPECTROSCOPY; PHOTOCHEMICAL CLEAVAGE; AB-INITIO; REACTIVITY; CHEMISTRY; PHOTOLYSIS
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo0011336

Tetramethylpiperidinyloxy (TEMPO, TO•) reacts with ketenes RR1CCO generated by either Wolff rearrangement or by dehydrochlorination of acyl chlorides to give products resulting from addition of one TEMPO radical to the carbonyl carbon and a second to the resulting radical. Reactions of phenylvinylketenes 4b and 4f, phenylalkynylketene 4c, and the dienylketene AcOCMeCHCHCHCMeCO (11) occur with allylic or propargylic rearrangement. Even quite reactive ketenes were generated as rather long-lived species by photochemical Wolff rearrangement in isooctane solution, characterized by IR and UV, and used for kinetic studies. The rate constants of TEMPO addition to eight different ketenes have been measured and give a qualitative correlation of log k 2(TEMPO) = 1.10 log k(H2O) −3.79 with the rate constants for hydration of the same ketenes. Calculations at the B3LYP/6-311G**//B3LYP/6-311G** level are used to elucidate the ring opening of substituted cyclobutenones leading to vinylketenes and of 2,4-cyclohexadienone (17) forming 1,3,5-hexatrien-1-one (18).