| Abstract
| - Tetramethylpiperidinyloxy (TEMPO, TO•) reacts with ketenes RR1CCO generated by eitherWolff rearrangement or by dehydrochlorination of acyl chlorides to give products resulting fromaddition 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 AcOCMeCHCHCHCMeCO (11) occur with allylic or propargylic rearrangement. Even quite reactiveketenes were generated as rather long-lived species by photochemical Wolff rearrangement inisooctane solution, characterized by IR and UV, and used for kinetic studies. The rate constants ofTEMPO addition to eight different ketenes have been measured and give a qualitative correlationof log k2(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 openingof substituted cyclobutenones leading to vinylketenes and of 2,4-cyclohexadienone (17) forming1,3,5-hexatrien-1-one (18).
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