| Abstract
| - Aryl radical cyclization in N-phenyl, N-benzyl, and N-phenethyl enaminone esters 1a−f was studied.N-Benzyl and N-phenethyl enaminones afforded 5-exo and 6-exo cyclization products, respectively,but radical cyclization did not occur in N-phenyl enaminones. The rate constants for the 5-exo and6-exo cyclization processes in secondary enaminones were estimated as being on the order of 107s-1 at 353 K; since DNMR experiments showed the rate constant for rotation around the enaminoneC3−N bond to be on the order of 104 s-1 at this temperature, the initial enaminone configurationis maintained throughout the cyclization process. PM3 calculations suggested that the nonoccurrenceof endo and 4-exo cyclizations is due to the corresponding transition structures involving significantdistortion of the conjugated enaminone system.
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