Nucleophilic aromatic substitution on ester derivatives of carcinogenic N-arylhydroxamic acids by aniline and N,N-dimethylaniline
作者:Michael Novak、Kanchugarakoppal S. Rangappa、Rebecca K. Manitsas
DOI:10.1021/jo00079a028
日期:1993.12
Decomposition of N-(pivaloyloxy)-2-(acetylamino)fluorene (1b) and N-(sulfonatooxy)-4-(acetylamino)-biphenyl (2a) in MeOH occurs predominately via N-0 bond cleavage to yield oxazoles (5, 6, 23), methoxy adducts (7,8,24,25,26), and rearrangement products (10b,11b,28). Minor ester methanolysis paths lead to the N-arylhydroxamic acids (9, 27). In the presence of 0.1 M aniline (3), 1b yields a number of adducts (14-18) identical to those previously obtained from the reaction of 3 with N-(sulfonatooxy)-2-(acetylamino)fluorene (1a). This occurs with no change in the rate constant for decomposition of 1b. At 0.1 M 3 all solvolysis products of 1b, except the rearrangement products 10 band 11b, are reduced below detectable levels. Similar results were obtained for 2a, which yields the adducts 30-35 in the presence of 3 and 36-38 in the presence of N,N-dimethylaniline (4). These results are consistent with a mechanism (Scheme V) in which the N-O bond heterolysis leads to a tight ion pair that can undergo internal return to yield the rearrangement products or diffusional separation to yield the free ion. The free nitrenium ion can be trapped by solvent or added nucleophiles. Both the N-acetyl-N-(4-biphenylyl)nitrenium ion (45) and the N-acetyl-N-(2-fluorenyl)nitrenium ion (48) react slowly enough with the solvent to undergo selective reaction with strong nucleophiles. Since 1a, 1b, and 2a span the reactivity range of the ester derivatives of the common N-arylhydroxamic acids which undergo N-O bond heterolysis in H2O, it appears that all of the carcinogenic esters will react with simple aromatic amines via an S(N)1 mechanism.