“Competitive reaction pathways for o-amidoaryl radicals: 1,5 or 1,6 hydrogen transfer versus nuchleophilic

REY, VALENTINA; PEÑÉÑORY, ALICIA B

Los Cocos,Córdoba, Argentina

Conferencia; 9° Conferencia Latinoamericana de Fisico Química Orgánica (CLAFQO); 2007

CLAFQO

We have described for the first time the reactivity of sulfur-centered nucleophiles such as thiourea anion (1, -SCNH(NH2)),1 and thioacetate anion (2, MeCOS-)2 in photoinduced aromatic radical nucleophilic substitution as a “one-pot” method for the synthesis of several sulfur aromatic compounds from moderate to good yields. This reaction provides a very good alternative to introduce a sulfur functionality in aryl compounds by ipso substitution of an adequate leaving group. To apply this methodology to the synthesis of benzotiazoles, we have studied the reactivity of o-iodoanilides (3) with anions 1 and 2 in photoinduced reactions in DMSO, as a strategy to replace the iodide by a sulfur anion. Further reaction of this anion with the carbonyl group would render the desired heterocycle. These reactions proceed with an initial photoinduced electron transfer (PET) from 1 to the iodide 3, followed by fragmentation of the corresponding radical anion to finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. replace the iodide by a sulfur anion. Further reaction of this anion with the carbonyl group would render the desired heterocycle. These reactions proceed with an initial photoinduced electron transfer (PET) from 1 to the iodide 3, followed by fragmentation of the corresponding radical anion to finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. radical nucleophilic substitution as a “one-pot” method for the synthesis of several sulfur aromatic compounds from moderate to good yields. This reaction provides a very good alternative to introduce a sulfur functionality in aryl compounds by ipso substitution of an adequate leaving group. To apply this methodology to the synthesis of benzotiazoles, we have studied the reactivity of o-iodoanilides (3) with anions 1 and 2 in photoinduced reactions in DMSO, as a strategy to replace the iodide by a sulfur anion. Further reaction of this anion with the carbonyl group would render the desired heterocycle. These reactions proceed with an initial photoinduced electron transfer (PET) from 1 to the iodide 3, followed by fragmentation of the corresponding radical anion to finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. replace the iodide by a sulfur anion. Further reaction of this anion with the carbonyl group would render the desired heterocycle. These reactions proceed with an initial photoinduced electron transfer (PET) from 1 to the iodide 3, followed by fragmentation of the corresponding radical anion to finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. 1, -SCNH(NH2)),1 and thioacetate anion (2, MeCOS-)2 in photoinduced aromatic radical nucleophilic substitution as a “one-pot” method for the synthesis of several sulfur aromatic compounds from moderate to good yields. This reaction provides a very good alternative to introduce a sulfur functionality in aryl compounds by ipso substitution of an adequate leaving group. To apply this methodology to the synthesis of benzotiazoles, we have studied the reactivity of o-iodoanilides (3) with anions 1 and 2 in photoinduced reactions in DMSO, as a strategy to replace the iodide by a sulfur anion. Further reaction of this anion with the carbonyl group would render the desired heterocycle. These reactions proceed with an initial photoinduced electron transfer (PET) from 1 to the iodide 3, followed by fragmentation of the corresponding radical anion to finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. finally afford the o-amidoaryl radical 4. The latter radical have three competitive reaction pathways depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. depending on the structure of the a-carbonyl moiety (Scheme 1): a) R = CH3, coupling with 1 to render the thiolate anion 5; b) R = t-Bu, 1,6-hydrogen transfer, followed by a 1,4-aryl migration to afford an amidyl radical (6); and c) 1,5-hydrogen transfer to give a a-carbonyl radical (7). Evidences for the proposed mechanism will be discussed. for the proposed mechanism will be discussed. afford an amidyl radical (