TY - JOUR
T1 - Photoinduced electron-transfer, pyrolyses, and direct irradiation reactions of 2-methylenecyclobutanones
T2 - Regioselective bond cleavage depends on the substituents and the method of activation
AU - Ikeda, Hiroshi
AU - Tanaka, Futoshi
AU - Miyashi, Tsutomu
AU - Akiyama, Kimio
AU - Tero-Kubota, Shozo
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2004/3/26
Y1 - 2004/3/26
N2 - The regioselectivity of bond cleavage and the subsequent reactivity of 4-methylene-3,3-dimethyl-2,2-diphenylcyclobutan-1-one (5) and 4-isopropylidene-2,2-diphenylcyclobutan-1-one (6) in photoinduced electron transfer, pyrolysis, and direct irradiation reactions were investigated. Novel photoinduced electron-transfer rearrangements of 5 and 6 were found to occur through 1,4-diyl radical cations formed by C1-C2 cleavage of 5.+ and 6.+; that is, similarly to radical-cation Norrish type I cleavage, but in contrast to the diansyl derivative 1.+ corresponding to 5 .+, which gives an oxatetramethyleneethane (OTME)-type radical cation through C2-C3 cleavage. In contrast, solvent effects on the thermal rearrangement of 5 to 6 and theoretical calculations suggested the intervention of an OTME-type diradical intermediate 16.. formed by homolytic C2-C3 cleavage of 5. In direct photoreactions, 5 and 6 undergo [2+2] cycloreversion to give 1,1-diphenylethylenes and methyleneallenes, which are explained by both C1-C2 and C3-C4 cleavage. Consequently, the regioselectivity of 5 and 6 in bond cleavage and their reactivity strongly depend on the substituents and the method of activation.
AB - The regioselectivity of bond cleavage and the subsequent reactivity of 4-methylene-3,3-dimethyl-2,2-diphenylcyclobutan-1-one (5) and 4-isopropylidene-2,2-diphenylcyclobutan-1-one (6) in photoinduced electron transfer, pyrolysis, and direct irradiation reactions were investigated. Novel photoinduced electron-transfer rearrangements of 5 and 6 were found to occur through 1,4-diyl radical cations formed by C1-C2 cleavage of 5.+ and 6.+; that is, similarly to radical-cation Norrish type I cleavage, but in contrast to the diansyl derivative 1.+ corresponding to 5 .+, which gives an oxatetramethyleneethane (OTME)-type radical cation through C2-C3 cleavage. In contrast, solvent effects on the thermal rearrangement of 5 to 6 and theoretical calculations suggested the intervention of an OTME-type diradical intermediate 16.. formed by homolytic C2-C3 cleavage of 5. In direct photoreactions, 5 and 6 undergo [2+2] cycloreversion to give 1,1-diphenylethylenes and methyleneallenes, which are explained by both C1-C2 and C3-C4 cleavage. Consequently, the regioselectivity of 5 and 6 in bond cleavage and their reactivity strongly depend on the substituents and the method of activation.
KW - Bond cleavage
KW - Electron transfer
KW - Methylenecyclobutanone
KW - Photochemistry
KW - Regioselectivity
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U2 - 10.1002/ejoc.200300703
DO - 10.1002/ejoc.200300703
M3 - Article
AN - SCOPUS:4544255827
SP - 1500
EP - 1508
JO - Annalen der Pharmacie
JF - Annalen der Pharmacie
SN - 0075-4617
IS - 7
ER -