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6659440 
Journal Article 
Radical cation cycloaddition reactions of 2-vinylbenzofurans and 2-vinylfurans by photoinduced electron transfer 
Botzem, J; Haberl, U; Steckhan, E; Blechert, S; , 
1998 
Yes 
Acta Chemica Scandinavica
ISSN: 0904-213X
EISSN: 1902-3103 
BLACKWELL MUNKSGAARD 
FREDERIKSBERG C 
175-193 
WOS:000071860500006 
2-Vinylbenzofuran (2a) and 2-isopropenylbenzofuran (2b) can be successfully employed in cycloaddition reactions involving photoinduced electron transfer with 1,3-cyclohexadienes 4, styrenes 5 and acyclic 1,3-dienes 6, yielding [4 + 21]-and/or [2 + 2]-cycloadducts. 2,4,6-Tri(4-melhoxyphenyl)pyrylium telrafluoroborate (la) acts as an efficient sensitizer. Products are benzofuryl substituted cyclobutanes, 1,2,3,4-tetrahydrodibenzofurans, 2-benzofuryl bicyclo[2.2.2]octenes, and benzofuryl substituted cyclohexenes. Of 2-vinylfurans, only the 5-bromo substituted derivative 3 reacted with 1,3-cyclohexadiene. The 2-vinylbenzofurans behave like styrenes in these photoinduced cycloaddition reactions mostly generating intermediate cyclobutyl radical cations. 1,3-sigmatropic C- and H-shifts taking place at the radical cation stage are likely in these reactions. The mechanisms are discussed in detail, supported by quantum chemical calculations.