Vinylindoles, cycloaddition radical cation initiated

The same group studied the radical cation cycloaddition of 2-vinylbenzofti-rans with various alkene and diene compounds initiated by photoinduced electron transfer. Depending on the unsaturated compound used, yields up to 60% were feasible. In contrast to 2-vinylindoles, 2-vinylbenzofurans prefer to react as die-nophiles, very similar to styrenes [82]. 

In the electron-transfer-sensitized reaction of the 2-vinylindole 27 with dienes it has been found that the indole rather than the diene usually [41c], although not always [41b], becomes the diene partner in the 2-1-4 cycloaddition reaction styrenes also add to 27 in this manner and the initial adducts are further oxidized to the carbazole 28 under the reaction conditions (Scheme 11) [41c]. Formation of the indole radical cation and its attack on the styrene to give intermediate 29 explains the regioselectivity observed. 

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