Cyclopentane ring formation in the cycloaddition reaction of 3-alkenyl radicals to radicophilic olefins
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Regioselective additions of 3-alkenyl radicals (10 and 20) to electron deficient olefinic bonds (7 and 17), followed by intramolecular 5- exo-cyclization and repeated addition to radicophilic double bonds were investigated and combined into a sequence of reactions for the preparation of cyclopentane derivatives (9 and 19). High regioselectivity of 3-alkenyl radical (10) addition to the electron deficient olefinic bond (7) as well as of 5-exo -cyclization of intermediary 5-hexenyl type radical (11), was achieved. The fate of intermediary cyclopentylmethyl radicals (22 and 27) depends on the nature of substituents attached to radical carbon. In case of alkyl groups (22), the nucleophilic reactivity of radical intermediates was increased and an intermolecular addition reaction occurred with the formation of a new C-C bond. However, in case of aryl groups, mesomeric stabilization of the radical (27) suppress the addition reaction to the radicophilic olefinic bond, even when the latter was ...used in excess, in these cases only hydrogen abstraction takes place. © 1990.