Radicals transannular rearrangements

The electron-transfer-induced chemistry of bicyclobutane systems offer a rich variety of reactions. Irradiation of naphthalene in the presence of 46 resulted in rapid fluorescence quenching without rearrangement. In contrast, irradiation with either 1-cyanonaphthalene or 9,10-dicyanoanthracene in solutions containing derivatives of 46 resulted in product formation. The product distribution obtained under electron-transfer conditions is compatible with radical cations of structure type 46 +, which is firmly established by ESR and CIDNP results. Nucleophilic capture of the 1,2,2-trimethyl derivative, 50", led to cleavage of the transannular bond. The initial eapture is followed by net addition, producing 51, or dehydrogenation, yielding 52 [179]. 

The most thoroughly studied bicyclobutane system is a bridged derivative, tricy-clo[4.1.0.0 ]heptane (Moore s hydrocarbon, 47), which has revealed many facets of radical cation reactivity. Nucleophilic solvents (CH3OH, H2O) or ionic nucleophiles (CN ) capture 47 +, leading to products formally derived by addition across the transannular bond (53, 54, 55). Significantly, each product is derived by backside attack, as indicated clearly for the monomethyl derivative (54, 55, R = CH3) [180], In the absence of nucleophiles, a (dimeric) rearrangement product (57) was obtained (Scheme 2) [180, 181]. 

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