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The electron transfer photoreaction between 9,10-dicyanoanthracene (DCA) and (E)-3,7-dimethylocta-2,6-dien-1-ol (geraniol, (E)-1) in dichloromethane produces mainly cis-2-(2-propenyl)-trans-5-methylcyclopentanemethanol, cis,trans-3, whereas irradiation of acetonitrile solutions of 1,4-dicyanobenzene (DCB) and (E)-1 forms mainly two trans-fused 3-oxabicyclo[3.3.0]octanes (4, R ) H; 5, R ) p-C 6 H 4 CN). Analogous results are observed in the photoreaction of farnesol ((E,E)-2) with DCB in the presence of phenanthrene as cosensitizer. The photoreaction of DCB with 1 or 2 has sufficient driving force (∆G ) -0.7 eV in acetonitrile) for the generation of solvent-separated radical ion pairs (SSRIPs); in contrast, the marginal driving force (∆G ≈ 0 eV) of the DCA sensitized reaction allows only the formation of contact radical ion pairs (CRIPs). The resulting radical cations react by fivecenter C-C cyclization, yielding di-tertiary, 2,R-bifunctional methylidenecyclopentyl radical cations, cis-or trans-B •+ . Subsequently, CRIPs undergo rapid back electron transfer and intramolecular hydrogen transfer, generating product 3. The radical cations, trans-B •+ , of SSRIPs undergo a second cyclization by intramolecular nucleophilic capture, generating 3-oxabicyclo[3.3.0]oct-6-yl free radicals, trans-C • .

Photoinduced electron transfer from 7-methylenenorbomadiene, MN, and 7-methylenequadricyclane, MQ, to an excited sensitizer/acceptor in the presence of methanol generates products of several structure types. All products require nucleophilic capture of the radical cations, MN,+ and MQ'+, by methanol, followed by rapid rearrangements of the resulting free radicals to C' as the key intermediate. The short lifetime of the primary products of capture is ascribed to the allylic nature of their C4-C5 bonds. The stereochemistry of the methoxy groups in the products indicates that the nucleophile attacks MQ*+ exclusively from the "exo" face ("backside" attack), whereas MN*+ shows, in addition, a limited degree of attack from the "endo" face.

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