The photoexcitation of a self-assembled M6L4-type coordination cage accommodating photochemically inert alkane guests (e.g., adamantane and cyclooctane) led to the regioselective oxidation of the guest within the cage. Under anaerobic conditions, the guest oxidation was accompanied by the stable radical formation as indicated by ESR spectrometry (g = 2.002) and change in solution color (from colorless to blue). These phenomena were shown to be characteristic of the self-assembled molecular systems: i.e., from the M6L4 supersetGn assembly, none of the components (M, L, or G) can be eliminated for the unusual oxidation and/or radical formation.

H-D exchange was observed in the methyl group during the formation of sulfones in the reaction of dimethyl sulfide-d 6 or thioanisole-R,R,R-d 3 with singlet oxygen in aprotic solvents. No exchange was observed in the sulfoxides obtained. The proton in the sulfones was shown to come from adventitious water, since the oxidation of C 6 H 5 SCH 3 in the presence of D 2 O lead to the formation of sulfones with monodeuteriation. The 16 O 2 -18 O 2 tracer study demonstrated no oxygen scrambling in the sulfones. All the results indicate that the sulfones are formed intramolecularly via an intermediate possessing one activated proton exchangeable with trace water, a suggested structure for which is S-hydroperoxysulfonium ylides (RS + (OOH)CH 2 -). Kinetic isotope effects (k H /k D ) 2-4) observed for methyl protons in the sulfone formation suggest that the rate-determining step is the intramolecular proton abstraction in the persulfoxides (RS + (OO -)CH 3 ) generating S-hydroperoxysulfonium ylides. The conversion of the ylide intermediates to sulfones is shown to be facile on the basis of PM3 theoretical calculations.

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The photochromic valence isomerization of the system norbornadiene (N)-quadricyclane (Q) has attracted much attention in the field of photochemical energy storage1 and, more recently, has been considered as the basis for an optical memory system.2 The energy-releasing conversion of Q to N can be achieved with high efficiency via a free-radical-cation chain reaction, initiated by chemical? electrochemical$ or photosensitized one-electron oxidations (eql).s The existence of two distinct radical cations,