Adamantylideneadamantane- 1,2-dioxetane

In the TPP+BF4 -sensitized photooxygenation of 21, leading to the corresponding thermally stable 1,2-adamantylideneadamantane dioxetane, 23, direct evidence for the chain electron-transfer reaction was achieved by quenching experiments, ns laser flash photolysis, and cyclic voltammetric studies [185]. 

The electrolysis of adamantylideneadamantane solutions affords the radical cation, which can add molecular (triplet) oxygen to give the peroxide radical anion, which can react with adamantylideneadamantane to give the 1,4-diradical and another molecule of adamantylideneadamantane radical cation. The latter reacts with oxygen, to continue the chain of the reaction, while the former cyclizes to the corresponding 1,2-dioxetane (Scheme 18) (81JA2098). 

Cycloaddition reactions can occur with retention of configuration in the pseudoexcitation band (Sect 1.1) whereas [2jt H-2jtJ reactions are symmetry-forbidden in the delocalization band. Experimental evidence is available for the stereospecific [2-1-2] cycloaddition reactions between A and olefins with retention of configuration (Scheme 14) [82]. A perepoxide intermediate was reported to be trapped in the epoxide form [83] in the reaction of adamantylideneadamantane with singlet oxygen affording dioxetane derivatives [84]. 

In sum, then, a good deal of experimental evidence has been gathered which supports, although indirectly, the intermediacy of a 1,4-biradical in the chemiluminescent reaction of simple dioxetanes. Yet there is no direct evidence that such biradicals exist with finite lifetimes. An attempted independent generation of a 1,4-biradical by decomposition of a dinitrite proved inconclusive (Suzuki, 1979). The influence of quenchers, radical scavengers, and external heavy atoms on the chemiluminescent reaction of trimethyldioxe-tane (Simo and Stauff, 1975) and adamantylideneadamantane-l,2-dioxetane [8] (Neidl and Stauff, 1978) was studied. While the authors interpret their results in terms of a relatively long-lived precursor to the excited-state product, namely the 1,4-biradical, the results are open to alternative explanations (Horn etal., 1978-79). 

N.B. Dioxygen can be implicated in reactions induced by anodic electron transfers. It is particularly the case in the oxidation of electron-rich double bonds in the presence of molecular oxygen. The reaction below exemplifies such a catalytic process (here in the case of adamantylideneadamantane) with the formation of dioxetane [149, 150]. Note that in this case the reaction is catalytic in electron (i.e. catalytic amount of charge extracted by the anode). 

Photooxygenation [2 + 2] is a unique method of preparing 1,2-endoperoxides, some of which can be relatively stable. For example, adamantylideneadamantane-l,2-dioxetane (520) was prepared by irradiation of biadamantylidene (521) in the presence of Methylene Blue and oxygen at 2irr>350nm in 66% chemical yield (Scheme 6.252).1436,1437... 

Cycloadditions.—Continuing interest has been shown in the photo-oxygenation of adamantylideneadamantane and in the reverse, thermally initiated, chemiluminescent fragmentation. Photo-oxygenation of the olefin affords the dioxetan (313) and the epoxide (312). With /ncso-tetraphenylporphin as sensitizer, (313) is the major product in all the solvents studied, whereas photo-oxygenation of the olefin in acetone and using a variety of dye sensitizers led to marked changes in the (312) (313) ratio. ... 

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