2- adamantane, photooxygenation

In fact, the chemiluminescence of an authenic sample of trans- 3,4-diphenyl-1,2-dioxetane, prepared by Kopecky s procedure [118] and then added to the DCA-sensitized reaction on traws-stilbene (E° = 1.51 V vs SCE), totally disappears within a few minutes [119]. In spite of this elegant demonstration, the intermediacy of these short-lived compounds required further direct evidence. In this regard, although different mechanistic pathways can account for the reaction products [34,120,121], Schaap et al. [98] isolated in the DCA-sensitized photooxygenations of adamantylidene-adamantane (E° = 1.46 V vs SCE) 21 and/or of several substituted 2,3-diphenyl-5,6-dihydro-l,4-dioxins (Eox in the range 0.72-1.07 V vs SCE) 22a-f the correspopnding stable 1,2-dioxetanes 23, 24a-f [Eqs. (10,11)] in good yields. 

Methoxymethylidene)adamantane (202) on photooxygenation in acetaldehyde, propanal and pivalaldehyde (RCHO) gives, apart from some adamantanone (203), the epimeric trioxanes (204) (Equation (29)) <85T208l>. The structures follow from the x-ray structure of the cw-epimer of (204) (R = Bu ). 

It is worth noting that only 1,2-dioxetanes (206) are obtained by photooxygenating 2-(phenoxymethylidene)adamantanes (205) in acetaldehyde as solvent (Equation (30)). However, these dioxetanes can be expanded to trioxanes at a later stage (see Section 6.20.6.4). Acyclic enol ethers behave in the same way. l,l-Di- -butyl-2-methoxyethylene (207), singlet oxygen and acetaldehyde cyclize to the cis and trans trioxanes (208) in 31% yield (Equation (31)). 

Photooxygenation of the ester alcohol 266 led to the allylic hydroperoxide 267 which could be converted into a series of 1,2,4-trioxane derivatives 268 (RVR = Adamantan, cyclo-Hex, cyclo-Pent, Me/Me and Et/FI) by BF3-catalyzed peroxyacetalization <2006LOC247> (Scbeme 79) the adamantane derivatives were characterized by X-ray diffraction and proved to be of moderate antimalarial activity. 

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