Tetracyclone function

Conjugated diynes can function as dienophiles in Diels-Alder reactions, and adducts have been obtained in which one or both of the triple bonds participates. Most of the studies have involved the use of substituted cyclopentadienones, e.g. tetraphenylcyclopentadienone ( tetracyclone ), which form adducts that undergo decarbonylation to give aromatic hydrocarbons. Butadiyne itself reacts with tetracyclone to give hexaphenylquaterphenyl (221) while diphenylbutadiyne gives the mono(222)- and di(223)-adduct . Bis(4-biphenylyl)butadiyne gives the monoadduct 224 . 

Substrates with electron acceptors are given in Scheme 4. For these rather unreactive n-systems, besides longer reaction times and excess dioxirane, elevated temperature (ca. 25 °C) was essential for complete conversion into their corresponding epoxides. Fortunately, these epoxides, which were all obtained quantitatively, were sufficiently stable for rigorous characterization. The specific substrate types include oc,P-unsaturated acids [20] 21 and esters [20] 22 hydroxychalcones [21] 23 a,P-enones [20] 24 2-cyclohexenones [20] 25 methylene-P-lactones [22] 26 tetracyclone [20] 27 and naphthaquinone [16] 28. The particular advantage of the dioxirane methodology is that labile functional groups, e.g. the phenolic moiety in the chalcones, do not require protection. 

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