Cycloaddition Cyclohexane-1,4-dione

Within the cubane synthesis the initially produced cyclobutadiene moiety (see p. 329) is only stable as an iron(O) complex (M. Avram, 1964 G.F. Emerson, 1965 M.P. Cava, 1967). When this complex is destroyed by oxidation with cerium(lV) in the presence of a dienophilic quinone derivative, the cycloaddition takes place immediately. Irradiation leads to a further cyclobutane ring closure. The cubane synthesis also exemplifies another general approach to cyclobutane derivatives. This starts with cyclopentanone or cyclohexane-dione derivatives which are brominated and treated with strong base. A Favorskii rearrangement then leads to ring contraction (J.C. Barborak, 1966). 

Dipolar cycloadditkm reactions of nitrones to olefins, 46, 1,3-Dipolar cycloadditions with 3-phenylsydnone, 45, 98 Dispiro[5 1 5 l]tetradecane-7,14-dione, photolysis to cyclohexylidene-cyclohexane, 47, 34 preparation from cyclohexanecarbonyl chlonde and triethylamine, 47,34 Displacement of bromine from 1-bromo-2-fluoroheptane to give 2-fluoro-heptyl acetate, 46, 37... 

Conjugate addition, 34-5, 51-2,53, 132, 133 Conjugate hydroxymethylation, 59-60 Copper(n) bromide, 54 Copper([) chloride, 120 Copper(n) chloride, 120 Copper(i) cyanide, 7,52, 53 Copper(i) iodide, 54 Corey s internal quench, 104 Cyanohydrin trimethylsilyl ether, 137 Cycloaddition. 34,112 Cydobutane-l,2-dione, 135 Cyclohept-2-dione, 135 Cyclohex-2-enone, 52,123 Cyclohcxa-1,3-diene, 26 Cyclohexane carboxaldehyde, 22-3,69 73,78... 

Carbonyl diisocyanate (46) was shown to undergo a Diels-Alder type of cycloaddition with azomethines to give 2,3,6,7-tetrahydro-4/7,8/7-[l,3,5]triazino[2,l-Z>][l,3,5]oxadiazin-4,8-diones (16) (Scheme 5). A large variety of the triazino[2,l-ft][l,3,5]oxadiazines were realized by the suitable selection of dienophiles. Thus, l,3,5-triazino[2,l-Z>][l,3,5]oxadiazines (17), (18 R = NMe), and (19) and were synthesized by the reaction of carbonyl diisocyanate with alkyl or aryl isocyanates, dimethyl cyanamide, or aliphatic carbodiimides, respectively <86CB1133>. Due to the high reactivity of the cumulated double bonds, carbonyl diisocyanate (46) was also found to undergo [4 + 2] cycloadditions with cyclohexanone to yield cyclohexan-l-spiro-9 -[l,3,5]-oxadiazino-[3,4-e][l,3,5j-dioxazin-5 -spiro-l"-cyclohexane-2, 7 -dione (47) (Scheme 6) <76LA1634>. 

A few examples of 2-spiroindoline 2f/-chromenes were reported from the condensation of l,3,3-trimethyl-2-methyleneindoline with salicylalde-hydes, under microwave irradiation in solvent-free conditions (14H(89)1017). [3 + 3] Cycloaddition reactions of a,p-unsaturated aldehydes with cyclohexane-1,3-dione or 4-pyran-3,6-dione mediated by a zeolitic imidazolate framework nanosphere gave access to 2,2-disubstituted tetrahydro- or hexahydro-2f/-chromenes, respectively (14JA13963). 

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