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Cyclobutenediones cycloaddition reactions

Annulation of heterocycles with a cyclobutene ring has been achieved by photochemical (2 + 2)-cycloaddition with acetylenes. Both maleic anhydride and N-substituted maleimides yielded 3-oxa- or 3-aza-bicyclo[3.2.0l-hept-6-ene-2,4-diones (167).,89,9° Vinylene carbonates also entered into a cycloaddition reaction with acetylenes to afford 168, which has been employed as starting material for the synthesis of cyclo-butadiene(tricarbonyl)iron or cyclobutenedione.19,-193 3,4-Dihydro-2/f-pyran and 5-methyl-2,3-dihydrofuran reacted with diphenylacetylene to... [Pg.294]

Apart from these methods based on the squaric acid family, direct formation of cyclobutenedione rings by [4 + 2] and [2 -i- 2] cycloaddition reactions is a plausible approach to variably substituted 4-hydroxy-2-cyclobutenone systems [47-54]. [Pg.5]

The reaction of iron-carbonyl complexes with alkynes led to cyclobutenediones, which is formally a [2 + 1 + 1]-cycloaddition process for the formation of a cyclobutene derivative (Scheme 9.22) [49]. Nevertheless, in this reaction the liberation of the ligand is initiated by addition of stoichiometric amounts of copper] 11) salts and the use of various alkynes leads to interesting products such as 30 in good yields. [Pg.255]

A formal [2+1+1] cycloaddition is achieved by reaction of alkynes with an iron carbonyl species that is prepared in situ from dodecacarbonyltriiron Fe3(CO)i2 in the presence of certain amines. This procedure provides cyclobutenediones in moderate to good yields after demetalation with copper(II) chloride (Scheme 4-14). Instead of amines and dodecacarbonyltriiron, alkoxides such as ter/-BuOK can be reacted with pentacarbonyliron to give reactive carbonyliron intermediates that undergo cyclization... [Pg.563]


See other pages where Cyclobutenediones cycloaddition reactions is mentioned: [Pg.57]    [Pg.57]    [Pg.85]    [Pg.390]    [Pg.261]    [Pg.1130]    [Pg.95]    [Pg.1130]    [Pg.5263]    [Pg.261]    [Pg.26]   


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Cyclobutenediones

Cyclobutenediones, reactions

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