Cyclobutadiene, generation in situ

Cyclization, solvolytic, 54, 84 Cycloalkene oxides, 1-methyl, conversion to exocyclic methylene alcohols, 53, 20 Cyclobutadiene, generation in situ, 50, 23... 

The reaction of o-diphenylcyclobutadiene (generated in situ by oxidation of its iron tricarbonyl complex) with p-benzoquinone yields A as the exclusive product. With tetracyanoethylene, however, B and C are formed in a 1 7 ratio. Discuss these results, and explain how they relate to the question of the square versus rectangular shape of cyclobutadiene. 

Cyclobutadiene is one of the most attractive molecules. A conceptually new and simple method using intramolecular coupling of l-metallo-4-halobutadiene was reported to form cyclobutadiene derivatives by Takahashi and coworkers (Eq. 34). l-Zircona-4-halobutadiene derivatives, generated in situ by treatment of zirconacyclopentadienes with one equivalent of iodine, react in the presence... 

The complex exhibits remarkable stabiUty, and the cyclobutadiene undergoes reactions without destmction of the ring (139). Cyclobutadieneiron tricarbonyl [12078-17-0] can be oxidized to generate cyclobutadiene in situ (140). 

Cyclobutadieneiron tricarbonyl may also be produced through reaction of 3,4-dichlorocyclobutene with Na2Fe(CO)4,5 and by irradiation of a-pyrone followed by treatment with Fe2(CO)9 . The method outlined here is the most convenient procedure especially when considerable quantities (10 g. or more) of cyclobutadieneiron tricarbonyl are required. The analogous reaction of derivatives of 3,4-dihalocyclobutenes with Fe2(CO)9 affords the corresponding cyclobutadieneiron tricarbonyl complexes. Cyclobutadieneiron tricarbonyl can be oxidized to generate cyclobutadiene in situ.7... 

Several exhaustive reviews have dealt with synthetic and theoretical aspects of the cyclobutadiene problem9. The usual routes for the in situ generation of cyclobuta-... 

Another example of an in situ generated 1,4-dipol is the reaction of 2,4-bis(diethyl-amino)cyclobutadiene 211 with diphenylcarbodiimide which affords the pyridine derivative 212184,... 

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