Electrocyclic reactions Cope rearrangement

A domino process based on the twofold addition of alkenyl anions to a squarate ester was used by Paquette and coworkers [96] for the total synthesis of the triqui-nane sesquiterpene hypnophilin (4-284). The three-component reaction of 4-281,4-282 and vinyl lithium gave primarily the trans- and cis-adducts A and B, which furnished D either by an electrocyclic ring opening/ring closure via C or a dianionic oxy-Cope rearrangement (Scheme 4.60). Further transformations led to E and F, which resulted in the formation of 4-283 on treatment with acid. 

The Cope rearrangement mechanism can be also strongly affected by other substituents. Thus, the normal electrocyclic process in the thermal isomerization of divinyl aromatics has been suppressed relative to the thermolysis of l,2-bis(trifluorovinyl)naphthalene 438 (in benzene, at 193 °C, 24 h)231. Three major products 440-442 were isolated from the reaction mixture, but none of them was the expected product 439. Also formed in low... 

Indeed, c -l,2-divinylcyclopropanes give this rearrangement so rapidly that they generally cannot be isolated at room temperature,458 though exceptions are known.459 When heated, 1,5-diynes are converted to 3,4-dimethylenecyclobutenes.460 A rate-determining Cope rearrangement is followed by a very rapid electrocyclic (8-29) reaction. The interconversion of... 

A significant acceleration of the electrocyclic ring opening of benzocyclobutene derivatives has been disclosed under the influence of a -silicon atom.55 This effect has been associated with the adjacent anion-driven electrocyclic reactions such as oxy-Cope rearrangement. 

Radical cations derived from a variety of hexadiene systems constitute an interesting family of intermediates, since they are related to the potential mechanistic extremes of the Cope rearrangement. The electrocyclic reaction of a hexadiene radical cation has three mechanistic extremes a) addition precedes cleavage (associative mechanism) b) cleavage preceeds addition (dissociative mechanism) c) addition and cleavage occur in coordinated fashion (concerted mechanism). To date, radical cations corresponding to all three mechanistic extremes have been characterized. This illustrates remarkable differences between... 

The electrocyclic reaction is very similar to the Claisen rearrangement of CoPe rearrangement... 

Cope rearrangement, ing. Electrocyclic reactions can occur by either conrotatory or disrota-1251 tory paths, depending on the symmetry of the terminal lobes of the n... 

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