Migrating ring

These transformations generally involve several steps catalyzed by antimony(V) fluoride, including double-bond migration, ring closure, and finally double-bond migration in the initially formed cyclic intermediate so as to arrive at the more stable perfluoro(1,2-dialkylcycloalkene). The mechanism of these reactions has been discussed.21... 

Bis-(trifluoromethyl)-phenyl plays the role of migrating ring in the Smiles rearrangement in the Najera and co-workers [106,107] modification of the olefination reaction. Judka and Makosza (Judka and Makosza, 2006, personal commimication) have shown that pentachlorophenyl and some very simple phenyl derivatives may be conveniently used in the olefination reactions imder mild conditions. Indubitably, several other aromatic and hete-rocycHc systems will be estabhshed as the templates in the direct olefination reaction, allowing for convenient choice of experimental conditions and stereochemical bias. 

Studies by Juba and by Kocienski have shown that the nature of the suhbne may exert a decisive effect on the efficiency of the olefination reaction. Diversification of the migrating rings in the Smiles rearrangement could be benefactions for extending the scope of appHcation of the reaction. 

Aissa reported [109] that a combination of ferf-butyltetrazolyl as the migrating ring and cesium carbonate as the base in THF-DMF, at reflux fem-perafure, enables cyclizafion reacfions. As indicafed in Scheme 117, a six-membered ring was formed in an excellent yield. Cyclization of 347 pro-... 

The first step of the reaction is the formation of the nucleophile by deprotonation. The substrate then has to adopt the reactive conformation in which the plane of the migrating ring is perpendicular to the Z-Z bond. The nucleophile attacks the ring in an Ipso fashion to form a five-membered transition state that affords the product. 

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