The solvolysis of 3-cyclooctatetraenylpropyl and 4-cyclooctatetraenylbutyl p-nitrobenzenesulfonates in 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol

Abstract

The advantage of the use, compared to acetic acid, of 2,2,2- trifluoroethanol and 1,1,1,3,3,3-hexa-fluoropropan-2-ol for promoting π-participation in the solvolytic reactions of 3-cyclooctatetraenyl- propyl and 4-cyclooctatetraenylbutyl p-nitrobenzenesulfonates is demonstrated.    

3-Cyclooctatetraenylpropyl p-nitrobenzenesulfonate solvolyses in buffered trifluoroethanol and hexafluoropropan-2-ol with π- participation occurring to the extent of 73 and 99.5 %, respectively. The sole cyclized product is 2,9a-dihydro-1H-cyclopentacyclooctene.

4-Cyclooctatetraenylbutyl p-nitrobenzenesulfonate solvolyses in buffered trifluoroethanol and hexafluoropropan-2-ol with π- participation occurring to the extent of 94 and 100%, respectively. In buffered trifluoroethanol, the major cyclized products are the two isomers of 10a-(2',2',2'-tri-fluoroethoxy)-1,2,3,4,4a,10a- hexahydrobenzocyclooctene (61.7%) and 1,2,3,10a-tetrahydrobenzo- cyclooctene (28.9%). The tetraene is almost the exclusive product (98.8%) in buffered hexafluoro-propan-2-ol.    

The probable involvement of substituted homotropylium ions and the role of ion-pairs in the solvolyses are discussed.