Rearrangements in the cycloaddition of tetracyanoethylene to 3-methylenecyclohexa-1,4-dienes and homofulvenes
Abstract
Reaction of tetracyanoethylene with 6,6-disubstituted derivatives of 3-methylenecyclohexa-1,4-diene gives rise to four classes of adduct: spiro[3,5]nona-5,8-dienes, bicyclo[4,3,0]nona-1,4-dienes, bicyclo[4,3,0]nona-1,3-dienes, and tetracyanopropylbenzene derivatives. The relative proportions of these depend both on the detailed structure of the triene and on the solvent. Both these results and the stereochemistry of the bicyclononadiene adducts are discussed in terms of an ionic mechanism in which the lifetime of the initially formed zwitterion is important. The structures of products from tetracyanoethylene and 2-methylenebicyclo[3,1,0]hex-3-ene derivatives are also consistent with an ionic addition mechanism.