Addition Reactions to syn- and anti-Sesquinorbornenes Involving Ionic Mechanisms. The Role of Tetracyanoethylene

Article abstract of DOI:10.1021/jo00185a006

Addition of bromine or of acids to anti-sesquinorbornene is more rapid and less readily reversible than that to the syn isomer, whereas other addition reactions proceeding by concerted or free-radical mechanisms show a small rate advantage for syn-sesquinorbornene and no reversibility.Tetracyanoethylene (TCNE) does not undergo cycloaddition with syn- or anti-sesquinorbornene, nor can any dipolar ion from TCNE and sesquinorbornene be trapped by methanol, as in the case of TCNE and vinyl ethers.However, under the conditions of such experiments TCNE catalyzes the addition of methanol to yield sesquinorbornyl methyl ether, or of water to yield sesquinorbornanol, the TCNE undergoing no apparent chemical change.From a comparative study of TCNE and p-toluenesulfonic acid it is concluded that the TCNE reaction is an example of acid catalysis, probably by the complex between TCNE and the alcohol or water. syn-Sesquinorbornene adds methanol in CD3CN with the lower equilibrium constant of about 0.54 +/- 0.05 L/mol at ca. 30 deg C. anti-Sesquinorbornene in similar additions shows an equilibrium more favorable to addition by about 3 orders of magnitude.These reactions are discussed in light of the general character and behavior of the sesquinorbornenes.A new route to anti-sesquinorbornene is described that gives better yields than the former electrolytic preparation.