Cationic Cyclocodimerization. 4. Syntheses and Structures of Metacyclophane Derivatives. Cyclization Controlled by an Orbital Interaction and a Steric Constraint

Article abstract of DOI:10.1021/jo00384a005

Cationic cyclocodimerization of α,ω-bis(m-vinylphenyl)alkanes and 1-(m-vinylphenyl)-3-(p-vinylphenyl)propane with some comonomers were carried out.The reactions of α,ω-bis(m-vinylphenyl)alkanes gave metacyclophanes in 30-59percent yields.The structures of the metacyclophanes were determined by chemical shift differences between intraannular and extraannular protons, VT NMR spectroscopic measurements, and NOE experiments.Cyclocodimerizations of 1,3-bis(m-vinylphenyl)propane with several comonomers gave primarily two cyclophanes, although eight isomers are possible.Both 1,4-bis(m-vinylphenyl)butane and 1,5-bis(m-vinylphenyl)pentane cyclocodimerized with styrene to form exo,cis-1-methyl-3-styryl-anti-<3,n>metacyclophane as the major product.This selectivity is explained by molecular orbital calculation and examination of molecular models.The stabilities of intramolecularly face-to-face associated cations are discussed in relation to the reaction mechanism.