Frontier-Controlled Cycloaddition Reactions of Phencyclone with Electron-Rich Dienophiles via Charge-Transfer Complexes: Kinetic Study and Its Mechanistic Aspects

Article abstract of DOI:10.1021/jo00332a015

Quantitative spectroscopic evidence indicates that phencyclone (2-oxo-1,3-diphenyl-2H-cyclopentaphenanthrene, 1a) forms a charge-transfer complex with dienophiles involving medium-membered-ring unsaturated compounds.Analysis of the second-order rate constants for the cycloaddition in 1a with the dienophiles shows that there is a decrease in the apparent rate constants with increased concentration of the dienophiles.These data can be interpreted as evidence for the presence of a charge-transfer complex in the reaction mixture.It appears likely that the cycloaddition of 1a with good donor molecules proceeds via charge-transfer complexes, and the charge-transfer complexation plays an important role in determining both the regiochemistry and the stereochemistry of the adducts.