The kinetic profile of phthalazinium-2-dicyanomethanide 1,3-dipole with 2π-dipolarophiles: U-shaped dipolarophilic activity and classic type II dipole behaviour. Reaction rates and DFT calculations

Abstract

Kinetic data measured for the reactions of phthalazinium-2-dicyanomethanide 1,3-dipole with 26 dipolarophiles ranging from electron-poor to electron-rich place this dipole firmly in the class II category where reactions may be dipole-HOMO or -LUMO controlled depending on the nature of the dipolarophile. Minimal solvent polarity effects, small Hammett ρ values, and highly negative entropies of activation and DFT calculations support concerted non-synchronous cycloadditions and the observed regiochemistry for the full range of dipolarophiles.