Investigation on Cl-F exchange mechanism occurring at C(sp2) and C(sp3) orbitals of halogenated cyclopentene

The mechanism of Cl-F exchange of halogenated cyclopentene with AlCl3 in dimethylformamide (DMF) or with AlCl4− in 1,1,1,3,3-pentachloropropane (HCC-240fa) was investigated. It was found that in DMF, AlCl3 preferred to attack the position with larger electron cloud density relatively like C(sp2) position, which was attributed to that AlCl3 was a strong Lewis acid, and in HCC-240fa, AlCl4− preferred to attack the position with smaller electron cloud density relatively like C(sp3) position, which was attributed to that AlCl4− was a Lewis base. Our experimental results showed that Cl-F exchange with AlCl3 occurred mainly on C(sp2) atom, and Cl-F exchange with AlCl4−occurred mainly on atom.