Methyl pentafluorophenyl carbonate

In 1998, Ube Industries, Ltd. discovered that pentafluorobenzoates, such as methyl pentafluorobenzoate (62), can be used as additives in small quantities [92], Also, in 1999, Toyota Central R D Labs found that fluorinated benzoates, such as methyl 2,6-difluorobenzoate (63), can be used as additives in small quantities [93], and in 2002, Ube Industries, Ltd. found that pentafluorophenol compounds, such as pentafluorophenyl methanesulfonate (64) and methyl pentafluorophenyl carbonate (65), can be used as additives in small quantities [94]. 

Bis(pentafluorophenyl) sulfite added to a soln. of N-r rFbutyloxycarbonylglycine in DMF containing 1 eq. pyridine, and stirred for 0.1-1 h at 20° - product. Y 96% (70% from pentafluorophenol with DCCI as condensing agent). There was no racemization with a-subst. derivs. F.e.s. A.V. Hina et al., Izv. Akad. Nauk SSSR Ser. Khim. 1988, 2816-8 with methyl pentafluorophenyl carbonate cf. Izv. Akad. Nauk LatvSSR Ser. Khim. 1988, 624. 

These results clearly show that the potential energy surface can contain a series of minima. The fact that selectivity in re-attack by the F ions can be observed indicates that the differences between the energy barriers for the secondary reactions control the distribution of the final products. The multistep character of these processes is further illustrated by the reactions observed when enolate anions are used as reactant ions. The ambident enolate anions may react with methyl pentafluorophenyl ether at the carbon or the oxygen site. If they react with the carbon site at the fluorine-bearing carbon atoms, then the molecule in the F ion/molecule complex formed contains relatively acidic hydrogen atoms so that proton transfer to the displaced F ion may occur. An example is given in (47) where the enolate anion, generated by HF loss, is not observed. An intramolecular nucleophilic aromatic substitution occurs instead and leads to a second F ion/ molecule complex. The F" ion in this complex then re-attacks the substituted benzofuran molecule formed, either by proton transfer or SN2 substitution. 

---