Electrophilicity of aromatic triflones in σ-complexation processes

摘要: The kinetics of σ-complexation 2,6-bis(trifluoromethanesulfonyl)-4-nitroanisole (4) have been investigated over a large pH range 2–15.68 in methanol. Two competitive processes identified with the initial addition MeO− at unsubstituted 3-position 4 to give 1,3-dimethoxy adduct (4b-Me) and subsequent slow conversion this species into 1,1-dimethoxy isomer (4a-Me). Both 4a-Me 4b-Me are more stable than related adducts 2,6-dinitro-4-trifluromethanesulfonylanisole, i.e.5a-Me 5b-Me, 2,4,6-trinitroanisole, i.e.6a-Me 6b-Me, latter compound being conventional reference aromatic electrophile Meisenheimer complex chemistry. high thermodynamic stability (pKa = 10.48) 12.23) relative 5a-Me 10.68) 6a-Me 12.56) or 5b-Me 15.38) 6b-Me 16.46), is shown derive from an especially capacity para ortho SO2CF3group stabilize negative charge through Fπ-type polarization effects. From kinetic data, it appears that contribution methanol pathway formation much weaker found operate 1,1-complex experimental evidence suggesting reactivity 5 located just beyond region defining boundary between super- normal-electrophilicity Comparison our results available literature data show corresponds pKMeOHa value ∼ 10, agreement previous finding very effective solvent 1,3,5-tris(trifluoromethanesulfonyl)benzene (13; 9.12) Taking advantage observation pKH2Oa values for ring positions by nice linear correlation, approximate ranking electrophilicity triflones on E scale developed Mayr (Acc. Chem. Res. 2003, 36, 66) can be made.