Solvolysis of 1-aryl-2,2,2-trifluoroethyl sulfonates. Kinetic and stereochemical effects in the generation of highly electron-deficient carbocations

Abstract

Solvolysis rates of sulfonates XC6H4CH(03SR)CF3 (R = p-Tol or CF3) correlate with +( ) with values of p+ between -6.7 and -11.9 depending upon solvent. For the tosylates the rates depend on the solvent parameter F0Ts with values of Wqts of 0.76 (X = p-MeO), 0.94 (X = p-Me), and 0.69 (X = H). These results are interpreted in terms of rate-limiting carbocation formation (the kc process). Rates for PhCH(OTf)CF3 (12e) in ten solvents gave a scattered correlation with F0Ts> and optically active 12e reacted with racemization in TFÁ and HFIP and significant inversion in EtOH and AcOH.These results indicate that nucleophilic solvent participation becomes important with this derivative in the more nucleophilic solvents. Deuterium isotope effects for PhCD(OTf)CF3 are not a definitive criterion of mechanism but are consistent with this interpretation.The reactivity of 1 -aryl-1 -methyl-2,2,2-trifluoroethyl tosylates (I) has been investigated by ourselves1 and by (1) (a)

Dynamics for reactions of ion pairs in aqueous solution: reactivity of tosylate anion ion paired with the highly destabilized 1‐(4‐methylphenyl)‐2,2,2‐trifluoroethyl carbocation

“…1-(4-Methylphenyl)-2,2,2-trifluoroethanol ( 4-OH ) was synthesized by reduction of the ketone with sodium borohydride. [18] The crude alcohol was purified by silica-gel column chromatography eluting with n-hexane: yield 78 %. 1 H NMR (400 MHz, CDCl 3 ): δ 7.36 (AB, 2H, J = 8.0 Hz, Ar H ), 7.22 (AB, 2H, J = 8.0 Hz, Ar H ), 4.98 (dq, 1H, J = 4.4 Hz, 2 J = 6.4 Hz, C H CF 3 ), 2.60 (d, 1H, J = 4.4 Hz, CHO H ), 2.37 (s, 3H, C H 3 ).…”

“…[9,11] We now extend this work and report the results of a study of the reorganization of the ion pair intermediate 4 + • − OSO 2 C 6 H 4 -4-Me of solvolysis of a ring-substituted 1-phenyl-2,2,2-trifluoroethyl tosylate, where the carbocation is destabilized by the strongly electron-withdrawing α-CF 3 substituent. [12–16] This work was initiated for the following reasons.…”

“…[5,6] By comparison, carbocation-anion pairs to the much more unstable 1-(4-methylphenyl)-2,2,2-trifluorethyl carbocation can only be generated using a more weakly basic leaving group anion, such as tosylate anion. [12,14,15] There is little or no data for addition of tosylate anion to carbocations in aqueous solution, so that it is not clear whether addition of this weakly basic anion competes effectively with addition of the relatively nucleophilic solvent water. We were therefore interested in determining whether the ion pair intermediate of the reaction of 1-(4-methylphenyl)-2,2,2-trifluorethyl tosylate would undergo internal return of the weakly nucleophilic sulfonate anion in the nucleophilic solvent water.…”

Preparation of symmetrical and unsymmetrical monomers towards bridge trifluoromethylated poly(p-phenylenevinylene)

“…Indeed, the strong electron withdrawing trifluoromethyl group (s þ p 0.61) [19] has been shown to retard solvolysis of benzylic tosylates by over six orders of magnitude [20], and thus our mono-trifluoromethylated compounds are ideal systems for generating monomers with an unsymmetrical arrangement of leaving group and polarizer in both high selectivity and high yield. Common drawbacks of unsymmetrical monomer formation are problems with over-substitution, use of excess substrate, tedious separations and recuperation of expensive starting materials [21].…”

“…The literature reports of the solvolysis and other substitutions reactions of trifluoromethyl bearing benzylic tosylates [20,22], mesylates and triflates [23] led us to examine the preparation and substitution potential of some alternative superior leaving groups Scheme 5.…”