Solvolysis of 1‐p‐Methoxyphenyl‐2‐Methylpropen‐1‐Yl Trifluoroacetate and 3,5‐Dinitrobenzoate

Abstract

The reactions of l-p-methoxyphenyl-2-methylpropen-I-yl trifluoroacetate (I-OCOCF,) and 3,5-<1initrobenzoate (I-OONB) in AcOH/NaOAc or with amines in 2,2,2-trifluoroethanol (TFE) were investigated. In TFE, I-OONB gives trifluoroethyl 3,5-<1initrobenzoate (II) and the ketone AnCOCHMe, (III) in a second order reaction with five amines and with CF, CH, ONa, and I-OCOCF, gives a second order reaction with 2,6-lutidine. In AcOH/NaOAc, I-OCOCF, gives the corresponding acetate I-OAc, and I-OONB gives I-OAc and III. The kAcOH/k AcOO values are 5.5 -6.2 for I -OCOCF, and 1.03 ± 0.05 for I-OONB. It is suggested that the rate determining step in TFE is the attack of CF ,CH,O-(formed from the amine and TFE) on the carbonyl of the ester group in a BAC2 mechanism. In AcOH, an electrophilic addition-elimination mechanism (AdE-E) for the reaction of I -OCOCF, is supported by the solvent isotope effect. The solvent isotope effect and the products from I-OONB in AcOH are consistent with an SN 1 mechanism, but since the kCl/kOONB ratio is lower than that in saturated systems, an AAC2 mechanism cannot be unequivocally excluded. The effect of the leaving group in the vinylic SN I reaction is discussed.Many mechanistic routes are available for nucleophilic vinylic substitution [I), and we previously showed that the vinylic SN1 mechanism [2] operates for many a-arylvinyl substrates [3]. Gal had shown [4][5][6] that competition of this route with electrophilic addition-elimination (Ad E -E) [7] and with nucleophilic additionelimination (Ad N -E) [I] is important for several systems, and competition with the E2 mechanism was also observed [8].With a-activated substituted vinyl sulphonate esters such as trifluoromethanesulphonates (triflates) [9]