Alkyl 2,2,2-Trifluoroethanesulfonates (Tresylates): Elimination-Addition vs Bimolecular Nucleophilic Substitution in Reactions with Nucleophiles in Aqueous Media(1).
Alkyl 2,2,2-trifluoroethanesulfonate esters (tresylates), ROSO(2)CH(2)CF(3), react with aqueous base (pH >/= 9) to give the (alkoxysulfonyl)acetic acid, ROSO(2)CH(2)COOH; with the further addition of either a primary or secondary amine or of an alkanethiol, the product is the either the corresponding amide, ROSO(2)CH(2)C(O)NR(1)R(2), or a mixture in which the ketene dithioacetal, ROSO(2)CH=C(SR(1))(2), or the thioorthoester, ROSO(2)CH(2)C(SR(1))(3), may predominate. Kinetic and product studies are consistent with the following: (a) the reaction of tresylates with water is the normal sulfonic ester hydrolysis and (b) reaction with hydroxide is an (E1cB)(rev) process with loss of HF to yield the alkyl 2,2-difluoroethenesulfonate, ROSO(2)CH=CF(2), which rapidly yields the observed products. Benzyl 2,2,2-trifluoroethyl sulfone reacts analogously. The relationship between these observation with small molecules and those of earlier workers with tresyl agarose is discussed.
King
James F.
JF
Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7.
Gill
Manjinder S.
MS