· Allyl Trifluoromethanesulfonate
· (MW 191.16)
(extremely reactive allylating agent;1,2 attacks a variety of S-, P-, N-, or O-containing molecules;2 ring expansion reaction3)
Alternate Name: allyl triflate.
Physical Data: d 1.47 g cm-3.
Solubility: sol chlorinated hydrocarbons.
Form Supplied in: colorless liquid.
Analysis of Reagent Purity: IR (neat, cm-1) 2970 (w), 1413 (m), 1281 (s), 1248 (s), 1194 (s), 1149 (m), 913 (m); 1H NMR (CCl4, ppm) d 6.03 (m, 1H), 5.43 (m, 2H), 4.92 (m, 2H); 19F NMR (ppm) j 74.5 (s).
Preparative Methods: allyl triflate is prepared by the reaction of Trifluoromethanesulfonic Anhydride (1 equiv) and allyl alcohol (1 equiv) in the presence of pyridine (1 equiv) in carbon tetrachloride at 0 °C.1 The insoluble pyridine salt is removed by filtration through sodium sulfate, and the resulting solution is used directly for allylation reactions. The yield of the reaction is reported to be 75 ± 5% based on quantitative NMR analysis of aliquots.
Purification: a pure sample may be obtained by distillation (safety shield).2 The product must be trapped in a cold receiver (-78 °C).
Handling, Storage, and Precautions: allyl triflate must be stored at -78 °C in a vented flask. The half-life of the neat reagent is ~10 min at room temperature, and the reagent in carbon tetrachloride solution completely decomposed in 3 days at room temperature. Allyl triflate reacts violently with nitrogen, or oxygen-containing solvents such as DMSO, DMF, or acetonitrile. The reagent is an extremely reactive allylating agent, and contact or inhalation should be avoided. Use in a fume hood.
Allyl triflate is an extremely reactive allylating agent and reacts readily with 2-vinylthiapentane (1). a-Vinyl-S-allylsulfonium salt (2) thus obtained undergoes a 2,3-sigmatropic rearrangement upon treatment with a base (1,8-Diazabicyclo[5.4.0]undec-7-ene) (eq 1). Two rearrangement products (3) and (4) were obtained in the ratio of 1:1 that were derived from endocyclic and exocyclic ylides, respectively. Repeated application of this sequence to the eight-membered ring sulfide (4) produced medium- and large-sized ring sulfides. No products derived from the endocyclic ylides were observed in the ring expansion sequence from cyclic sulfide (4). 2-Vinylthiane also undergoes allylation and a 2,3-sigmatropic rearrangement sequence to produce a 1:2 mixture of cyclic sulfides
(7) and (8) (eq 2). An improved ratio of products (7:8 = 1:24) was obtained by using Lithium Diisopropylamide at -70 °C for ylide generation, and forcing the rearrangement to occur rapidly under dilute conditions (eq 3). The 2,3-sigmatropic rearrangement of six-membered rings takes place with remarkable stereospecificity,4 and only the trans isomer of nine-membered ring sulfide (8) was observed.
C-, N-, O-Allylation.
5-Chloromercuriuridine (9) undergoes a palladium-catalyzed C-allylation reaction with allyl triflate (eq 4).5 Transmetalation of 5-chloromercuriuridine (9) and Palladium(II) Chloride generates the organopalladium(II) complex (10), which then reacts with allyl triflate to produce C-5 allyl-substituted uridine (11) in 52% yield. N-Allylation of O-trimethylsilyloxime (12) with allyl triflate is a convenient method for nitrone synthesis (eq 5).6 The initial allylation produces the (E)-nitrone, which then isomerizes to the more stable (Z)-isomer. Allyl triflate reacts with alcohols to give O-allylation products. Alcohols of low nucleophilicity which contain electron-withdrawing substituents such as
2,2-dinitropropanol, 2,2,2-trinitroethanol, and 2,2-dinitro-1,3-propanediol even react with allyl triflate to produce the corresponding allyl ethers in 53%, 33%, and 28% yield, respectively.1 These etherification reactions were carried out at room temperature in the presence of Na2SO4 as a heterogeneous acid scavenger.
- 1. Beard, C. D.; Baum, K.; Grakauskas, V. JOC 1973, 38, 3673.
- 2. Vedejs, E.; Engler, D. A.; Mullins, M. J. JOC 1977, 42, 3109.
- 3. (a) Vedejs, E.; Mullins, M. J.; Renga, J. M.; Singer, S. P. TL 1978, 519. (b) See also Schmid, R.; Schmid, H. HCA 1977, 60, 1361. (c) Vedejs, E.; Hagen, J. P. JACS 1975, 97, 6878. (d) Vedejs, E.; Singer, S. P. JOC 1978, 43, 4884.
- 4. Vedejs, E.; Arco, M. J.; Renga, J. M. TL 1978, 523.
- 5. Hassan, M. E. CJC 1991, 69, 198.
- 6. LeBel, N. A.; Balasubramanian, N. TL 1985, 26, 4331.
Myong Ji University, Seoul, Korea
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