Synthesis of some novel trifluoromethanesulfonates and their reactions with alcohols

Abstract

Allyl triflate, propargyl triflate, pentyl triflate, 2-(2-fluoro-2,2-dinitroethoxy)ethyl triflate, 2-fluoro-2,2-dinitroethyl triflate, and 1,2,3-propanetritriflate were prepared from the alcohols using triflic anhydride and pyridine. 1,4-Butaneditriflate was formed from tetrahydrofuran and triflic anhydride. In the presence of potassium carbonate, pentyl triflate, allyl triflate, propargyl triflate, 1,4-butaneditriflate, and 2-( 2-fluoro-2-2-dinitroethyoxy)ethyl triflate reacted in chlorinated hydrocarbon solvents at ambient temperature with 2-fluoro-2,2dinitroethanol to give the corresponding ethers, without skeletal rearrangement. l12,3-Propanetritriflate underwent monosubstitution and elimination to yield 3-( 2-fluoro-2,2-dinitroethoxy)-2-propenyl triflate. Pentyl triflate and 2,2,2-trifluoroethanol gave pentyl 2,2,2-trifluoroethyl ether. When sodium sulfate was used instead of potassium carbonate to scavenge liberated triflic acid, pentyl triflate and 2,2-dinitropropanol gave a mixture of the 1-, 2-, and 3-pentyl ethers. Under these conditions, 2-fluoro-2,2-dinitroethanol, 2,2-dinitropropanol, and 2,2,2-trinitroethanol, as well as pentanol, reacted with isopropyl triflate to give the corresponding isopropyl ethers. Allyl triflate was allowed to react similarly with 2,2-dinitropropanol, 2,2,2-trinitroethanol, and 2,2-dinitro-1,3propanediol to give the allyl ethers. The high reactivity of the trifluoromethanesulfonate (triflate) group in solvolysis and displacement reactions has been the subject of a number of recent investigations. Thus, methyl and ethyl triflates were reported to undergo solvolysis more than lo4 times as fast as the corresponding tosylate~.~~~ The use of the triflate leaving group in otherwise unreactive polycyclic systems has extended the range of solvolysis reaction^,^-^ and vinyl triflates have been used extensively in studies of vinyl ~ations.~-~O Xo attempts have been reported, however, to prepare a triflate ester more reactive than the ethyl derivative. Such extremely reactive alkylating agents would be expected to extend the range of weakly nucleophilic reagents that can be alkylated. The triflates prepared in this work are shown in Table I. Most of these compounds were synthesized from the corresponding alcohols by the commonly used4 triflic anhydride-pyridine method. Methylene chloride and carbon tetrachloride were used as solvents. Methyl triflate, because of its low boiling point, was prepared conveniently, from dimethyl sulfate by a procedure previously used for the corresponding fluorosulfonate.'l The reaction of tetrahydrofuran with triflic anhydride gave 1,4-butaneditriflate1 a reaction similar to ring openings with mixed sulfonic-carboxylic anhydrides. l2 This ditriflate and l12,3-propanetriflate, prepared from glycerol, are the first reported polyfunctional examples. Allyl triflate, propargyl triflate, and isopropyl triflate were not sufficiently stable for elemental analysis and were characterized by spectral data, described in