Triflic anhydride reaction with alcohols

Reaction with Alcohols and Phenols. The reaction of alcohols and phenols with triflic anhydride (Tf20) at 0°C in the presence of a base (usually Pyridine) in an inert solvent (usually dichloromethane) for 2-24 h affords the corresponding reactive trifluoromethanesulfonate esters (triflates). When triflic anhydride and pyridine are combined, the pyridinium salt forms immediately and normally precipitates out from the reaction mixture. Nevertheless, the salt is an effective esterifying agent, reacting with the added alcohol to give triflates in high yields (eq 1). ... 

Reaction with Alcohols and Phenols. Reaction of alcohols with triflic anhydride in the presence of a base affords the corresponding alkyl triflate, a versatile intermediate that can be used to generate an allylic carbocation in a [4+3] cycloaddition (91). ... 

Reaction with Alcohols and Phenols. The reaction of alcohols and phenols with triflic anhydride (TfzO) at 0°C in the... 

The chloride of triflic acid (trifluoromethanesulfonyl chloride) is an effective sulfonylating agent Like triflic anhydride, it usually reacts with alcohols and other nucleophiles with the formation of the corresponding derivatives of tnflic acid [69] However, in some reactions, it acts as a chlorinating reagent [98] The reactions of tnfluoromethanesulfonyl chloride with 1,3-dicarbonyl compounds or some carboxylic esters in the presence of a base result m the formation of chlonnated products in high yields (equation 49)... 

Treatment of the alcohol ( ) with trifluoromethylsulfonic anhydride (triflic anhydride) at -78 C afforded the ester (1 ) which could be isolated and characterized. We knew from previous experience (2J that sulfonyl esters vicinal to an isopropylidene acetal are relatively stable. The triflate T,) reacted cleanly with potassium azide and 18-crown-6 in dichloromethane at room temperature. The crystalline product [68% overall from (1 )] was not the azide ( ) but the isomeric A -triazoline ( )- Clearly the initially formed azide (18) had undergone intramolecular 1,3-cyclo-addition to the double bond of the unsaturated ester (21- ). The stereochemistry of the triazoline (1 ), determined by proton nmr spectroscopy, showed that the reaction was stereospecific. There are several known examples of this reaction ( ), including one in the carbohydrate series ( ). When the triazoline was treated with sodium ethoxide ( ) the diazoester ( ) was rapidly formed by ring-opening and was isolated in 85% yield, Hydrogenolysis of the diazo group of (M) gave the required pyrrolidine ester ( ) (90%). 

Glycosylation of phenols and even hindered alcohols is possible by reaction with an O-protected 1-phenylsulfinylglucose (1, excess) and triflic anhydride at -78° (equation I).2 The a/p ratio is influenced by the protective groups and the solvent. Use of CH2C12 or propionitrile favors p-glycosylation, whereas toluene favors a-glycosylation. 

Since the amides (especially the formamides) are easily cleaved under hydrolysis conditions to amines, the Ritter reaction provides a method for achieving the conversions R OH R NH2 (see 10-32) and alkene R NH2 (see 15-8) in those cases where R can form a relatively stable carbocation. The reaction is especially useful for the preparation of tertiary alkyl amines because there are few alternate ways of preparing these compounds. The reaction can be extended to primary alcohols by treatment with triflic anhydride ° or Ph2CCl" SbClg or a similar salt in the presence of the nitrile. 

Triflates are more reactive than mesylates and tosylates. Triflates are generally prepared by the reaction of alcohols with triflic anhydride in the presence of pyridine at low temperature. In the case where concomitant pyridinium salt formation lowers the yield of the desired triflate, more-hindered bases such as (94) have been used (Scheme 37). ... 

Polymer-supported triphenylphosphine ditriflate (37) has been prepared by treatment of polymer bound (polystyrene-2% divinylbenzene copolymer resin) triphenylphosphine oxide (36) with triflic anhydride in dichloromethane, the structure being confirmed by gel-phase 31P NMR [54, 55] (Scheme 7.12). This reagent is effective in various dehydration reactions such as ester (from primary and secondary alcohols) and amide formation in the presence of diisopropylethylamine as base, the polymer-supported triphenylphosphine oxide being recovered after the coupling reaction and reused. Interestingly, with amide formation, the reactive acyloxyphosphonium salt was preformed by addition of the carboxylic acid to 37 prior to addition of the corresponding amine. This order of addition ensured that the amine did not react competitively with 37 to form the unreactive polymer-sup-ported aminophosphonium triflate. 

Related anchored l,l,3,3-tetraphenyl-2-oxa-l,3-diphospholanium bis-triflate (39) has been prepared by reaction of brominated poly(styrene-co-divinylbenzene) resin 38 with the phosphorous anion generated from l,2-bis(diphenylphosphino)ethane and sodium naphthalenide followed by further oxidation and reaction with triflic anhydride (Scheme 7.13) [55]. This supported reagent has also been employed, to a lesser extent than 37, for the formation of esters and amides by reaction of carboxylic acids with primary alcohols and amines, respectively. 

The desired sulfonate ester is usually prepared by reaction of the alcohol in pyridine with the appropriate sulfonyl chloride, that is, methanesulfonyl chloride (mesyl chloride) for a mesylate, y)-toluenesulfonyl chloride (tosyl chloride) for a tosylate, or trifluoromethane-sulfonyl chloride [or trifluoromethanesulfonic anhydride (triflic anhydride)] for a triflate. Pyridine (C5H5N, pyr) serves as the solvent and to neutralize the HCI formed. Ethanol, for example, reacts with methanesulfonyl chloride to form ethyl methanesulfonate and with yj-toluenesulfonyl chloride to form ethyl /-toluenesulfonate ... 

An intramolecular (4+3)-cycloaddition illustrates the potential of the quasi-Favorskii approach in the preparation of complex ring systerns.Reaction of readily available alcohol 80 with triflic anhydride afforded the cycloadduct 81 stereoselectively in 65% yield (Scheme 7.21 V Treatment of this compound with lithium aluminum hydride (LAH) afforded an essentially quantitative yield of alcohol 82 from a sequence of reduction, quasi-Favorskii rearrangement, and further reduction. 

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