Triflates triflic anhydride

Trifluoromethanesulfonic (triflic) anhydride is commercially available or can be prepared easily by the reaction of triflic acid with phosphorus pentoxide [66] This moderately hygroscopic colorless liquid is a useful reagent for the preparation of various organic derivatives of triflic acid A large variety of organic ionic triflates can be prepared from triflic anhydride A recent example is the preparation of unusual oxo-bridged dicatiomc salts of different types [SS, 89, 90, 91, 92, 93] (equations 38-44) Stabilized dication ether salts of the Huckel aromatic system and some other systems (equations 38 and 39) can be prepared in one step by the... 

Like the reaction of ketones, the interaction of triflic anhydride with thiourea and substituted thioureas also gives dicationic triflates (equations 40 and 41) however, two sulfur atoms form the bndge in this case This result indicates that triflic anhydride is acting as an oxidizing reagent toward thiourea [89]. 

Oxo-bridged diiodonium triflate [Zefirov s reagent), a useful reagent for the synthesis of triflate esters and iodonium salts, can be prepared by the treatment of lodosobenzene with triflic anhydride [92] or by the reaction of lodobenzene diacetate with tnflic acid [93] (equation 44). 

Bis(3-nitrofurazanoxymethyl)oxetane 221 was synthesized in 52% yield by base-promoted ring closure of the corresponding 3-hydroxy-l-propyl triflate, 219, which is readily available from the diol and triflic anhydride. Oxetane 221 can also be prepared in 74% yield by treatment of the trifurazanyl ether 220 with DBU. Polymerization and copolymerization reactions of oxetane 220 have also been investigated (97MI7) (Scheme 148). 

Asymmetric conjugate addition of dialkyl or diaryl zincs for the formation of all carbon quaternary chiral centres was demonstrated by the combination of the chiral 123 and Cu(OTf)2-C H (2.5 mol% each component). Yields of 94-98% and ee of up to 93% were observed in some cases. Interestingly, the reactions with dialkyl zincs proceed in the opposite enantioselective sense to the ones with diaryl zincs, which has been rationalised by coordination of the opposite enantiofaces of the prochiral enone in the alkyl- and aryl-cuprate intermediates, which precedes the C-C bond formation, and determines the configuration of the product. The copper enolate intermediates can also be trapped by TMS triflate or triflic anhydride giving directly the versatile chiral enolsilanes or enoltriflates that can be used in further transformations (Scheme 2.30) [110],... 

The most versatile approach to disulfonium dications - reaction of triflic anhydride with monosulfoxides of bis-sulfides - has certain limitations in the case of selenium. Most importantly, selenoxides that contain (3-hydrogen atoms are labile.120 122 Trimethylsilyl triflate was used instead of triflic anhydride for synthesis of dication 112 from a selenoxide 111 (Scheme 43).123... 

Methylthio-4-pyrimidinyl triflate (19) and 2-pyrimidinyl triflate (20) were also prepared using triflic anhydride from respective pyrimidones [14], In these cases, triflic anhydride was found to be more convenient than N-phenylmethanesulfonimide (PhNTf2) due to comparative ease of purification of the resulting triflates. 

P-Mannosides are difficult to introduce because the axial C-2 substituent of a mannosyl donor sterically and electronically disfavors nucleophilic attack from the P-face. P-Mannosides have been obtained by the direct substitution of a-glycosyl triflates, which are conveniently prepared by the treatment of an anomeric sulfoxide with triflic anhydride (Tf20) or thioglycosides with NIS (Scheme 4.3a)... 

An a-triflate is formed because this anomer is stabilized by a strong mdo-anomeric effect. Upon addition of an alcohol, the triflate is displaced in an SN2 fashion resulting in the formation of a a-mannoside. A mixture of anomers is obtained when triflic anhydride is added to a mixture of sulfoxide and alcohol. In... 

The most common activator for the glycosyl sulfoxides is trifluoromethanesulfonic anhydride (triflic anhydride), which, in the absence of nucleophiles, rapidly and cleanly converts most sulfoxides into the corresponding glycosyl triflates in a matter of minutes at —78 °C in dichloromethane solution [86,280,315,316]. In the more extensively studied mannopyranose series, only the a-mannosyl triflate is observed by low-temperature NMR spectroscopy (Scheme 4.35) [280]. In the glucopyranose series, mixtures of a- and (1-triflates are observed, in which the a-anomer nevertheless predominates (Scheme 4.36) [280],... 

When triflic anhydride is added to a preformed mixture of glycosyl sulfoxide and acceptor alcohol, it seems apparent that the first formed oxacarbenium ion is directly trapped by the alcohol, without the need for the implication of glycosyl triflates [75,280,323],... 

A variety of other activating systems have been employed for the promotion of sulfoxide-based glycosylation reactions, but none have been studied to the same extent as the triflic-anhydride-mediated reaction [86]. One of the most potent activators, benzenesulfenyl triflate, a by-product of the activation with triflic anhydride, has been shown to bring about rapid conversion of sulfoxides into glycosyl triflates [280]. Unfortunately, this reagent is unstable and has to be prepared in situ from silver triflate and benzenesulfenyl chloride. 

Although the existence of glycosyl triflates has only been demonstrated for the triflic anhydride and benzenesulfenyl triflate promoter systems, presumably the same intermediates may be invoked on preactivation with other triflate-incorporat-ing systems such as TMSOTf (Scheme 4.42) [332] and triflic add (Scheme 4.43) [84,333]. 

An elegant method for the formation of glycosidic bonds from acyclic dithioacetal monosulfoxides and glycosyl acceptors with triflic anhydride has been developed. This method takes advantage of the sulfenyl triflate generated from the reaction of... 

A simplistic view of the mechanism is depicted in Scheme 3.5. The sulfoxide (I) is activated by triflic anhydride to generate a sulfonium salt (III). It was observed early on that the outcome of the glycosylation was not influenced by the configuration at the two variable stereogenic centers in the sulfoxide donor (i.e., anomeric carbon and sulfur).1 This was taken as evidence for the intermediacy of the oxycarbenium ion (V), which arises from rapid elimination of an alkylsulfenyl triflate(IV) from III. Reaction of V with a nucleophile then gives rise to a mixture of a- and P-glycosides (II). 

While triflic anhydride activation of sulfoxides is the norm, other activation procedures have been employed. In the synthesis of the ciclamycin 0 trisaccharide, catalytic triflic acid (TfOH) was employed.19 Trimethylsilyl triflate (TMSOTf), in conjunction with triethyl phosphite (a scavenger for phenylsulfenic acid), has also been used.20... 

Despite these restrictions, the acceptor-bound succinoyl MPEG28 was found to permit glycosylations with glycosyl trichloroacetimidates promoted by boron trifluoride, triflic anhydride, and trimethylsilyl or triethylsilyl triflates, with glycosyl halogenates promoted by silver triflate, and with thioglycosides promoted by the iodonium ion. It is compatible with long-term ester protection, with allylic,... 

These compounds were to be subjected to conventional triflation by triflic anhydride, followed by treatment with potassium nitrite in DMF. It was expected that in all cases good inversion yields would be obtained with neighboring ester groups, whereas the inversion would be inefficient with benzyl groups. 

Telluride 34 was treated with triflic anhydride in the presence of 1 equivalent of DMSO in dichloromethane at room temperature to give Te-(trifluor-omethyl)dibenzotellurophenium triflate (35). Triflate 35 was also synthesized by treating 34 with bromine in l,l,2-trichloroethane at room temperature followed by triflic acid at reflux temperature. Triflate 35 was converted to bromide 36 by treatment with tetrabutylammonium bromide... 

Nitric acid-triflic anhydride is a powerful nitrating agent and probably involves nitronium triflate as the active nitrating agent. ... 

A convenient method for the preparation of nitronium tetrafluoroborate involves treating a mixture of absolute nitric acid or an alkyl nitrate " with anhydrous hydrogen fluoride and an excess of boron trifluoride. Pure nitronium triflate can be synthesized by treating triflic anhydride or triflic acid with dinitrogen pentoxide in an inert solvent. Other methods for nitronium salt synthesis are discussed by Olah. ... 

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%). 

Treatment of the (—)-menthone-derived 2/7-1,3-benzoxazin-4(3//)-one 202 with triflic anhydride gave the triflate 203 in quantitative yield. Palladium-catalyzed cross-coupling of 203 with 2-pyridylzinc halide resulted in formation of an approximately 3 1 mixture of the 4-(2-pyridyl)-2//-l,3-benzoxazine 204 and a 4-imino-l,3-benzodioxane derivative 205 (Scheme 36). Compound 205 was formed by the isomerization of 203, which occurred with complete retention of stereochemistry. The 4-(2-pyridyl)-l,3-benzoxazine derivative 204 was applied in enantioselective allylic alkylations of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate as a chiral ligand inducing a 62% ee in the product <2005JOM(690)2027>. 

CH2C12 (10 mL) containing propane-1,3-diol (3.04 g, 40 mmol) and pyridine (6.94 g, 88 mmol) was added dropwise to a stirred solution of triflic anhydride (24.8 g, 88 mmol) in cold (0°C) CH2C12 (20 mL), The mixture was stirred at 0LC for 30 min then filtered through a 4-cm bed of silica gel to remove pyridinium triflate. The filtrate was concentrated in vacuo at rt to provide a viscous, orange liquid, presumed to be... 

Coupling with enol esters (7, 93). A new synthesis of an alkyl-substituted alkene involves coupling of a lithium dialkyl cuprate with an enol triflate,1 available from a ketone by reaction with triflic anhydride and 2,6-di-t-butylpyridine.2 A wide variety of organocuprates can be used and the geometry of the enolate is largely retained. Reported yields are in the range 60 100%. 

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