Triflic anhydride initiation

It was long believed that cationic polymerization was an unsatisfactory route to synthesize well-defined functional polymers because of inter- or intra-molecular transfer or rearrangement However, in recent years, several monomers have exhibited sufficient control of initiation, propagation and termination to allow the synthesis of functional polymers. Tetrahydrofuran (THF) has been cationically polymerized using the difunctional initiator triflic anhydride (Scheme 4). ... 

The Boekelheide reaction has found utility in other synthetic methodology. An approach to 2,3-pyridynes made use of this chemistry in the preparation of the key intermediate 30. Treatment of 28 with acetic anhydride produced the desired pyridone 29. Lithiation was followed by trapping with trimethylsilyl chloride and exposure to triflic anhydride gave the pyridyne precursor 30. Fluoride initiated the cascade of reactions that resulted in the formation of 2,3-pyridyne 31 that could be trapped with appropriate dienes in Diels-Alder reactions. 

Finally, a carbocyclic ring formation initiated by a keteniminium cyclization is depicted in Scheme 1.8 [6]. In the presence of triflic anhydride and DTBMP, pyrrolidine amide 1-20 was converted into the keteniminium ion 1-22, traversing inter-... 

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%). 

Bis(iodosyl)benzene reacted with triflic anhydride to afford a bis iodine (III) derivative [21], DIB or iodosylbenzene, however, do not afford with triflic acid, or its anhydride, the expected analogues of HTI, although these are initially formed. The reaction of iodosylbenzene and triflic anhydride leads to two different products, depending on reaction time. When triflic acid was allowed to react with iodosylbenzene in dichloromethane for about 20 min the yellow p-compound 1 (m.p. 100-110°C) was obtained it was the same with the so-called Zefirov s reagent, which was originally prepared from DIB and triflic acid in chloroform. When the reaction time was extended to 12 h, then 1 isomerized to the slightly pale yellow compound 2 (m.p. 125-132°C). For preparative purposes the direct reaction of iodosylbenzene with triflic acid was preferable for 2, since it was isolated in 94% yield. 

Triflic anhydride is an efficient initiator used in thfe living polymerization of oxolane 60), and bifunctional poly-THF oligomers can be further employed to initiate the polymerization of t-butylaziridine yielding polymers with aziridinium sites at both ends of their chain61 which can be reacted with methacrylic acid. 

A new approach to the synthesis of annulated sulfur heterocycles based on triflic anhydride-promoted electrophilic cyclization of the hetaryl-containing alkyl sulfides, including 1409, was elaborated <2003S1191>. The proposed method includes intermediate formation of sulfonylsulfonium salts 1410 followed by electrophilic attack on the aromatic ring (Scheme 271). Smooth demethylation of initially formed cyclic sulfonium salts 1411 by treatment with EtsN afforded a number of five- 1412 and six- 1413 membered fused sulfur heterocycles. Unexpected ring opening with formation of compound 1414 took place in the reaction of diethylamine with five-membered sulfonium salt 1411. 

Esters of very strong protonic acids (trifluoromethanesulfonic, fluoro-sulfonic, perchloric), however, are sufficiently strong alkylating agents to initiate the polymerization of even weakly nucleophilic monomers (cyclic acetals, ethers) [2-6], Also their anhydrides (e.g., triflic anhydride) are efficient initiators. This last compound is especially interesting, because in the polymerization of cyclic ethers it leads to macromolecules with two identical growing chain ends (difunctional initiator) [30] ... 

Anhydrides of strong i x)tonic acids provide a group of initiators able to give dicationically terminated macromolecules °° The anhydride of trifluoromethane-sulfonic acid (triflic anhydride) initiates the polymerization of THF in this way both reactions, with rate constants ki and kai, are faster than the formation of the alkyltetrahydrofuranium cation with the corresponding triflic acid ester ... 

Neither the first nor the second step in Scheme (42) has been directly observed, but it has conclusively been shown by studies of the number of the end groups in poly-THF initiated with triflic anhydride that one molecule of the anhydride gives two growing ends of the cationic and/or ester structure in one macxomolecufe. These structures are interconvertible. Recently, Smith separated and characterized two intmnediate products tetramethylene-bis-triflate, resulting from the attack of the anion on the o-methylene carbon atom in salt 42a, and the corresponding dicationic trimer... 

Unfortunately, there are no data for triflic anhydride (CF3802)20 available which, according to the existing reports, gives rise to much faster initiation than esters. 

The formation of 1-oxocyclopropyllithium compounds can also be accomplished starting from 1-alkoxyphenylsuIfanylcyclopropanes using lithium 1-dimethylaminonaphthalenide (LDMAN). The effectiveness of this procedure is illustrated starting from 1-methoxy-l-phenylsulfanyl-cyclopropane (53) giving cyclobutanones 56. An efficient method to initiate cyclopropylmethyl to cyclobutane ring expansion of these cyclopropanes under neutral conditions uses triflic anhydride in dichloromethane in the presence of 2,6-di-rer -butyl-4-methylpyridine. ... 

Table 15.9. Calculated and measured number average molecular weight of polymers isolated after first and second stage of sequential polymerization of 1,3-dioxolane and 1,3-dioxepane initiated by triflic anhydride. [M]o (A and B) from 2 to 3 mol I 1, [I]q from 10"3 to 10 2 mol 1 1109>...

Chiral indole-2-sulfoxides have been employed by Feldman and Karatjas for asymmetric spirooxindole synthesis [70]. In one example, treatment of 115 with triflic anhydride initiated a Pummerer-type cyclization of the silyl enol ether side chain onto C3 (Scheme 30). Sequential hydrolysis of the resulting thioimidate intermediate with aqueous HgCl2 afforded the spirocyclohexanone functionalized oxindole 116 in modest yield and enantioselectivity at —78°C (33, 67% ee). Improved selectivity (58, 86% ee) was observed at lower reaction temperature (-110°C). 

PolyDXL bis-macromonomers were prepared by cationic polymerization of DXL initiated by triflic anhydride, end-capping of the resulting biftmctional living polymers with triethylamine, and nucleophilic substitution of ammonium end groups by a methacrylate anion. ... 

Polyacetals containing polymerizable acrylate groups at both ends were also prepared (but not fully characterized) by cationic polymerization of DXL initiated with triflic anhydride in the presence of HEMA (hydroxyethyl methacrylate). Radical copolymerization of those bis-macromonomers with acrylic acid led to degradable pH-sensitive networks. ... 

The three-membered aziridine rings and the four-membered azetidine rings can only be polymerized by a cationic mechanism." Although triflic anhydride initiation does not lead to bifunctional polymers, monofunctional telechelics can be obtained from t-butylaziridine (TBA) using... 

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