Triflate ester

The alkaloid dubamine contains a single bond between the two heteroarene units. This lond was formed in 79% yield by the generally valuable palladium-catalyzed eoupling of an ryltrimethylstannane with an aryl triflate (see section 1.6). The requisite stannane was pre-ared from l,3-benzodioxol-5-yl triflate and hexamethyldistannane with the same palladium atalyst, the triflate ester was obtained from 2(1 f/)-quinolinone and trifluoromethanesulfonic jihydride (A.M. Echavarren, 1987). An earlier attempt to perform this aryl coupling by dassical means gave a yield of only 1 %. 

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). 

Tnflrc anhydride is a useful reagent for the preparation of covalent triflate esters from alcohols, ketones, and other organic substrates [66] In many cases, very reactive triflates can be generated m situ and subjected to subsequent transformation without isolation [94, 95, 96, 97] Typical examples are cyclization of amides into dihydroisoqumolines (equation 45) and synthesis of Al-hydroxy-a-amino acid denvatives (equation 46) via the intermediate covalent triflates... 

Another triflate ester that recently has found growing application in organic synthesis is commercially available trimethylsilylmethyl trifluoromethanesul fonate. This powerful alkylating reagent can be used for the synthesis of various methylides by an alkylation-desilylation sequence A representative example is the generation and subsequent trapping by 1,3-dipolar cycloaddition of indolium methanides from the corresponding indole derivatives and trimethylsilylmethyl trifluoromethanesulfonate [108] (equation 54)... 

An interesting class ot covalent Inflates are vin l and ar>/ or heteroaryl Inflates Vinyl inflates are used for the direct solvolytic generation of vinyl cations and for the generation of unsaturated carbenes via the a-elimination process [66] A triflate ester of 2-hydroxypyridine can be used as a catalyst for the acylation of aromatic compounds with carboxylic acids [109] (equation 55)... 

A large variety of salts of triflic acid formed both from metals and nonmetals are known Many of these salts are versatile reagents for organic synthesis because of such properties of the tnflate anion as very low nucleophilicity and low coordinating ability However, despite low nucleophilicity, the triflate anion can combine with carbocationic intermediates under appropriate conditions to form triflate esters [116, 117, II8. ... 

The second element of general importance in the synthesis of a task-specific ionic liquid is the source of the functional group that is to be incorporated. Key to success here is the identification of a substrate containing two functional groups with different reactivities, one of which allows the attachment of the substrate to the core, and the other of which either is the functional group of interest or is modifiable to the group of interest. Functionalized alkyl halides are commonly used in this capacity, although the triflate esters of functionalized alcohols work as well. 

The Z- or -configuration of the vinyl groups of linchpins (106,107) is preserved when the stannyl groups are displaced by triflate esters, as shown in reactions 49 and 50301. 

A further advantage of our treatment of the styrene results is that we can obtain a first-ever estimate of the minimum value of kpE for the poly(styryl)triflate ester of ca. 750 TmoH-s"1 (from kpE = RE/m-[E], assuming that [E] = [HA]J, which is ca. 100 times as great as the kpu for poly(styryl)perchlorate ester. 

TBA-HS04 (0.6 g, 1.77 mmol) is added to the inflate sugar (0.85 mmol) in MeCN (15 ml) at 0°C and the mixture is stirred at room temperature until TLC analysis indicates complete consumption of the triflate ester (ca. 12 h). The solvent is evaporated and the residue recrystallized to yield the hydrogensulphate ester or the cyclic ester. 

Voelter and co-workers synthesized the nitrate esters of some carbohydrates by treating the corresponding trifluoromethanesulfonate (triflate) esters with tetrabutylammonium nitrate. Yields were generally excellent. The same authors describe a one-pot process for the synthesis... 

A. Synthesis of triflate esters with triflic anhydride 97. . 

B. Synthesis of a triflate ester with trifiyl chloride 97... 

C. Synthesis of a Reactive Triflate Ester in the Presence of a Nonnucleophilic Base, 2,6-Di-ferf-butyl-4-methylpyridine [7] ... 

Vinyl Substitution with Triflate Esters and Related Esters 858... 

Work by Sigwalt, Bischoff and Cypryk22 have used this inter-and intramolecular catalysis to explain the condensation kinetics and cyclic formation processes in siloxane condensations. The kinetics show a very complex dependence on siloxane chain length, complicated by equilibria involving acid, silanol and water. They do indicate that the dominating reaction in the process is condensation and that chain disproportionation and chain scrambling are negligible The kinetics of condensation are influenced by the involvement of triflic acid in several equilibria, i.e. the formation of triflate esters, shown in equation 3, the possible involvement of triflic acid in the reaction of these esters with silanol, shown... 

Several different nucleophilic displacement reactions of ring substituents were utilized in the synthesis of 3-azido-oxetane-2-carboxylates (Scheme 12) <2001TL4247>. The triflate ester 66, prepared from the corresponding trans-/3-hydroxy ester and triflic anhydride, was displaced by reaction with sodium azide, and inversion of configuration, to... 

Analogues of 70 have been prepared by various methods including nucleophilic displacement of triflate esters attached directly to the oxetane ring (see Section 2.05.7.2) <2001TL4247>, from xylose, 145, via the benzyl-idene-protected oxetane, 146 (Scheme 24) <2004TA2667>, or from L-rhamnose, 147, via a l,4-lactone-2-O-triflate, 148 (and key oxetane 149 (Scheme 25)) <2004TA2681>. The /3-azidoester monomers formed by these methods were converted to the /3-amino acids and subsequently to /3-peptides by reduction of the azide and ester hydrolysis. 

Benzo[a] and benzo[c] xanthene and dibenzo[a,c]xanthene have been synthesised by the Pd-catalysed cyclisation of aromatic 2-(arylmethyl)phenol triflate esters through S-0 bond cleavage <02T5927>. 

The related reagent tris(dimethylamino)sulfonium trifluoromethoxide [TASfCFjO)], which is suitable for the synthesis of primary 0-trifluoromcthyl carbohydrates from triflates, gives predominantly fluorination in the case of the secondary triflate ester of 1.2 5,6-di-0-iso-propy lidene-x-u-allofuranose. probably due to partial decomposition of the reagent in refluxing acetonitrile. ... 

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