Triflate group

Highly unstable vinyl cations, generated in situ from vinyl triflates have also been arylated (the triflate group is replaced by the aromatics) to give vinyl aromatics under Friedel-Crafts conditions (28). 

The dinitrogen complex [Os(NH3)5N2]2+ is a useful synthetic intermediate, while the presence of the weakly nucleophilic triflate group enables it to be easily removed in the synthesis of the dihydrogen complex. 

As with rhodium (and cobalt), introduction of five ammonia molecules is relatively straightforward, but the sixth substitution is difficult, requiring more forcing conditions. One versatile route involves the formation of the pentammine triflate complex ion [Ir(NH3)5(03SCF3)]2+, where the labile triflate group is readily replaced by water, then by a range of anionic ligands [148]. 

Polysilanes bearing triflate groups are very reactive and form an insoluble gel with a trace of moisture. The triflate group is hydrolized to silanol which rapidly condenses with the remaining triflate groups to a siloxane unit, linking intra or intermolecularly silicon atoms ... 

Polymers with triflate groups react with alcohols to form alkoxysubstituted polysilanes. This reaction occurs readily in the presence of bases. The best results were obtained using triethylamine and hindered pyridine. In Fig. 3c the NMR spectrum of the reaction mixture containing the excess of triethylamine is shown, the methyl groups from the polymer chains absorb in the range typical for alkoxysilanes. Reaction in the presence of unsubstituted pyridine leads to the formation of insoluble polymer probably by attack at the p-C atom in the silylated pyridine. 

Triflate 880 can be formally considered as an ester of the enol form of ketone 879. Treatment with a base causes elimination of the triflate group to afford l-(benzotriazol-l-yl)alkynes 881 (Scheme 144) <20000L3789>. 

Similar intramolecular hydroarylations of alkynes and alkenes, which obviate the need for a halide or triflate group on the aryl ring, are now well established. Sames group screened over 60 potential catalysts and over 200 reaction conditions, and found that Ru(m) complexes and a silver salt were optimal. This process appears to tolerate steric hindrance and halogen substrates on the arene (Equations (175)—(177)). The reaction is thought to involve alkene-Ru coordination and an electrophilic pathway rather than a formal C-H activation of the arene followed by alkene hydrometallation, and advocates the necessary cautious approach to labeling this reaction as a C-H functionalization... 

The possibility of trapping of the carbocation by a triflate anion followed by substitution of the triflate group by sulfide has also been suggested126, at least for the addition of bicyclic dithioether dications to alkenes and alkynes. 

Initially, glycoside derivatives carrying a triflate group in the 3-position, were subjected to the test. In order to compare the effects of different ester groups, two types of ester-protected galactopyranosides (8,12) were synthesized. 

Similar results were obtained from the epimerization of glycopyranosides where the hydroxyl group in the 4-position was unprotected, and all other positions were protected with either benzoyl or benzyl groups (Scheme 12). Only when an ester group was present at the carbon adjacent to the carbon atom carrying the leaving triflate group did the... 

The triflate of (39) has been converted into the pyrrolidine (4 directly by treatment with ammonia. The 6-configuration, inappropriate for a synthesis of anisomycin, was expected, assuming that displacement of the triflate group is the first stage in the reaction. We have so far been unable to rearrange the 6-isomer (45) into the required a-series. This work is being continued. 

In subsequent studies, methyl vinyl ketone (2.0 mmole) was chosen as the dienophile so as to determine the combined effect of the ionic liquid (2 mL) and the Lewis acids (0.2 and 0.5 wt%) upon the yield and selectivity. Without the Lewis acid catalyst, this system demonstrated a 52% conversion of the cyclopentadiene (2.2 mmol) in 1 h with the endojexo selectivity being 85/15. The cerium triflate-catalyzed reaction was quantitative in 5 min and the endo. exo selectivity was very good for this experiment as well (94 6, endo. exo). Also with the scandium or yttrium salts tested, reactions came to completion in a short time with high stereo-selection. Cerium, scandium and yttrium triflates are strong Lewis acids known to be quite effective catalysts in the cycloadditions of cyclopentadiene with acyclic aldehydes, ketones, quinones and cycloalkenones. These compounds are expected to act as strong Lewis acids because of their hard character and the electron-withdrawing triflate group. On the other hand, reaction times of 1 hour were required for... 

However the most efficient and reliable procedure involved the Sn2 displacement of a triflate group at C-4 of the acceptor with activated 1-thioglycoses. 

The A -(2 -iodobcnzoyl)-aniline bearing a triflate group in the 6 -position was converted selectively to the trifluoromethanesufonyloxy-phenantridone derivative shown in 4.30. The key to the success of the transformation was the proper choice of the base. Silver carbonate left the triflate function intact, while the use of carboxylates led to the appearance of the carbonyloxy... 

TV-Phenyl bistrifluoromethanesulfonimide is a stable solid, and thus an easy reagent with which to work.13 It is also well suited to the introduction of triflate groups on phenols and amines The compound reacts with secondary aliphatic amines, but not with second ary aromatic amines 14... 

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