Ring formation trifluoromethanesulfonate

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

An entirely different and rather unusual opportunity for the activation of regular C-H fragments was revealed in the course of investigations of certain bicyclic as well as medium-ring-size hydrocarbons. For example, saturated bicyclic hydrocarbon 200 reacts with trifluoroacetic acid, or even acetic acid, at 40 °C with the evolution of hydrogen and the formation of the extremely stable carbocation 201. With the use of trifluoromethanesulfonic acid, a stronger acid, this process takes place almost like a titration even at 0°C (Scheme 4.60). ... 

Urethanes can be cyclised to 1-isoquinolones using trifluoromethanesulfonic anhydride and 4-dimethylaminopyridine it may be that this reagent combination is well suited to the standard formation of 3,4-dihydroisoquinolines too." The cyclisation of urethanes with a combination of phosphorus pentaoxide and phosphoryl chloride is not restricted to substrates with activated benzene rings." ... 

Reaction of phenol derivatives with acyl chlorides in acidic conditions may result in O-acylation or C-acylation, either directly or via a Fries rearrangement. Studies of acylations in acetonitrile using trifluoromethanesulfonic acid (trifllc acid) have shown that O-acylation is favoured at a low acid concentration, while a high acid concentration favours C-acylation. It has also been shown that A-hydroxysuccinimidyl and phenyl esters of benzoic acids are activated by triflic acid and can be used to acylate electron-rich arenes such as ferrocene or pyrene the reactive acylating intermediate is likely to be an acyl triflate or its protonated form. In a polyphosphoric acid medium, the rearrangement of 1,5- 1,8- and 9,10-diacetylanthracenes leads to the formation of the ring-closed product (56). DFT calculations support the conclusion that the reaction involves the intermediacy of 1,9-diacetylanthracene formed under kinetic rather than under thermodynamic control. ... 

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