Trifluoromethanesulfonic acid reaction with alkenes

Various alkenes react with diphenyl diselenide/(NH4)2S208, in an aqueous acetonitrile as a solvent in the presence of trifluoromethanesulfonic acid to afford the amidoseleny-lation products. It has been observed that some unsaturated nitriles in dioxane undergo intramolecular cyclization reaction to give the corresponding phenylselenolactones. 

Aminoselenenylation of alkenes occurs when adducts from the reaction with phenylselencnyl chloride are allowed to react further in aqueous solution containing alkanenitriles and strong acids such as trifluoromethanesulfonic acid. Incorporation of the alkanenitrile followed by hydrolysis of the nitrile function affords /1-phcnylscleno carboxamides64. 

Table 9. /3-Acylaminoalkyl or /5-Acylaminocycloalkyl Phenyl Selenides by Reaction of Alkenes with Phenylselencnyl Chloride, Nitriles, Trifluoromethanesulfonic Acid, and Water64...

Hydrazoic acid is conveniently prepared in situ by hydrolysis of azidotrimethylsilane over silica gel. Only a catalytic amount of trifluoromethanesulfonic acid is required to achieve the hydroazidation of cyclic alkenes the completion of the reaction is preferentially controlled by gas-chromatographic analysis, as prolonged reaction time causes the partial decomposition of the organic azide by the acid catalyst. From norbornene the exo-azide 5 was exclusively produced, but no diastereoselectivity was observed with 1,2-dimethylcyclohexene106. 

The reaction of alkenes with acetyl hypofluorite436 439 or with fluorine,451-473-4 74 2,3,4,5,6-pentachloro-l-fluoropyridinium trifluoromethanesulfonate (A -FPCPy-OTf),441 711 cesium fluoroxysulfate,435 (V-fluorobis(triflyl)amine432 or l-(chloromethyl)-4-fluoro-l,4-diaza-bicyclo[2.2.2]octane tetrafluoroborate431 in acetic acid leads to the simultaneous addition of fluorine and the acetoxy group across the double bond. Examples of these additions are summarized in Table 34. Further examples are the formation of l439 and 2.439... 

The acid-promoted intramolecular Schmidt reaction of azido-alkene 114 is featured in the formal synthesis of gephyrotoxin. Treatment of 114 with trifluoromethanesulfonic acid followed by L-Selectride reduction of the resultant iminium ions 115 and 116 generates a mixture of diastereomeric bromo-amines. The bromide is replaced with acetate ion, and the acetate is reduced to give alcohol 117, a known intermediate in the synthesis of gephyrotoxin. 

The addition of HN3 to nonactivated alkenes with formation of the saturated azides requires drastic conditions and a catalyst. Olefinic double bonds activated by conjugated, electron-withdrawing groups like -CN, -NO2, or -C(0)R react easily [8, 9]. The photolysis [10] and the pyrolysis [7] of HN3 with alkenes yields nitriles, N2, and decomposition products. The reaction of HN3 with alkines usually leads to 1,2,3-triazoles. Single or double addition with formation of vinyl azides or saturated diazides are rare [8, 9]. Arenes and HN3 form aniline derivatives directly and efficiently in the presence of trifluoroacetic acid and the strongly acidic trifluoromethanesulfonic acid [11]. The yield is frequently low in the presence ofH2S04[1]. 

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