Triflimide

Metal‐Free [2+2+2] Cycloaddition of Ynamides and Nitriles: Mild and Regioselective Synthesis of Fully Substituted Pyridines

“…HCl also did not show appreciable catalytic ability in spite of its strong acidity.H owever, triflic acid (HOTf) exhibited dramatically higher catalytic activity leading to the pyridine 3aa in 88 %y ield. Gratifyingly,t riflimide (HNTf 2 ) [9] was found to be even more effective (entry 5). [10] Next, we evaluated other reaction parameters.Alower catalyst loading led to decreased reaction rate,b ut the selectivity remained excellent (entry 7), and was also observed with either alower concentration or other solvents (entries 8a nd [10][11][12].…”

“…Under the established reaction conditions ( Table 1, entry 6), ynamides with various N-sulfonyl groups all participated in the pyridine-formation reaction with good efficiency ( Table 2). Thestructure of the pyridine 3da was confirmed by X-ray crystallography.Awide range of N-Ts-substituted ynamides with various substituents also smoothly participated in the process with excellent regiocontrol (Table 3), although some of them required ah igher temperature,p resumably because of the increased steric hindrance (entries [8][9][10][11][12]. A terminal ynamide was also found to be suitable,a lbeit in amoderate yield (entry 13).…”

“…Notably,the strong acidic conditions showed impressive functional-group compatibility (e.g.,TBS-protected alcohols,ethers,esters,alkenes,alkynes, bromoalkynes). It is also worth noting that, instead of intramolecular cyclization,t hose nitriles tethered with an alkene or alkyne still proceeded intermolecularly to form the pyridines 3ag-aj (entries [6][7][8][9]. Finally,t hiocyanate is also as uitable reaction partner leading to the 2-sulfenylpyridine 3ak.…”

Triflimide (HNTf2) in Organic Synthesis

“…Since its first synthesis in 1984, the study and exploitation of triflimide has evolved tremendously over the years. Prior to this Review, there have been sporadic introductory articles on this acid. , For example, Takasu reviewed specifically on triflimide-catalyzed cycloaddition reactions as well as their applications in the synthesis of azaheterocycles and related molecules . Yamamoto and Akiyama , have also had excellent review articles on strong Brønsted acids with special efforts devoted to some important reactions promoted by triflimide.…”