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

Abstract

A metal-free trimolecular [2+2+2] cycloaddition of internal ynamides and nitriles for de novo synthesis of fully substituted pyridines is disclosed. With the versatile Brønsted acid catalyst HNTf2 , the mild intermolecular cyclotrimerization process proceeds with complementary chemoselectivity and excellent regioselectivity.

Retracted Article: An efficient one pot three-component synthesis of 2,4,6-triarylpyridines using triflimide as a metal-free catalyst under solvent-free conditions

“…24 Because of the presence of two strongly electronwithdrawing triuoromethanesulfonyl groups, triimide belongs to the superacid family. In recent years, specically, triimide has been extensively demonstrated as a superb catalyst in miscellaneous cycloaddition reactions such as [ 31) cycloadditions. It is found that triimide has also been used as a catalyst in numerous other organic reactions such as formation of oxime ethers, 32 Mukaiyama aldol reaction, 33 alkylation, 34 synthesis of indanes and tetralins, 35 allyl-allyl cross-coupling, 36 C-C bond formation 37 and Nazarov reaction.…”

Regioselective synthesis of pyridines by redox alkylation of pyridine N-oxides with malonates

“…Classical approaches to the synthesis of pyridines include the Chichibabin [ 5 ] and Hantzsch condensations [ 6 ] and the Kröhnke reaction [ 7 ]. More modern approaches have been reported including a copper-catalyzed annulation reaction [ 8 ] and metal-free cycloaddition reactions [ 9 – 11 ].…”

Metal-free alkene carbooxygenation following tandem intramolecular alkoxylation/Claisen rearrangement: stereocontrolled access to bridged [4.2.1] lactones

“…The reaction proved to be less efficient when it was performed at 60 °C (Table 1, entry 11) or in other solvents 13. The observed excellent efficiency with HNTf 2 as the catalyst can be explained by its high Brønsted acidity combined with the low nucleophilicity of its counterion 15,16…”