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Recent Advances in the Chemistry of Indazoles

“…Michael‐type additions between hydrazine groups and alkynyl groups, as presented in Scheme , can be used to prepare the indazole nucleus 106. Here, o ‐chloro‐alkynylarenes 89 were starting materials to synthesize 90 .…”

Copper(I) Alkyne and Alkynide Complexes

“…283 The heterocyclization of (o-(arylethynyl)aryl)hydrazines as a novel synthesis method for the preparation of functionalized 1H-and 2H-indazoles as well as indoles on the basis of the reaction of 2-substituted indazoles with copper(I) alkynides in pyridine or DMF as solvent was also reported. 284 The one-pot preparation of 5-nitroisocoumarins from tandem Castro−Stephens couplings of aryl alkynes with 2-iodo-3-nitrobenzoic acid followed by copper(I)-catalyzed cyclization of the intermediate to form 2-arylalkynyl-3-nitrobenzoic acids was reported in 2006 by the group of Threadgill. 285 NMR and X-ray crystallography indicated the cyclization to be 6-endo, which is in contrast with earlier reports of 5-exo cyclization of analogous 2-iodobenzoate esters with alkynes.…”

“…Nevertheless, it was observed that the catalytic Sonogashira Pd/Cu/NEt 3 system has the advantage of allowing the cross-coupling under milder reaction conditions but partial conversion of the alkynes to oxidative homocoupling products may occur . The heterocyclization of ( o -(arylethynyl)­aryl)­hydrazines as a novel synthesis method for the preparation of functionalized 1 H - and 2 H -indazoles as well as indoles on the basis of the reaction of 2-substituted indazoles with copper­(I) alkynides in pyridine or DMF as solvent was also reported . The one-pot preparation of 5-nitroisocoumarins from tandem Castro–Stephens couplings of aryl alkynes with 2-iodo-3-nitrobenzoic acid followed by copper­(I)-catalyzed cyclization of the intermediate to form 2-arylalkynyl-3-nitrobenzoic acids was reported in 2006 by the group of Threadgill .…”

Transition Metal‐Catalyzed Synthesis of Fused Five‐Membered Aromatic Heterocycles

“…For instance, Katritzky utilized this chemistry to obtain benzotriazolyl-substituted indoles, valuable intermediates in the synthesis of fused and polycyclic indole-derived structures [244,245]. Shvartsberg used Castros protocol for the assembly of benz[g]indolediones [246], whereas the synthesis of pharmacologically important 1-aminoindole derivatives was reported by Prikhodko [247,248].…”