Synthesis of pyrazolo[4′,3′:3,4]pyrido[1,2-a]benzimidazoles and related new ring systems by tandem cyclisation of vic-alkynylpyrazole-4-carbaldehydes with (het)aryl-1,2-diamines and investigation of their optical properties

Convenient Synthesis of Pyrazolo[4′,3′:5,6]pyrano[4,3-c][1,2]oxazoles via Intramolecular Nitrile Oxide Cycloaddition

“…We previously investigated the metal-free intramolecular alkyne-azide cycloaddition reaction for the formation of the pyrazolo [4,3-f ] [1,2,3]triazolo [5,1-c] [1,4]oxazepine ring system [26] as well as the synthesis of 2,6-dihydropyrano [2,3-c]pyrazole derivatives by employing the ring-closing metathesis (RCM) reaction [27]. In continuation of our interest in the synthesis and investigation of novel pyrazole-containing polyheterocyclic systems [28][29][30][31][32][33], we report herein the synthesis and structural elucidation of new 3a,4dihydro-3H,7H-and 4H,7H-pyrazolo [4 ,3 :5,6]pyrano [4,3-c] [1,2]oxazole derivatives from appropriate 3-(prop-2-en-1-yloxy)-or 3-(prop-2-yn-1-yloxy)-1H-pyrazole-4-carbaldehyde oximes via the intramolecular nitrile oxide cycloaddition reaction.…”

Synthesis of 2H-furo[2,3-c]pyrazole ring systems through silver(I) ion-mediated ring-closure reaction

“…As a starting material, we used 1-phenyl-1 H -pyrazol-3-ol ( 1 ), which is readily accessible from the oxidation of 1-phenyl-3-pyrazolidinone [ 25 – 26 ]. Recently, we used this scaffold to obtain the 2 H- pyrazolo[4,3- c ]pyridine [ 27 – 28 ], pyrazolo[4,3- f ][1,2,3]triazolo[5,1- c ][1,4]oxazepine [ 29 ] and pyrazolo[4’,3’:3,4]pyrido[1,2- a ]benzimidazole [ 30 ] ring systems as well as to prepare building blocks for the construction of optoelectronic materials and fluorescent organic nanoparticles [ 31 – 34 ].…”

Ring-closing metathesis as a key step to construct 2,6-dihydropyrano[2,3-c]pyrazole ring system

“…As a starting material, we used 1-phenylpyrazol-3-ol (1a), which is readily accessible from the oxidation of 1-phenyl-3-pyrazolidinone. [22][23][24] Recently, we applied this scaffold to obtain the novel pyrazolo [4,3- 25,26 and to prepare building blocks for the preparation of optoelectronic materials and fluorescent organic nanoparticles. [27][28][29][30] The O-allylation of 1a with allyl bromide in the presence of NaH gave O-allylated pyrazole 2a.…”