A Base‐Promoted Tandem Cycloaddition/Air Oxidation Reaction of Electron‐Deficient Conjugated Enynes and Hydrazines: Synthesis of Highly Substituted Pyrazoles

Abstract

Rapid access: A base-mediated cycloaddition/oxidation reaction of hydrazines and electron-deficient 1,3-conjugated enynes gives pyrazole derivatives, some of which are not easily accessible by other methods (see scheme). The reaction conditions are mild, thus enabling a variety of functional groups to be tolerated.

Tailored Palladium Catalysts for Selective Synthesis of Conjugated Enynes by Monocarbonylation of 1,3‐Diynes

“…[27] The similar reaction was performed by using hydrazine and K 2 CO 3 , affording pyrazole compound 9 a in 82 % yield. [28] Interestingly, when using 5 fa under the same conditions, the trimethylsilyl group was removed and product 9 b was afforded in 80 % yield. Treatment of 3 aa with diethyl aminomalonate hydrochloride and DBU provided the 2,3-dihydro-1H-pyrrole 10 a via a formal [3+2] cycloaddition.…”

Tailored Palladium Catalysts for Selective Synthesis of Conjugated Enynes by Monocarbonylation of 1,3‐Diynes

“…[27] Thes imilar reaction was performed by using hydrazine and K 2 CO 3 ,a ffording pyrazole compound 9a in 82 %y ield. [28] Interestingly,w hen using 5fa under the same conditions,t he trimethylsilyl group was removed and product 9b was afforded in 80 %y ield. Tr eatment of 3aa with diethyl aminomalonate hydrochloride and DBU provided the 2,3-dihydro-1H-pyrrole 10 a via af ormal [3+ +2] cycloaddition.…”

Gas-phase UV absorption spectra and OH-oxidation kinetics of 1H-1,2,3-triazole and pyrazole

“…Indeed the Comprehensive Medicinal Chemistry (CMC) database lists more than 67% of compounds contain heterocyclic rings as pesticides (insecticides, fungicides) as well as antiviral and antibacterial agents. [4][5][6][7] Furthermore, these compounds are also used as in several industrial applications such as in polymers, 8 corrosion inhibitors, 3,9 ligands for transition metals, 10,11 cosmetic colorings, 2,8,12 solvents, antioxidants and UV stabilizers. 8,12,13 Hence, the usage of such nitrogen heterocycles species leads to their release into the atmosphere.…”