Preparation of pyrazoles and pyrazolines by the reaction of chlorocyclopropanols with hydrazines in the presence of crown ethers

Aqueous N-Heterocyclization of Primary Amines and Hydrazines with Dihalides: Microwave-Assisted Syntheses of N-Azacycloalkanes, Isoindole, Pyrazole, Pyrazolidine, and Phthalazine Derivatives

“…The syntheses of dihydroisoindole derivatives include borane−THF reduction of phthalimide, multistep metalation−alkylation of formamidine, reductive amination of phthaldehyde by tetracarbonylhydridoferrate, and catalytic N-heterocyclization using a Cp*Ir complex . The standard preparation of 4,5-dihydropyrazoles involves the cyclocondensation of hydrazine derivatives with α, β -unsaturated carbonyl compounds or the reaction of hydrazine with substituted cyclopropanes, often requiring the use of a crown ether as a phase-transfer catalyst . Pyrazolidines are usually prepared by the condensation reaction of hydrazines with β-diketones or β-ketoesters or alternatively by reacting a protected hydrazine, di- tert -butyldihydrazodiformate, with 1,3-dibromopropane in the presence of a phase-transfer catalyst ultimately requiring a sequential deprotection of the Boc group in 4 M HCl .…”