Mn- and Co-Catalyzed Aminocyclizations of Unsaturated Hydrazones Providing a Broad Range of Functionalized Pyrazolines

Abstract

Manganese- and cobalt-catalyzed aminocyclization reactions of unsaturated hydrazones are reported. Whereas manganese catalysis provides access to pyrazoline and tetrahydropyridazine alcohols, cobalt catalysis for the first time paves the way for the selective formation of pyrazoline aldehydes. Furthermore, various functional groups including hydroperoxide, thiol derivatives, iodide, and bicyclopentane may be introduced via manganese-catalyzed ring-forming aminofunctionalization. A progesterone receptor antagonist was prepared using the aminocyclization protocol.

Cobalt-Catalyzed Cyclization of UnsaturatedN-Acyl Sulfonamides: a Diverted Mukaiyama Hydration Reaction

“…We have been interested in identifying novel reactivity of olefins mediated by base metal–salen complexes. ,,, In the presence of a Co II catalyst, silane, and oxidant, olefins classically proceed through Mukaiyama hydration pathways (Figure B). When we subjected N -acyl sulfonamide 3a to Mukaiyama hydration conditions, a mixture of products I and II was formed in 46% and 4% yield, respectively, in line with early observations by Mukaiyama. − , Interestingly, when Co­(acac) 2 was replaced by Co III (salen)­OTf complex 1 under otherwise identical conditions, the formation of N -sulfonyl imidate 4a was observed (36%).…”

Synthesis of dihydropyrazoles enabled by Pd-catalyzed carboamination of alkenyl hydrazones with alkenyl and aryl halides

“…In this regard, owing to their unique properties and high reactivity, alkenyl hydrazones have emerged as alternative precursors for the construction of functionalized dihydropyrazoles. 5–8 Among the existing methods, most are based on radical-mediated annulation. For example, Loh's group developed a radical mediated diamination of alkenes with phenylhydrazine and azodicarboxylates to afford highly functionalized trans -diamines.…”

“…5 a Recently, Carreira further developed a new method for the synthesis of 4,5-dihydropyrazoles via manganese- and cobalt-catalyzed aminocyclization reactions of unsaturated hydrazones. 8 On the other hand, palladium-catalyzed carboheterofunctionalisations of alkenes have witnessed significant advancements for the construction of nitrogen-containing heterocycles. 9,10 Remarkably, Xiao and Chen's group realized palladium( ii )-catalyzed aminoarylation of β,γ-unsaturated hydrazones in the presence of Ar 2 IBF 4 , in which the Pd–C bond is captured and Pd II is oxidised to Pd IV , promoting C–C bond formation (Scheme 1a).…”

Stereoselective synthesis of the isoxazolidine ring via manganese(iii)-catalysed aminoperoxidation of unactivated alkenes using molecular oxygen in air under ambient conditions

“…19 Both reactions need stoichiometric amounts of a base and expensive TEMPO as terminal oxidants or toxic CHCl 3 as a hydrogen source and solvent. However, those intramolecular N–C bond formation reactions for constructing isoxazolidine rings, including other heterocyclic construction reactions, 20,21 do not directly incorporate O 2 into the substrates.…”