DMAP Catalyzed Domino Rauhut–Currier Cyclization Reaction between Alkylidene Pyrazolones and Nitro-olefins: Access to Tetrahydropyrano[2,3-c]pyrazoles

Abstract

Herein, we employ unsaturated pyrazolones in the Rauhut–Currier reaction for the first time. A domino Rauhut–Currier cyclization reaction has been developed between unsaturated pyrazolones and nitro-olefins. The trisubstituted tetrahydropyrano­[2,3-c]­pyrazoles were obtained in moderate to high yields with excellent diastereoselectivities. A few applications including a synthesis of disubstituted tetrahydropyrano­[2,3-c]­pyrazole have been demonstrated. A preliminary catalytic asymmetric version of this process was also studied with chiral DMAP catalysts.

The Last Fortress of Tin's Tyranny – Protodenitration of Nitroalkanes

“… Applications of the Ono‐Tanner reaction between 2019 and 2021 by Wang and Guo (2019), [213] Yuan (2019), [214] Yuan (2019), [215] Valeev (2020), [216] Seidel (2020), [217] Cobb (2020), [218] Wang and Guo (2020), [219] Zhang (2020), [220] Pan (2021), [221] Norrby and Wärnmark (2021), [222] Matsuo (2021), [223] and Corey (2021) [224] …”

Recent Developments in Intermolecular Cross‐Rauhut‐Currier Reactions

“…To obtain tetrahydropyrano[2,3 c] pyrazoles, the Pan group developed a DMAP catalysed domino RauhutCurrier cyclization reaction between alkylidene pyrazolones and nitro‐olefins in 2021 (Scheme 18). [14] The reaction was performed between unsaturated pyrazolone 36 and nitrostyrene 37 in toluene at ambient temperature with DABCO. Eventually, the optimum catalyst for this reaction was found to be DMAP (20 mol%).…”

Chemo- and regioselective defluorinative annulation of (trifluoromethyl)alkenes with pyrazolones: synthesis and insecticidal activity of 6-fluoro-1,4-dihydropyrano[2,3-c]pyrazoles

“…Owing to their diverse important biological activities, the synthesis of functionalized dihydropyrano[2,3- c ]pyrazole scaffolds has been extensively investigated. 5 Despite these advances, monofluoroalkene decorated dihydropyrano[2,3- c ]pyrazoles have never been synthesized or tested, probably due to the lack of protocols for their preparation.…”

“…8,9 On the other hand, commercially available pyrazolones have been extensively used for the synthesis of functionalized dihydropyrano[2,3- c ]pyrazole scaffolds. 5 We assumed that the defluorinative functionalization reaction of (trifluoromethyl)alkenes with pyrazolones might become a straightforward pathway to access novel monofluoroalkene decorated dihydropyrano[2,3- c ]pyrazoles. However, due to the availability of many nucleophilic sites resulting from their tautomeric structures (O–H form, C–H form, and N–H form), this reaction remains an attractive but unsolved challenge, and a reliable strategy is necessary to distinguish these nucleophilic sites to ensure the selectivity and efficiency of the reaction (Scheme 1b).…”