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

Abstract

Herein, a novel and highly efficient strategy for the synthesis of dihydropyrazoles via Pd-catalyzed carboamination reaction of β,γ-unsaturated hydrazones with alkenyl and aryl halides is demonstrated. The present methodology provides...

Pd/Cu-catalyzed cascade Heck-type reactions of alkenyl halides with terminal alkynes toward substituted pyrrolidine analogues

“…8 Afterwards, the same group described another efficient cascade Heck reaction utilizing diethyl malonate and 1,5-dienes bearing a triflate group at the C2-position for the construction of methylene cyclobutanes and methylene cyclopentanes in good yields. 9 In continuation of our interest in transition-metal-catalyzed cyclization and heterocyclic chemistry, 10 herein, we report a Pd/Cu-catalyzed cascade Heck-type reaction of vinyl bromide-tethered alkenes with terminal alkynes toward highly substituted pyrrolidines (Scheme 1, eqn (2)).…”

Synthesis of Dihydropyrazoles by Pd‐Catalyzed Carboamination of Alkenyl Hydrazones with Aryl Triflates

“…We are also interested in the Pd‐catalyzed carboamination toward dihydropyrazoles. Very recently, we developed an efficient Pd‐catalyzed carboamination of N ‐Ac alkenyl hydrazones with simple aryl and alkenyl halides, delivering alkenyl and aryl‐substituted dihydropyrazoles in good yields [13a] . However, there still lacks general and robust catalyst systems in the cyclization of alkenyl hydrazones toward aryl‐substituted dihydropyrazoles with simple aryl sources.…”

“…Moreover, other Pd sources such as Pd 2 (dba) 3 , PdCl 2 , Pd(OAc) 2 , Pd(acac) 2 and Pd(cod)Cl 2 were not as effective as Pd 2 (dba) 3 •CHCl 3 (Table 1, entries 6-10). Other bases were inferior to K 3 PO 4 (Table 1, entries [11][12][13]. Further screening of solvents such as THF, cyclohexane, CH 3 CN and DCE, and the toluene was found the best choice (Table 1, entries 14-17).…”

Strategies and Methods for the Synthesis of 2‐Pyrazolines: Recent Developments (2012–2022)

“…In contrast to most of the reported methods, an acetyl group was chosen for the protection of the N‐1 nitrogen of the dihydropyrazole 258 . Similar conditions were used to prepare the corresponding pyrazolines 261 from aryl bromides 260 (Scheme 53b) [82a] . Products with similar side groups can also be prepared by Chen and Xiao's protocol, which involves the aminoaroylation of unsaturated hydrazones 262 using diaryliodonium salts 263 as both the aryl source and the oxidant, thus avoiding the use of any external oxidant.…”