Palladium-Catalyzed Synthesis of Polysubstituted Pyrazoles by Ring-Opening Reactions of 2H-Azirines with Hydrazones

Synlett ◽  
2020 ◽  
Author(s):  
Jiaan Shao ◽  
Ke Shu ◽  
Wenteng Chen ◽  
Shuangrong Liu ◽  
Huajian Zhu ◽  
...  
Keyword(s):  
Ring Opening ◽  
Chemical Conversion ◽  
Alternative Route ◽  
Ring Opening Reaction ◽  
Ring Opening Reactions ◽  
Palladium Catalyzed ◽  
Plausible Mechanism

AbstractA palladium–catalyzed ring-opening reaction of 2H-azirines with hydrazones has been developed. This protocol provides an alternative route for the construction of various polysubstituted pyrazoles with a wide substrate scope. Moreover, a plausible mechanism is proposed for this reaction, which should further enrich the chemical conversion of 2H-azirines.

scholarly journals Torquoselectivity of the Ring-Opening Reaction of 3,3-Dihalosubstituted Cyclobutenes: Lone Pair Repulsion and Cyclic Orbital Interaction

2019 ◽  
Author(s):  
Yuji Naruse ◽  
Atsushi Takamori
Keyword(s):  
Double Bond ◽  
Ring Opening ◽  
Lone Pair ◽  
Repulsive Interaction ◽  
Orbital Interaction ◽  
Ring Opening Reaction ◽  
Ring Opening Reactions ◽  
Major Factors ◽  
Vacant Orbital ◽  
Model Reactions

<div><div>Three major factors determine torquoselectivity, which is the diastereoselectivity in electrocyclic ring-opening reactions to produce <i>E</i>/<i>Z</i>-double bond(s). One is the interaction between the decomposing s<sub>CC</sub> bond and low-lying vacant orbital(s), such as a p*- or s*-orbital on the substituent, which promotes the reaction, resulting in inward rotation of the substituent. Second, for a substituent with a lone pair(s), repulsive interaction between the decomposing s-bond and the lone pair(s) hinders inward rotation, so that the products of outward rotation should be preferred. Finally, a more strongly donating s-electron-donating group (sEDG) rotates inwardly due to stabilization by phase-continuous cyclic orbital interaction. We compared the latter two interactions, repulsion between the lone pairs on the substituent and stabilization from phase-continuous cyclic orbital interaction, to determine which has a greater effect on the diastereoselectivity. We considered a series of model reactions with halogen substituents, and concluded that the diastereoselectivity is mainly controlled by cyclic orbital interaction.<br></div></div>

scholarly journals Asymmetric ring-opening reaction of meso-epoxides with aromatic amines using homochiral metal–organic frameworks as recyclable heterogeneous catalysts

RSC Advances ◽  
2018 ◽  
Vol 8 (49) ◽  
pp. 28139-28146 ◽  
Author(s):  
Koichi Tanaka ◽  
Maya Kinoshita ◽  
Jun Kayahara ◽  
Yutaro Uebayashi ◽  
Kazusada Nakaji ◽  
...  
Keyword(s):  
Aromatic Amines ◽  
Ring Opening ◽  
Heterogeneous Catalysts ◽  
Metal Organic Framework ◽  
Metal Organic Frameworks ◽  
Amino Alcohols ◽  
Ring Opening Reaction ◽  
Ring Opening Reactions ◽  
Metal Organic ◽  
Asymmetric Ring Opening

Asymmetric ring-opening reactions of meso-epoxides by aromatic amines were achieved by using some chiral metal–organic frameworks. The corresponding β-amino alcohols were obtained with good yields and enantioselectivities (up to 97% ee).

scholarly journals Regioselective palladium-catalyzed ring-opening reactions of C1-substituted oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylates

2016 ◽  
Vol 12 ◽  
pp. 239-244 ◽  
Author(s):  
Michael Edmunds ◽  
Mohammed Abdul Raheem ◽  
Rebecca Boutin ◽  
Katrina Tait ◽  
William Tam
Keyword(s):  
Ring Opening ◽  
Optimal Conditions ◽  
Aryl Iodides ◽  
Ring Opening Reactions ◽  
Palladium Catalyzed

Palladium-catalyzed ring-opening reactions of C1 substituted 7-oxanorbornadiene derivatives with aryl iodides were investigated. The optimal conditions for this reaction were found to be PdCl2(PPh3)2, ZnCl2, Et3N and Zn in THF. Both steric and electronic factors played a role in the outcome of the reaction as increasing the steric bulk on the bridgehead carbon decreased the yield. These reactions were found to be highly regioselective, giving only one of the two possible regioisomers in all cases. A diverse collection of novel, highly substituted biphenyl derivatives were obtained.

Thiophene Ring-Opening Reactions III: One-Pot Synthesis and Antitumor Activity of 1,3,4-Thiadiazoline–Benzothiazolo[3,2-b]pyridazine Hybrids

2021 ◽  
Vol 18 ◽  
Author(s):  
Ahmad Ahmad Abdullah ◽  
Jalal Zahra ◽  
Salim Sabri ◽  
Firas Awwadi ◽  
Mohammed Abadleh ◽  
...  
Keyword(s):  
Ring Opening ◽  
Thiophene Ring ◽  
Direct Interaction ◽  
X Ray Diffraction ◽  
One Pot ◽  
One Pot Synthesis ◽  
Ring Opening Reaction ◽  
Ring Opening Reactions ◽  
Intramolecular Cyclizations ◽  
The One

Introduction: The preparation of model 6-chloro-5-nitrothieno[2,3-c]pyridazines incorporating (2'-halo-5'-nitrophenyl) entity is described. Interaction of these substrates with N'-(aryl)benzothiohydrazides, in the presence of triethylamine, followed a formal [4+1] annulation, furnishing the respective 1,3,4-thiadiazoline–benzothiazolo [3,2-b]pyridazine hybrids directly. This one-pot synthesis implies thiophene ring-opening and two consecutive intramolecular cyclizations. The structures of the synthesized new hybrids are supported by MS, NMR, and IR spectral data and further confirmed by single-crystal X-ray diffraction. These hybrids exhibit antiproliferative activity with notable selectivity against solid tumor cell lines (IC50: 4-18 μM). Aims: This study aimed at exploring the scope and applicability of thiophene ring-opening reaction towards the synthesis of new thiadiazoline–[fused]tricyclic conjugates. Background: α-Chloro-β-nitrothienopyridazine underwent ring-opening upon reacting with N'-(aryl)benzothiohydrazides generating 1,3,4-thiadiazoline–benzothiazolo[3,2-b]pyridazines. Objective: This new thiophene ring-opening reaction is applied to the one-pot synthesis of thiadiazoline–benzothiazolo[3,2-b]pyridazine couples. Method: A direct interaction of α-chloro-β-nitrothienopyridazine with N'-(aryl)benzothiohydrazide at room temperature for 1-2 h occurred. Result: α-Chloro-β-nitrothieno[2,3-c]pyridazines are suitable substrates for the facile synthesis of thiadiazoline–benzothiazolo[3,2-b]pyridazine hybrids. Conclusion: This novel ring-opening reaction proceeds via formal [4+1] annulation and provides a versatile approach to various conjugated and/or fused five-membered heterocycles.

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