A highly diastereoselective (5+1) annulation of allenoates and pyrazolones catalyzed by CH3OK

The first (5+1) annulation of allenoates and pyrazolones catalyzed by CH3OK has been reported. A series of spiro-pyrazolone derivatives were obtained as single diastereomers in high yields (≤95%) under mild conditions. The synthetic utility was demonstrated by a scale-up reaction and various transformations of the products. The proposed mechanism suggests that the allenoate works as a 1,5-biselectrophilic 5C synthon for the first time and controlled experiments disclose that K+ plays an important role in the diastereoselectivity-determining step through an eight-membered ring transition state. Also, this 1,5-biselectrophilic allenoate will be able to act as a 5C synthon for (5+n) annulation.

Enantioselective Alkynylation of Pyrazole-4,5-diones with Terminal Alkynes Catalyzed by Copper/PyBisulidine

A copper/PyBisulidine-catalyzed enantioselective alkynylation of electrophilic pyrazole-4,5-dione with terminal alkynes has been developed. Chiral tertiary propargylic alcohols bearing the pyrazolone motif were prepared with yields (up to 99%) and enantioselectivities (up to 99% ee). The prominent feature of this protocol includes its mild reaction conditions and good stereoselectivities. The nonlinear effect study showed that the catalytically active specie was a monomeric catalyst and that the excess copper activated the alkynes through the π-system.

Access to Spiropyrazolone-butenolides through NHC-Catalyzed [3 + 2]-Asymmetric Annulation of 3-Bromoenals and 1H-Pyrazol-4,5-diones

The stereoselective synthesis of spirocyclic pyrazolin-5-ones by N-heterocyclic carbene (NHC) organocatalysis has been less studied so far. For this reason and considering the interest of this class of compounds, here, we present the NHC-catalyzed [3 + 2]-asymmetric annulation of β-bromoenals and 1H-pyrazol-4,5-diones that achieves to produce chiral spiropyrazolone-butenolides. The synthesis is general for aryl and heteroaryl β-bromo-α,β-unsaturated aldehydes and 1,3-disubstituted pyrazolones. The spirobutenolides have been obtained in good yields (up to 88%) and enantioselectivities (up to 97:3 er). This constitutes the first described example using pyrazoldiones as the starting materials for this class of spiro compounds.

Organocatalytic asymmetric synthesis of oxazolidino spiropyrazolinones via N,O-acetalization/aza Michael addition domino reaction between N-Boc pyrazolinone ketimines and γ-hydroxyenones

A squaramide-catalyzed asymmetric N,O-acetalization/aza Michael addition domino reaction between N-Boc ketimines derived from pyrazolin-5-ones and γ-hydroxyenones has been developed for the construction of pyrazolinone embedded spirooxazolidines. A hydroquinine derived bifunctional squaramide catalyst was found to be the most effective for this cascade spiroannulation. This new protocol allows the generation of two stereocenters and the desired products are obtained in good yields with moderate to good diastereoselectivities (up to 3.3 : 1 dr) and high enantioselectivities (up to >99% ee) from a range of substituted N-Boc pyrazolinone ketimines and γ-hydroxyenones. The developed protocol is amenable for a scale-up reaction.

Stereoselective N-Heterocyclic-Carbene-Catalyzed Formal [4 + 2] Cycloaddition: Access to Chiral Heterocyclic Cyclohexenones

The present study reports an asymmetric NHC-catalyzed formal [4 + 2] cycloaddition of heterocyclic alkenes containing a polarized double bond with an azolium-dienolate intermediate generated from α-bromo-α,β-unsaturated aldehydes without external oxidation of the Breslow intermediate. Heterocyclic cyclohexenones were produced in good isolated yields (typically about 90%) with good stereochemical outcomes (in most cases, dr > 20/1, and ee = 70-99%). The synthetic utility of the protocol was exemplified by the scope of heterocyclic alkenes.

A close look into the biological and synthetic aspects of fused pyrazole derivatives

The fusion of pyrazole scaffold with other skeletons creates a class of attractive molecules, demonstrating significant biological and chemical potentiality in the development of medicinal chemistry. Over the past few decades, numerous biologically active molecules featuring fused pyrazole moieties have been excavated and synthesized, some of which represented by sildenafil have been marketed as drugs, and the biological importance together with chemical synthesis strategies of fused pyrazole compounds, including structural modification based on lead compounds, have been steadily progressing. In this review, we focused our attention on the biological importance of fused pyrazoles and highlighted recent progress in the synthesis of this framework over the past 10 years. What' s more, the limitations, challenges, and future prospects were proposed, wishing to provide references for the development of pyrazole fused frameworks in the field of medicinal chemistry. Contents.

Copper-catalyzed asymmetric alkynylation of pyrazole-4,5-diones using chloramphenicol base-derived hydroxyl oxazoline ligands

The asymmetric copper-catalyzed alkynylation reactions of pyrazole 4,5-diones in the presence of hydroxyl oxazoline ligand, which was derived from low cost, easily accessible chloramphenicol base (ANP), were achieved. The notable...

NHC-catalysed [3 + 2]-asymmetric annulation between pyrazolin-4,5-diones and enals: synthesis of novel spirocyclic pyrazolone γ-butyrolactones and computational study of mechanism and stereoselectivity

Herein we present the first asymmetric synthesis of spiropyrazolone γ-butyrolactones from 1H-pyrazol-4,5-diones and enals by an NHC-catalysed [3 + 2] annulation. DFT calculations carried out predict the experimental configuration of final adducts.

Recent advances of N-heterocyclic carbenes in the applications of constructing carbo- and heterocyclic frameworks with potential biological activity

In recent years, N-heterocyclic carbenes (NHCs) have established themselves as a masterful and promising type of organocatalyst for the speedy construction of medicinally and biologically significant molecules from common and accessible small molecules. In particular, various cyclic scaffolds, including carbocycles and heterocycles, have been synthesized using NHCs via cycloaddition reaction. An exhaustive review focused on the chemistry of NHCs in these cyclic molecules has yet to be reported. In this contribution, a general picture of the utilization of NHCs in constructing twelve kinds of bioactive cyclic skeletons is firstly presented. We provide a systematic and comprehensive overview from the perspective of cycloaddition reactions; moreover, the limitations, challenges, and future prospects were discussed.

Stretchable chiral pockets for palladium-catalyzed highly chemo- and enantioselective allenylation

Pyrazolones are a vital class of heterocycles possessing various biological properties and much attention is paid to the diversified synthesis of enantiopure pyrazolone derivatives. We describe here the development of diphenylphosphinoalkanoic acid based chiral bisphosphine ligands, which are successfully applied to the palladium-catalyzed asymmetric allenylation of racemic pyrazol-5-ones. The reaction affords C-allenylation products, optically active pyrazol-5-ones bearing an allene unit, in high chemo- and enantioselectivity, with DACH-ZYC-Phos-C1 as the best ligand. The synthetic potential of the C-allenylation products is demonstrated. Furthermore, the enantioselectivity observed with DACH-ZYC-Phos-C1 is rationalized by density functional theory studies.

Chiral pyrazolone derivatives show promising biological activity in commercial drugs. Here, the authors report an enantioselective allenylation of pyrazolones by fine tuning of Trost’s ligands, which leads to a chiral pocket featuring high efficiency and asymmetric induction in the catalytic process.

Orthogonal Strapping of o-Haloaryl Ynones with Pyrazolones: A One-Pot, Domino Process toward Spiropyrazolones

A new class of spiroannulated pyrazolone scaffolds have been assembled from diverse o-haloaryl ynones and β-bromoalkenyl ynones via base mediated, one-pot, metal free, orthogonal strapping (tethering) mediated by the recursive anion(s) derived from pyrazolones. These convenient, preparatively useful transformations proceed through either a tandem Michael addition-intramolecular S_NAr reaction or a tandem Michael addition-intramolecular Ad_NE process to furnish a range of pharmacophoric, diverse, spiroannulated pyrazolones from readily accessible precursors.

Organo-catalyzed asymmetric cascade annulation reaction for the construction of bi-spirocyclic pyrazolone and oxindole derivatives

Organo-catalyzed tandem reaction between β,γ-unsaturated α-ketoesters and α-arylidene pyrazolinones was developed, and it provided chiral bi-spirocyclic pyrazolone and oxindole derivatives in high yields with good to excellent stereoselectivity.

Computational study on NHC catalyzed [4+2] annulation between γ-chloroenals and pyrazolinones: mechanism and stereoselectivity

Mechanisms and origins of stereoselectivity of NHC-catalyzed reaction between γ-chloroenal and α-arylidene pyrazolinone.

Rhodium-catalyzed regio- and enantioselective allylic alkylation of pyrazol-5-ones with alkynes

An atom-economical, regio- and enantioselective allylic alkylation of pyrazol-5-ones with alkynes was developed under rhodium catalysis.

Catalytic Asymmetric Synthesis of Spiropyrazolones and their Application in Medicinal Chemistry

Chiral spiropyrazolones are unique frameworks widely found in a large family of medicinally relevant compounds with various biological activities. Substantial research efforts have been invested toward stereoselectively by constructing spiro-cyclic structures. Over the past years, remarkable progress has been made in the organo- and metal-catalyzed asymmetric synthesis of spiropyrazolones through the utilization of accessible simple pyrazolone derivatives as raw materials. This review is organized according to the size of the spiro-ring fused at the 4-position of the pyrazolone framework. In the last part, the bio-evaluations of chiral spiropyrazolones for drug discovery are summarized.

A bifunctional pyrazolone–chromone synthon directed organocatalytic double Michael cascade reaction: forging five stereocenters in structurally diverse hexahydroxanthones

The merging of two or more known natural product-based scaffolds is a powerful and routine strategy to develop bioactive small molecules.

Organocatalytic asymmetric [4 + 1] annulation of in situ generated ortho-quinomethanes with 4-halo pyrazolones: straightforward access to chiral spiro-benzofuran pyrazolones

Asymmetric [4 + 1] annulation of ortho-quinomethanes with 4-halo pyrazolones was developed to construct spiro-benzofuran pyrazolones.

Asymmetric organocatalytic conjugated addition of pyrazolin-5-ones to ortho-quinomethanes: construction of vicinal tertiary and all-carbon quaternary stereocenters

An organocatalytic conjugated addition of pyrazolin-5-ones to ortho-quinomethanes was developed to construct the vicinal tertiary and all-carbon quaternary stereocenters.

Enantio- and diastereoselective synthesis of spiropyrazolones via an organocatalytic [1 + 2 + 3] multicomponent reaction

An asymmetric catalytic [1 + 2 + 3] multicomponent reaction of malononitrile, benzaldehyde and α-arylidene pyrazolinones to produce spiropyrazolones in high yields, with excellent enantioselectivities and good diastereoselectivities.

Pyrazolone: a powerful synthon for asymmetric diverse derivatizations

This feature article reports recent advances in the asymmetric diverse derivatizations of the pyrazolone scaffold.

Enantioselective aminocatalytic synthesis of tetrahydropyrano[2,3-c]pyrazoles via a domino Michael-hemiacetalization reaction with alkylidene pyrazolones

An enantioselective organocatalytic synthesis of fused tetrahydropyranopyrazole products has been achieved via a domino Michael-hemiacetalization reaction between alkylidene pyrazolones and cyclic ketones/pentanal.

Enantioselective organocatalytic Michael addition of isorhodanines to α,β-unsaturated aldehydes

The Michael reaction of substituted isorhodanines with α,β-unsaturated aldehydes in the presence of a catalytic amount of a chiral secondary amine is presented. This transformation proceeds in good to high yields furnishing the corresponding 4,5-disubstituted isorhodanine adducts in good to excellent enantioselectivities.