From simple quinoxalines to potent oxazolo[5,4-f]quinoxaline inhibitors of glycogen-synthase kinase 3 (GSK3)

2,7-Disubstituted oxazolo[5,4-f]quinoxalines were synthesized from 6-amino-2-chloroquinoxaline in four steps (iodination at C5, substitution of the chloro group, amidation and copper-catalysed cyclization) affording 28 to 44% overall yields. 2,8-Disubstituted oxazolo[5,4-f]quinoxaline was similarly obtained from 6-amino-3-chloroquinoxaline (39% overall yield). For the synthesis of other oxazolo[5,4-f]quinoxalines, amidation was rather performed before substitution; moreover, time-consuming purification steps were avoided between the amines and the final products (38 to 54% overall yields). Finally, a more efficient method involving merging of the last two steps in a sequential process was developed to access more derivatives (37 to 65% overall yields). Most of the oxazolo[5,4-f]quinoxalines were evaluated for their activity on a panel of protein kinases, and a few 2,8-disubstituted derivatives proved to inhibit GSK3 kinase. While experiments showed an ATP-competitive inhibition on GSK3β, structure-activity relationships allowed us to identify 2-(3-pyridyl)-8-(thiomorpholino)oxazolo[5,4-f]quinoxaline as the most potent inhibitor with an IC50 value of about 5 nM on GSK3α.

From ferrocene to fluorine-containing penta-substituted derivatives and all points in-between; or, how to increase the available chemical space

In spite of the growing interest in fluorine-containing compounds, and the improvements in materials, optical and biological properties that can arise from substitution of a phenyl ring by ferrocene within a molecular scaffold, synthetic strategies that allow the efficient preparation of fluoroferrocene derivatives are scarce. Following conversion of ferrocene to fluoroferrocene, we have developed routes to fluorine-containing di-, tri-, tetra- and penta-substituted ferrocene derivatives to extend the available chemical space. Our approach is based on the identification of suitable reagents and conditions to achieve fluorine-directed deprotometalation, and exploitation of the halogen 'dance' rearrangement in the ferrocene series.

Practical Chromatography-Free Synthesis of 2-Iodo-N,N-diiso­propylferrocenecarboxamide and Further Transformations

An efficient procedure able to deliver grams of racemic and enantioenriched 2-iodo-N,N-diisopropylferrocenecarboxamide without chromatographic purification was developed. To introduce the halogen, two procedures, one using the nBuLi-TMEDA chelate and one using a lithium amide in the presence of ZnCl2 as in situ trap were developed. Further functionalization by Suzuki–Miyaura and Ullman-type cross-couplings was investigated to access a variety of ferrocene derivatives.

Asymmetric synthesis of hetero-1,2,3,4,5-pentasubstituted ferrocenes

The first synthesis of enantioenriched ferrocenes bearing five different substituents on the same cyclopentadienyl ring is described through an unprecedented asymmetric halogen 'dance' reaction. This work not only extends the chemistry of fluoroferrocene derivatives and constitutes the very first entry into the world of enantioenriched hetero-pentasubstituted ferrocenes, it also lays the foundation for research in other metallocene families.

Enantioselective deprotometalation of N,N-dialkyl ferrocenecarboxamides using metal amides

Our attempts to deprotometalate N,N-dialkyl ferrocenecarboxamides enantioselectively by using chiral lithium or lithium–zinc dialkylamides are reported.

Twofold Ferrocene C–H Lithiations For One-Step Difunctionalizations

For some aromatics, a twofold C–H deprotolithiation can be achieved, allowing these compounds to be subsequently difunctionalized in one step. This short review brings together examples in which ferrocenes are converted in this way.

1 Introduction

2 Bare Ferrocene

3 Ferrocenes Substituted by Alkyl or Silyl Groups

4 Ferrocenes Substituted by Aminoalkyls

5 Ferrocenes Substituted by Halogens or Oxygen-Based Groups

6 Ferrocenes Substituted by Alkoxyalkyls or Acetals

7 Ferrocenes Substituted by Sulfoxides

8 Ferrocenes Substituted by Oxazolines

9 Ferrocenes Substituted by Carboxamides

10 Conclusion

Deprotonative Metalation of Methoxy-Substituted Arenes Using Lithium 2,2,6,6-Tetramethylpiperidide: Experimental and Computational Study

The reaction pathways of lithium 2,2,6,6-tetramethylpiperidide (LiTMP)-mediated deprotonative metalation of methoxy-substituted arenes were investigated. Importantly, it was experimentally observed that, whereas TMEDA has no effect on the course of the reactions, the presence of more than the stoichiometric amount of LiCl is deleterious, in particular without an in situ trap. These effects were corroborated by the DFT calculations. The reaction mechanisms, such as the structure of the active species in the deprotonation event, the reaction pathways by each postulated LiTMP complex, the stabilization effects by in situ trapping using zinc species, and some kinetic interpretation, are discussed herein.

In Situ ‘Trans-Metal Trapping’: An Efficient Way to Extend the Scope of Aromatic Deprotometalation

Deprotometalation is an efficient method to functionalize regioselectively aromatic compounds including heterocycles. This short review shows how it is possible to intercept aryllithiums (and other polar arylmetals) as soon as they are formed by in situ ‘trans-metal trapping’. The approach avoids long contact between aryllithiums and sensitive substrates. In addition, it allows less activated substrates to be deprotonated by non-nucleophilic lithium amides. While using chloro­silanes and borates still arouses the interest of chemists, more recently, methods based on zinc, aluminum and gallium have appeared, enabling this chemistry to grow dramatically.

1 Introduction

2 Silicon-Based In Situ Traps

3 Boron-Based In Situ Traps

4 Zinc-Based In Situ Traps

5 Aluminum- and Gallium-Based In Situ Traps

6 Other In Situ Traps

7 Continuous-Flow In Situ ‘Trans-Metal Trapping’

8 Conclusion

Application of the Curtius rearrangement to the synthesis of 1′-aminoferrocene-1-carboxylic acid derivatives

The shortest synthesis of N-protected 1′-aminoferrocene-1-carboxylic acid from readily available ferrocene-1,1′-dicarboxylic acid is reported.

Ferrocenecarboxylic anhydride: identification of a new polymorph

A new monoclinic polymorph of ferrocenecarboxylic anhydride, [Fe₂(C₅H₅)₂(C₁₂H₈O₃)], was obtained. Three molecules are present in the asymmetric unit, two of them being nearly identical (r.m.s. deviation = 0.11 Å), with the Fe atoms on the same side of the anhydride functional group. In the third molecule, the two Fe atoms are located at opposite sides of the functional group (ferrocene-ferrocene pseudo-torsion angle = 146.2°), a very unsual feature in metallocene anhydrides. A network of weak intermolecular hydrogen bonds was also disclosed.

Interactions of cyclodextrins and their derivatives with toxic organophosphorus compounds

The aim of this review is to provide an update on the current use of cyclodextrins against organophosphorus compound intoxications. Organophosphorus pesticides and nerve agents play a determinant role in the inhibition of cholinesterases. The cyclic structure of cyclodextrins and their toroidal shape are perfectly suitable to design new chemical scavengers able to trap and hydrolyze the organophosphorus compounds before they reach their biological target.

Synthesis of ferrocene amides and esters from aminoferrocene and 2-substituted ferrocenecarboxylic acid and properties thereof

The X-ray diffraction structure of the ferrocene ester FcE-1 showed the presence of an intermolecular hydrogen bond between the amide functional groups.

Functionalization of pyridyl ketones using deprotolithiation-in situ zincation

Metallation of aryl ketones was achieved by using LiTMP in the presence of ZnCl₂·TMEDA, as evidenced by subsequent interception with iodine or by palladium-catalysed cross-coupling reaction.

Catalytic chemical amide synthesis at room temperature: one more step toward peptide synthesis

An efficient method has been developed for direct amide bond synthesis between carboxylic acids and amines via (2-(thiophen-2-ylmethyl)phenyl)boronic acid as a highly active bench-stable catalyst. This catalyst was found to be very effective at room temperature for a large range of substrates with slightly higher temperatures required for challenging ones. This methodology can be applied to aliphatic, α-hydroxyl, aromatic, and heteroaromatic acids as well as primary, secondary, heterocyclic, and even functionalized amines. Notably, N-Boc-protected amino acids were successfully coupled in good yields with very little racemization. An example of catalytic dipeptide synthesis is reported.

Synthesis of prostaglandin analogues, latanoprost and bimatoprost, using organocatalysis via a key bicyclic enal intermediate

Two antiglaucoma drugs, bimatoprost and latanoprost, which are analogues of the prostaglandin, PGF2α, have been synthesized in just 7 and 8 steps, respectively. The syntheses employ an organocatalytic aldol reaction that converts succinaldehyde into a key bicyclic enal intermediate, which is primed for attachment of the required lower and upper side chains. By utilizing the crystalline lactone, the drug molecules were prepared in >99% ee.

Enantioselective synthesis of putative lipiarmycin aglycon related to fidaxomicin/tiacumicin B

An enantioselective synthesis of a putative lipiarmycin aglycon was accomplished and features: 1) Brown's enantioselective alkoxyallylboration and allylation of aldehydes, 2) chain elongation by iterative Horner-Wadsworth-Emmons olefination, 3) Evans' aldol reaction and 4) an ene-diene ring-closing metathesis. A neighboring-group-assisted chemoselective reductive desilylation was uncovered in this study and was instrumental to the realization of the present synthesis.