Mechanistic insight into cobalt-mediated [2 + 2 + 2]-cycloaddition reactions with γ-alkylidenebutenolide and γ-alkylidenebuterolactam as 2π partners.

The molecular complexity of recently reported cobalt(III) polycyclic complexes, resulting from an intramolecular formal (2 + 2 + 3) cycloaddition reaction on an enediyne containing a lactone moiety, has prompted us to computationally review the mechanisms of cobalt cycloaddition reactions with γ-alkylidenebutenolide or γ-alkylidenebuterolactam as 2π partners. Computed mechanisms are compared, leading to either cobalt(III)- or cobalt(I)-spiro complexes depending of both the nature of the reaction (intra- intermolecular pathway) and the nature of the 2π partner (γ-alkylidenebutenolide γ-alkylidenebuterolactam). These proposed mechanisms are supported by experiments, allowing us to report the synthesis and characterization of the predicted compounds.

Stereoselective formation of boron-stereogenic organoboron derivatives.

Four-coordinate organoboron derivatives present interesting chemical, physical, biological, electronical, and optical properties. Given the increasing demand for the synthesis of smart functional materials based on chiral organoboron compounds, the exploration of stereoselective synthesis of boron-stereogenic organo-derivatives is highly desirable. However, the stereoselective construction of organoboron compounds stereogenic at boron has been far less studied than other elements of the main group due to configurational stability concerns.

Enantioselective Construction of Tetrasubstituted Carbon Stereocenters via Chiral Phosphoric Acid-Catalyzed Friedel-Craft Alkylation of Indoles with 5-Substituted Hydroxybutyrolactams.

The first intermolecular organocatalytic enantioselective addition of indoles to prochiral 5-membered cyclic -acyliminium ions, generated from 5-hydroxy-α,β-unsaturated pyrrolidin-2-ones, is reported hereinafter. The reaction proceeds smoothly with a range of 5-hydroxy-5-substituted-α,β-unsaturated pyrrolidin-2-ones and indoles using BINOL-derived phosphoric acid catalyst to afford α,β-unsaturated lactams embedding a tetrasubstituted stereogenic center in high yields and enantioselectivities.

Synthesis and Electron Accepting Properties of Two Di(benz[]indenone)-Fused Tetraazaanthracene Isomers.

We designed and synthesized a novel di(benz[]indenone)-fused tetraazaanthracene derivative and isolated its two isomers, and , having and configurations, respectively. Their structure and that of the condensation reaction intermediates, - and -, were fully characterized using one- and two-dimensional nuclear magnetic resonance spectroscopy and single-crystal X-ray diffraction. The optical and electronic properties of and were investigated using ultraviolet-visible absorption and fluorescence spectroscopies, cyclic voltammetry, and time-dependent density functional theory calculations.

Impact of the Difluoromethylene Group in the Organocatalyzed Acylative Kinetic Resolution of α,α-Difluorohydrins.

Due to the omnipresence of chiral organofluorine compounds in pharmaceutical, agrochemical, and material chemistry, the development of enantioselective methods for their preparation is highly desirable. In the present study, the enantioselective organocatalyzed acylation of α,α-difluorohydrins using a commercially available chiral isothiourea is reported through a kinetic resolution (KR) process. It reveals that the difluoromethylene moiety (C(sp )F ) can serve as a directing group through electrostatic fluorine-cation interactions, greatly improving the enantioselectivity of the KR.

Small rings in the bigger picture: ring expansion of three- and four-membered rings to access larger all-carbon cyclic systems.

The release of the inherent ring strain of cyclobutane and cyclopropane derivatives allows a rapid build-up of molecular complexity. This review highlights the state-of-the-art of the ring expansions of three- and four-membered cycles and is organised by types of reactions with emphasis on the reaction mechanisms. Selected examples are discussed to illustrate the synthetic potential of this elegant synthetic tool.

Access to Fluorenones Using Benzocyclopentynone Surrogate as Partner for the [2 + 2 + 2] Cycloaddition Reaction.

A convenient and versatile procedure for the straightforward synthesis of substituted fluorenones as valuable scaffolds is described under rhodium catalysis. The present [2 + 2 + 2] cycloaddition reaction of diynes with 3-acetoxy or-3-alkoxyindenones as surrogates of the highly reactive benzocyclopentynone 2π partner allows the preparation of various fluorenone-type derivatives in good yields and provides an additional and tunable process for the generation of more challenging molecules with application in pharmaceutical, polymer, and material sciences.

Investigation of the rhodium-catalyzed hydroboration of NHC-boranes: the role of alkene coordination and the origin of enantioselectivity.

The mechanism of the intramolecular enantioselective rhodium(i)-catalyzed hydroboration of NHC-boranes is investigated by experimental reactivity measurements and molecular electronic structure calculations, within the framework of the Density Functional Theory and the Random Phase Approximation methods. The crucial role of alkene coordination and the origin of enantioselectivity are discussed. Two possible mechanisms are considered, via either prior hydride migratory insertion or boron migratory insertion.

When cobalt-mediated [2 + 2 + 2] cycloaddition reaction dares go astray: synthesis of unprecedented cobalt(iii)-complexes.

In sharp contrast with the standard [2 + 2 + 2] cycloaddition reaction of diyne/ene, cobalt-mediated cycloadditions with γ-alkylidenebutenolide led to unprecedented cobalt(iii) polycyclic complexes. A plausible mechanism supported by a computational study based on an unusual fragmentation of the butenolide moiety was postulated to account for this original reaction.

Strategic Stereoselective Halogen (F, Cl) Insertion: A Tool to Enhance Supramolecular Properties in Polyols.

To improve the supramolecular properties of organic compounds, chemists continuously need to identify new tools. Herein, the influence of the stereoselective insertion of halogen atoms (F or Cl) on different supramolecular properties is analyzed. Inserting anti-halohydrins in polyols considerably strengthens the H-bonding networks and other supramolecular interactions.

Highly diastereoselective preparation of chiral NHC-boranes stereogenic at the boron atom.

Stereogenic main group elements are clearly generating interest in the enantioselective catalysis field. Surprisingly, while chiral organoboron reagents are very useful in stereoselective transformations, few scaffolds stereogenic at boron and configurationally stable have been reported to date. Herein, we describe an original library of chiral NHC-boranes, stereogenic at the boron atom, that has been prepared in only a few steps and in good yields (up to 93%).

Spatially resolved acyl transfer on surface by organo-catalytic scanning probe nanolithography (o-cSPL).

Groundbreaking research done in the area of nanolithography makes it a versatile tool to produce nanopatterns for a broad range of chemical surface functionalization or physical modifications. We report for the first time an organocatalytic scanning probe nanolithography (o-cSPL) approach. Covalent binding of an organocatalyst on the apex of an atomic force microscope (AFM) tip gives way to a system that allows the formation of locally defined acylated-alcohol patterns on self-assembled monolayers (SAMs).

Double Catalytic Kinetic Resolution (DoCKR) of Acyclic anti-1,3-Diols: The Additive Horeau Amplification.

The concept of a synergistic double catalytic kinetic resolution (DoCKR) as described in this article was successfully applied to racemic acyclic anti-1,3-diols, a common motif in natural products. This process takes advantage of an additive Horeau amplification involving two successive enantioselective organocatalytic acylation reactions, and leads to diesters and recovered diols with high enantiopurities. It was first developed with C -symmetrical diols and then further extended to non-C -symmetrical anti diols to prepare useful chiral building blocks.

Reply to the 'Comment on "trans-1,2-Disiloxybenzocyclobutene, an adequate partner for the auto-oxidation: EPR/spin trapping and theoretical studies"' by H.-G. Korth, P. Mulder and T. Paul, Phys. Chem. Chem. Phys., 2017, 19, C6CP04187F.

The proposal and the comments made by Korth et al. on a biradical intermediate along the isomerization path of the reaction of trans-1,2-tert-butyldimethyldisilyloxybenzocyclobutene 1 with dioxygen are unsuitable in our case. The mechanism scenario that we proposed is in agreement with our experimental observations.

Straightforward and Controlled Shape Access to Efficient Macrocyclic Imidazolylboronium Anion Receptors.

A straightforward synthesis of air- and water-stable bis-cationic macrocyclic imidazolylboronium anion receptors is described herein. By taking advantage of the bulky and rigid 9-borabicyclo[3.3.

Catalytic Scanning Probe Nanolithography (cSPL): Control of the AFM Parameters in Order to Achieve Sub-100-nm Spatially Resolved Epoxidation of Alkenes Grafted onto a Surface.

Scanning probe lithography (SPL) appears to be a reliable alternative to the use of masks in traditional lithography techniques as it offers the possibility of directly producing specific chemical functionalities with nanoscale spatial control. We have recently extend the range of applications of catalytic SPL (cSPL) by introducing a homogeneous catalyst immobilized on the apex of a scanning probe. Here we investigate the importance of atomic force microscopy (AFM) physical parameters (applied force, writing speed, and interline distance) on the resultant chemical activity in this cSPL methodology through the direct topographic observation of nanostructured surfaces.

Highly Enantioselective Acylation of Acyclic Meso 1,3-Diols through Synergistic Isothiourea-Catalyzed Desymmetrization/Chiroablative Kinetic Resolution.

A general and highly efficient organocatalyzed desymmetrization of acyclic meso 1,3-diols through acyl transfer using chiral isothioureas is described. The introduction of π-systems in the acyclic substrates provided new opportunities in terms of reactivity, enantioselectivity and synthetic potential. To reach this high level of enantioselectivity (up to er >99:1), the reaction proceeds through a synergistic mechanism involving a desymmetrization reaction and a chiroablative kinetic resolution process.

Synthesis and structure of Ag(I), Pd(II), Rh(I), Ru(II) and Au(I) NHC-complexes with a pendant Lewis acidic boronic ester moiety.

Bifunctional Ag(I), Pd(II), Rh(I), Ru(II) and Au(I) complexes containing a NHC ligand and a pendant trivalent boron moiety have been synthesized in high yields. Fine-tuned reaction conditions were used to prevent potential ligand self-quenching or polymerization due to the eventual co-existence in situ of free NHC (Lewis base) and boronic ester (Lewis acid) in the same molecule.

trans-1,2-Disiloxybenzocyclobutene, an adequate partner for the auto-oxidation: EPR/spin trapping and theoretical studies.

The auto-oxidation of trans-1,2-disiloxybenzocyclobutene was found to be very efficient, giving endo-peroxide in quantitative yield. Each step of the mechanism of spin-forbidden addition of triplet oxygen O2((3)Σg) was studied by both EPR/spin trapping and theoretical studies.

Directed studies towards the total synthesis of (+)-13-deoxytedanolide: simple and convenient synthesis of the C8-C16 fragment.

A straightforward synthesis of the enantioenriched C8-C16 south part of (+)-13-deoxytedanolide has been reported. The strength of this approach relies on the preparation of similar functionalized fragments via the transformation of a unique dihydrofuran building block through a 1,2-metallate rearrangement.

First studies directed towards the diastereoselective synthesis of the BCD tricyclic core of brownin F.

The BCD tricyclic core of brownin F was prepared in eight synthetic operations for the first time. Our synthesis features a diastereo-, chemo- and regioselective intramolecular [3 + 2] cycloaddition between a cyclic carbonyl ylide and a γ-alkylidenebutenolide.

3-Bromopenta-2,4-dienylsilane: a useful reagent for the preparation of [3]dendralenes and polycyclic compounds.

Starting from (Z)-1-trimethylsilyl-3-bromopenta-2,4-diene, a lithium-bromine exchange reaction followed by addition onto carbonyl compounds provided the corresponding dienyl alcohols. A Peterson-type γ-elimination promoted by a catalytic amount of trimethylsilyl triflate cross-conjugated gave triene systems ([3]dendralene) which rapidly reacted with the appropriate dienophiles to yield tandem intermolecular Diels-Alder cycloadducts.

Diastereoselective access to polyoxygenated polycyclic spirolactones through a rhodium-catalyzed [3+2] cycloaddition reaction: experimental and theoretical studies.

The synthetic utility of γ-alkylidenebutenolides is demonstrated as highly competent dipolarophile partners in both intra- and intermolecular rhodium(II)-catalyzed 1,3-dipolar cycloaddition reactions. The strength of this approach lies in the formation of spiro[6,4]lactone moieties with the concomitant construction of quaternary spiro stereocenters. Typically, the construction of spirolactones involves an esterification step, which has often been reported as a "biosynthetic pathway", and often occurs either as or near to the final step of a total synthesis.

Asymmetric rhodium-directed anti-Markovnikov regioselective boracyclopentannulation.

A Shimoi-type activation of B-H bond of NHC-boranes by a diphosphane-ligated cationic Rh complex was applied in an unprecedented intramolecular hydroboration reaction of simple olefins. The use of NHC-boranes as hydroborating reagents is still undisclosed due to their nonreactivity toward alkenes which could be explained by the high stability of this complex rendering it unable to provide a "free" borane hydroborating reagent. B-H bond Rh activation of NHC-borane circumvents this limitation, and asymmetric Rh-directed anti-Markovnikov boracyclopentannulation reaction led to a library of enantioenriched cyclic boranes in high yield (up to 94%) with high regio- (up to 100%) and enantioselectivity (er up to 99.

Dramatic influence of the substitution of alkylidene-5H-furan-2-ones in Diels-Alder cycloadditions with o-quinonedimethide as diene partner: en route to the CDEF polycyclic ring system of lactonamycin.

An efficient and rapid synthesis of the CDEF ring system of lactonamycinone is reported via a highly chemo- and diastereoselective intermolecular Diels-Alder cycloaddition between trans-1,2-disilyloxybenzocyclobutene and the appropriate γ-alkylidenebutenolide. The feasibility and the total chemoselectivity of the [4 + 2] cycloaddition for the construction of a spirolactone moiety via an intramolecular approach (IMDA) using both partners is also described demonstrating the versatility of the γ-alkylidenebutenolide building block.