The Control of Photochromism of [3<i>H</i>]‑Naphthopyran Derivatives with Intramolecular CH−π Bonds

The photochromism of [3<i>H</i>]-naphthopyran derivatives can be switched from T-type to inverse- or P-type through the manipulation of relative thermodynamic stabilities of open isomers with intramolecular CH−π bonds

Access to l- and d-Iminosugar C-Glycosides from a d-<i>gluco</i>-Derived 6-Azidolactol Exploiting a Ring Isomerization/Alkylation Strategy

A flexible synthetic access to six-membered l- and d-iminosugar C-glycosides is reported starting from the easily available 6-azido-6-deoxy-2,3,4-tri-<i>O</i>-benzyl-d-glucopyranose precursor. This methodology involves a highly diastereoselective tandem ring enlargement/alkylation and a stereocontrolled ring contraction. It allows an efficient synthesis of iminosugar C-glycosides displaying structural diversity at both C-1 and C-6

The Control of Photochromism of [3<i>H</i>]‑Naphthopyran Derivatives with Intramolecular CH−π Bonds

The photochromism of [3<i>H</i>]-naphthopyran derivatives can be switched from T-type to inverse- or P-type through the manipulation of relative thermodynamic stabilities of open isomers with intramolecular CH−π bonds

Coordination of Lead(II) in the Supramolecular Environment Provided by a “Two-Story” Calix[6]arene-based N₆ Ligand

First insights into the coordination properties and host–guest behavior of a “two story” calix[6]­aza-cryptand (<b>1</b>) are described. The ligand is constituted of a triazacyclononane (TACN) cap and three pyridine (PY) spacers connected to the calix[6]­arene small rim. The resulting N₆ donor site coordinates Pb^II ions to give complexes that are highly stable. X-ray diffraction structures reveal a hemidirected environment for Pb^II with strong coordination to the TACN cap and weaker bonds with the three PY residues. A guest molecule, either water or EtOH, sitting in the calixarene macrocycle and hydrogen-bonded to the phenoxyl units at the level of the small rim further stabilizes the complexes through electrostatic interactions with the metal center and the calixarene core. In-depth ¹H NMR studies confirm the host–guest behavior of the complexes in solution, with evidence of embedment of neutral guest molecules such as EtOH, BuOH, and <i>N</i>-Me-formamide. Hence, in spite of the presence of a N₆ donor, the calixarene macrocycle can be open to guest interaction, giving rise to seven-coordinate dicationic complexes. Noteworthy also is the flexibility of the macrocycle that allows Pb^II to adopt its preferred hemidirected environment in spite of the three covalent links connecting the calixarene core to the three PY groups. The flexibility of the system is further illustrated by the possible coordination of an exogenous anionic ligand in the exo position. Hence, compared to the previously described “one story” calix[6]­aza-cryptands, ligand <b>1</b> displays several similar but also new features that are discussed

Asymmetric Synthesis of Fused Polycyclic Indazoles through Aminocatalyzed Aza-Michael Addition/Intramolecular Cyclization

The first example of an asymmetric aminocatalyzed aza-Michael addition of 1<i>H</i>-indazole derivatives to α,β-unsaturated aldehydes is described. The iminium/enamine cascade process lies at the heart of our strategy, leading to enantioenriched fused polycyclic indazole architectures. Variations on both the α,β-unsaturated aldehydes and the indazole-7-carbaldehyde heterocycles were studied in order to broaden the scope of the transformation in synthetically interesting directions. The fused polycyclic indazoles exhibit fluorescence properties and can undergo synthetic transformations

Dearomatization of Pyridines: Photochemical Skeletal Enlargement for the Synthesis of 1,2-Diazepines

In this report, we developed a unified and standardized one-pot sequence that converts pyridine derivatives into 1,2-diazepines by inserting a nitrogen atom. This skeletal transformation capitalizes on the in situ generation of 1-aminopyridinium ylides, which rearrange under UV light irradiation. A thorough evaluation of the key parameters (wavelength, reaction conditions, activating agent) allowed us to elaborate on a simple, mild, and user-friendly protocol. The model reaction was extrapolated to more than 40 examples, including drug derivatives, affording unique 7-membered structures. Mechanistic evidence supports the transient presence of a diazanorcaradiene species. Finally, pertinent transformations of the products, including ring contraction reactions to form pyrazoles, were conducted and paved the way to a broad application of the developed protocol

Coordination of Lead(II) in the Supramolecular Environment Provided by a “Two-Story” Calix[6]arene-based N₆ Ligand

First insights into the coordination properties and host–guest behavior of a “two story” calix[6]­aza-cryptand (<b>1</b>) are described. The ligand is constituted of a triazacyclononane (TACN) cap and three pyridine (PY) spacers connected to the calix[6]­arene small rim. The resulting N₆ donor site coordinates Pb^II ions to give complexes that are highly stable. X-ray diffraction structures reveal a hemidirected environment for Pb^II with strong coordination to the TACN cap and weaker bonds with the three PY residues. A guest molecule, either water or EtOH, sitting in the calixarene macrocycle and hydrogen-bonded to the phenoxyl units at the level of the small rim further stabilizes the complexes through electrostatic interactions with the metal center and the calixarene core. In-depth ¹H NMR studies confirm the host–guest behavior of the complexes in solution, with evidence of embedment of neutral guest molecules such as EtOH, BuOH, and <i>N</i>-Me-formamide. Hence, in spite of the presence of a N₆ donor, the calixarene macrocycle can be open to guest interaction, giving rise to seven-coordinate dicationic complexes. Noteworthy also is the flexibility of the macrocycle that allows Pb^II to adopt its preferred hemidirected environment in spite of the three covalent links connecting the calixarene core to the three PY groups. The flexibility of the system is further illustrated by the possible coordination of an exogenous anionic ligand in the exo position. Hence, compared to the previously described “one story” calix[6]­aza-cryptands, ligand <b>1</b> displays several similar but also new features that are discussed

<i>N</i>‑Arylazetidines: Preparation through Anionic Ring Closure

We report herein an efficient synthesis of diversely substituted <i>N</i>-aryl-2-cyanoazetidines based on an anionic ring-closure reaction. These compounds can be prepared from β-amino alcohols in enantiomerically pure form through a three-step sequence involving (i) copper-catalyzed <i>N</i>-arylation, (ii) <i>N</i>-cyanomethylation of the secondary aniline, and (iii) one-pot mesylation followed by ring closure induced by a base. This high-yielding sequence gives access to azetidines with a predictable and adjustable substitution pattern and also with predictable diastereoselectivity. These compounds are susceptible to multiple further derivatizations through Suzuki coupling or nitrile transformation, thus appearing as valuable new scaffolds for medicinal chemistry. Their rigid shape, featuring an almost planar <i>N</i>-arylamine and a planar four-membered ring, was revealed by both AM1 calculations and X-ray crystallography

Asymmetric Synthesis of Fused Polycyclic Indazoles through Aminocatalyzed Aza-Michael Addition/Intramolecular Cyclization

The first example of an asymmetric aminocatalyzed aza-Michael addition of 1<i>H</i>-indazole derivatives to α,β-unsaturated aldehydes is described. The iminium/enamine cascade process lies at the heart of our strategy, leading to enantioenriched fused polycyclic indazole architectures. Variations on both the α,β-unsaturated aldehydes and the indazole-7-carbaldehyde heterocycles were studied in order to broaden the scope of the transformation in synthetically interesting directions. The fused polycyclic indazoles exhibit fluorescence properties and can undergo synthetic transformations

HF-Induced Intramolecular <i>C</i>‑Arylation and <i>C</i>‑Alkylation/Fluorination of 2‑Aminoglycopyranoses

Internal <i>C</i>-aryl and <i>C</i>-alkyl glycosides derived from 2-aminoglycopyranoses have been synthesized, exploiting a HF-mediated stereoselective intramolecular glycosylation. These conditions are compatible with acetate protecting groups and allow introduction of aromatics with various electronic distributions at the anomeric position. This strategy also provides straightforward entry to original fluorinated sugar–azacycle hybrids via a tandem internal <i>C</i>-glycosylation/fluorination reaction starting from 2-<i>N</i>-allyl/propargyl glycopyranoses. All cyclizations proceed in a 1,2<i>-cis</i> stereocontrolled manner