Alkylidene Dihydropyridines As Synthetic Intermediates: Model Studies toward the Synthesis of the Bis(piperidine) Alkaloid Xestoproxamine C

Results of model studies demonstrating a stereoselective synthetic route to tricyclic analogues of the bis­(piperidine) alkaloid xestoproxamine C are presented. Dearomatization of a tricyclic pyridine derivative to afford an alkylidene dihydropyridine (anhydrobase) intermediate followed by catalytic heterogeneous hydrogenation was used to install the correct relative stereochemistry about the bis­(piperidine) ring system. Other key features of these model studies include development of an efficient ring-closing metathesis procedure to prepare macrocyclic derivatives of 3,4-disusbstituted pyridines, intramolecular cyclizations of alkylidene dihydropyridines to establish pyridine-substituted pyrrolidines and piperidines, successful homologation of pyridine-4-carboxaldehydes using formaldehyde dimethyl thioacetal monoxide (FAMSO), and application of B-alkyl Suzuki coupling to assemble substituted pyridines

Alkylidene Dihydropyridines As Synthetic Intermediates: Model Studies toward the Synthesis of the Bis(piperidine) Alkaloid Xestoproxamine C

Results of model studies demonstrating a stereoselective synthetic route to tricyclic analogues of the bis­(piperidine) alkaloid xestoproxamine C are presented. Dearomatization of a tricyclic pyridine derivative to afford an alkylidene dihydropyridine (anhydrobase) intermediate followed by catalytic heterogeneous hydrogenation was used to install the correct relative stereochemistry about the bis­(piperidine) ring system. Other key features of these model studies include development of an efficient ring-closing metathesis procedure to prepare macrocyclic derivatives of 3,4-disusbstituted pyridines, intramolecular cyclizations of alkylidene dihydropyridines to establish pyridine-substituted pyrrolidines and piperidines, successful homologation of pyridine-4-carboxaldehydes using formaldehyde dimethyl thioacetal monoxide (FAMSO), and application of B-alkyl Suzuki coupling to assemble substituted pyridines

Ligand Characterization of Covalently Functionalized Mesoporous Silica Nanoparticles: An NMR Toolbox Approach

Mesoporous silica materials are undergoing rapid development for numerous environmental and biomedical applications. These materials are commonly functionalized with small organic molecules through a reaction between an organosilane and the surface silanols. Despite widespread use and implementation of these materials, ligands on their surfaces are challenging to characterize, particularly in aqueous environments. Employing traditional physicochemical characterization methods such as adsorption isotherms, X-ray diffraction, and electron microscopy, as well as solution-phase ¹H NMR methods including one-dimensional NMR, diffusion ordered spectroscopy (DOSY) and two-dimensional nuclear Overhauser effect spectroscopy (NOESY), the labile nature of several different surface ligands on mesoporous silica nanoparticles is revealed. The data presented indicate a dynamic model of organosilane release from the surface, and adsorption of the released molecules is ultimately dependent on the nature of the binding of the functional group to the particle surface. A new paradigm for understanding chemical changes that take place at the liquid–solid interface is described, which incorporates a model of chemical dynamics in aqueous solution. Covalently functionalized nanomaterials are widely used, and the characterization of the ligands on their surfaces is of paramount importance, particularly when they are implemented in biomedical and environmental applications

Putting Cocrystal Stoichiometry to Work: A Reactive Hydrogen-Bonded “Superassembly” Enables Nanoscale Enlargement of a Metal–Organic Rhomboid via a Solid-State Photocycloaddition

Enlargement of a self-assembled metal organic rhomboid is achieved via the organic solid state. The solid-state synthesis of an elongated organic ligand was achieved by a template directed [2 + 2] photodimerization in a cocrystal. Initial cocrystals obtained of resorcinol template and reactant alkene afforded a 1:2 cocrystal with the alkene in a stacked yet photostable geometry. Cocrystallization performed in the presence of excess template resulted in a 3:2 cocrystal composed of novel discrete 10-component hydrogen-bonded “superassemblies” wherein the alkenes undergo a head-to head [2 + 2] photodimerization. Isolation and reaction of elongated photoproduct with Cu(II) ions afforded a metal-organic rhomboid of nanoscale dimensions that hosts small molecules in the solid state as guests

Intramolecular [2 + 2] Photodimerization Achieved in the Solid State via Coordination-Driven Self-Assembly

An intramolecular [2 + 2] photocycloaddition is achieved in the organic solid state via self-assembly of Ag­(I) ions and an <i>endo</i>-ditopic bipyridine. The cations aide to organize carbon–carbon double (CC) bonds attached to the bipyridine for the cycloaddition reaction. The CC bonds react regioselectively and quantitatively to afford a photoproduct with edge-sharing four-, five-, and six-membered rings. Our study demonstrates the first use of a metal–organic template to direct an intramolecular [2 + 2] photodimerization in the organic solid state

Putting Cocrystal Stoichiometry to Work: A Reactive Hydrogen-Bonded “Superassembly” Enables Nanoscale Enlargement of a Metal–Organic Rhomboid via a Solid-State Photocycloaddition

Enlargement of a self-assembled metal–organic rhomboid is achieved via the organic solid state. The solid-state synthesis of an elongated organic ligand was achieved by a template directed [2 + 2] photodimerization in a cocrystal. Initial cocrystals obtained of resorcinol template and reactant alkene afforded a 1:2 cocrystal with the alkene in a stacked yet photostable geometry. Cocrystallization performed in the presence of excess template resulted in a 3:2 cocrystal composed of novel discrete 10-component hydrogen-bonded “superassemblies” wherein the alkenes undergo a head-to-head [2 + 2] photodimerization. Isolation and reaction of elongated photoproduct with Cu­(II) ions afforded a metal–organic rhomboid of nanoscale dimensions that hosts small molecules in the solid state as guests

A solid-state [2 + 2] photodimerization involving coordination of Ag(I) ions to 2-pyridyl groups

<p>Photoreactive Ag(I) complexes of <i>p</i>-toluenesulfonate ions with the unsymmetrical alkene <i>trans</i>-1-(4-acetoxyphenyl)-2-(2-pyridyl)ethylene <b>1</b> is reported. The crystal [Ag(<i>p</i>-tol)(<b>1</b>)₂]•(H₂O) (<i>p</i>-tol = <i>p</i>-toluenesulfonate) undergoes a [2 + 2] photocycloaddition reaction in quantitative yield to afford the head-to-tail (ht) photoproduct <i>rctt</i>-1,3-bis(2-pyridyl)-2,4-bis(4-acetoxyphenyl)cyclobutane <b>2</b> regioselectively. The aromatic rings of the olefin participate in face-to-face π–π interactions and adopt an anti-conformation to position the carbon–carbon double bonds (C = C) in a suitable orientation to undergo photoreaction between neighboring complexes.</p