Bifunctional Ligands: Evaluating the Role of Acidic Protons in the Secondary Coordination Sphere.

To evaluate bifunctional ligand reactivity involving NH acidic sites in the secondary coordination sphere, complexes where the proton has been substituted with a methyl group (NMe) are often investigated. An alternative strategy involves substitution of the NH group for an O. This contribution considers and compares the merits of these approaches; the synthesis and characterization of cationic square-planar Rh carbonyl complexes bearing diprotic bispyrazole pyridine ligand L1, and the bis-methylated pyrazole pyridine ligand L1Me are described.

Discovery of an Azabicyclo[2.1.1]hexane Piperazinium Salt and Its Application in Medicinal Chemistry via a Rearrangement.

Herein we report the discovery of an azabicyclo[2.1.1]hexane piperazinium methanesulfonate salt from an unexpected rearrangement reaction in the preparation of ligand-directed degraders (LDDs).

Bushy-Tailed QACs: The Development of Multicationic Quaternary Ammonium Compounds with a High Degree of Alkyl Chain Substitution.

Quaternary ammonium compounds have served as a first line of protection for human health as surface disinfectants and sanitizers for nearly a century. However, increasing levels of bacterial resistance have spurred the development of novel QAC architectures. In light of the observed reduction in eukaryotic cell toxicity when the alkyl chains on QACs are shorter in nature (≤10 C), we prepared 47 QAC architectures that bear multiple short alkyl chains appended to up to three cationic groups, thus rendering them "bushy-tailed" multiQACs.

Metallacyclobuta-(2,3)-diene: A Bidentate Ligand for Stream-line Synthesis of First Row Transition Metal Catalysts for Cyclic Polymerization of Phenylacetylene.

Described here is a direct entry to two examples of 3d transition metal catalysts that are active for the cyclic polymerization of phenylacetylene, namely, [(BDI)M{κ -C,C-(Me SiC SiMe )}] (2-M) (BDI=[ArNC(CH )] CH , Ar=2,6- Pr C H ; M=Ti, V). Catalysts are prepared in one step by the treatment of [(BDI)MCl ] (1-M, M=Ti, V) with 1,3-dilithioallene [Li (Me SiC SiMe )]. Complexes 2-M have been spectroscopically and structurally characterized and the polymers that are catalytically formed from phenylacetylene were verified to have a cyclic topology based on a combination of size-exclusion chromatography (SEC) and intrinsic viscosity studies.

Heterocycles via SiCl-Promoted Isocyanide Additions to Oxonitriles.

SiCl promotes isocyanide additions to oxoalkenenitriles to selectively generate 3-acylpyrroles, 2-aminofurans, or pyrrolidinones. Cyclic oxoalkenenitriles add 2 equiv of an isocyanide that installs the two core atoms of an acylpyrrole and a nitrile substituent, whereas acyclic oxoalkenenitriles add 1 equiv of an isocyanide to afford 2-aminofurans; subsequent air oxidation generates pyrrolidinones via a furan oxygenation-cleavage-cyclization sequence. The syntheses proceed under mild conditions to rapidly access three richly decorated heterocycles.

1-Ethyl-4-isopropyl-1,2,4-triazolium bromide.

An ionic compound consisting of a triazolium cation and bromide anion, CHN ·Br, has been synthesized and structurally characterized using single-crystal X-ray diffraction and NMR. The compound crystallizes in the monoclinic space group 2/ with the non-hydrogen atoms of one cation lying on general positions and the others lying on a mirror plane. One bromide ion also lies on the mirror.

A mononuclear, terminal titanium(III) imido.

We report the first mononuclear Ti complex possessing a terminal imido ligand. Complex [TpTi{NSi(CH)}(THF)] (2) (Tp = hydridotris(3--butyl-5-methylpyrazol-1-yl)borate) is prepared by reduction of [TpTi{NSi(CH)}(Cl)] (1) with KC in high yield. The connectivity and metalloradical nature of 2 were confirmed by single crystal X-ray diffraction studies, Q- and X-band EPR, UV-Vis and H NMR spectroscopies.

Polar-Radical Cyclization Cascades with Magnesiated Nitriles.

Naphthalene converts magnesiated ω-alkenylnitriles into bi- and tricyclic ketones via a polar-radical addition-cyclization cascade. One-electron oxidation of magnesiated nitriles generates nitrile-stabilized radicals that cyclize onto a pendant olefin and then rebound onto the nitrile through a reduction-cyclization sequence; subsequent hydrolysis affords a diverse array of bicyclo[3.2.

Soft QPCs: Biscationic Quaternary Phosphonium Compounds as Soft Antimicrobial Agents.

Quaternary ammonium compounds (QACs) serve as a first line of defense against infectious pathogens. As resistance to QACs emerges in the environment, the development of next-generation disinfectants is of utmost priority for human health. Balancing antibacterial potency with environmental considerations is required to effectively counter the development of bacterial resistance.

One-Pot Syntheses of Substituted Oxazoles and Imidazoles from the Isocyanide Asmic.

Substituted oxazoles and imidazoles are synthesized in one pot from the isocyanide building block Asmic (anisylsulfanylmethyl isocyanide), an alkyl halide, and an acid chloride or nitrile, respectively. The modular assembly employs sequential deprotonation-alkylation and deprotonation-acylation or imination of Asmic, followed by an unusual carbon-sulfur bond cleavage to construct the azole. The strategy is robust, highly efficient, and affords C4-C5 disubstituted oxazoles or imidazoles in a single operation.

Oxidative DMSO Cyclization Cascade to Bicyclic Hydroxyketonitriles.

Thermolysis of ω-iodoalkyl-β-siloxyalkenenitriles in DMSO triggers an oxidative cyclization cascade that affords highly oxygenated hydrindanones, decalones, and undecanones. The cyclization cascade is highly unusual on three counts: the cyclization installs a contiguous array of tertiary-quaternary-tertiary centers, thermolysis equilibrates a quaternary center, and the enolsilyl ether crossed-aldol proceeds without a catalyst.

Metal-Binding Q-Proline Macrocycles.

We introduce the efficient Fmoc-SPPS and peptoid synthesis of Q-proline-based, metal-binding macrocycles (QPMs), which bind metal cations and display nine functional groups. Metal-free QPMs are disordered, evidenced by NMR and a crystal structure of QPM- obtained through racemic crystallization. Upon addition of metal cations, QPMs adopt ordered structures.

Asmic Isocyanide [3 + 2] Cascade to Dihydrooxazoles and Dihydroimidazoles.

The versatile isocyanide building block Asmic, anisylsulfanylmethylisocyanide, reacts with aldehydes and ketones in a BF·OEt-mediated condensation to afford thioimidoyl-substituted 2,5-dihydrooxazoles. The condensation is distinguished from related base and transition-metal-catalyzed [3 + 2] processes in proceeding via the condensation of aldehydes and ketones with 2 equiv of an isocyanide followed by a molecular rearrangement that installs four new bonds. BF·OEt mediates an analogous condensation of Asmic with imines to generate -substituted dihydroimidazoles.