Dinuclear Cobalt(II) Bis-Dipyrromethane Complexes: Synthesis via Divergent Transmetalation Reactions.

A bis-dipyrromethane ligand, 4,4'-bis(1,1-bis(3,5-dimethyl-1H-pyrrol-2-yl)ethyl)-1,1'-biphenyl, [H-BDPM-BPh] (), is synthesized via acid-catalyzed electrophilic aromatic substitution of 2,4-dimethylpyrrole with 4,4'-diacetylbiphenyl. Subsequent deprotonation of with -BuLi yields the corresponding Li-salt [Li-BDPM-BPh] (). Transmetalation involving and either CoCl or [Co(HMDS)] (HMDS = -N(Si(CH))) results in dinuclear Co(II) complexes.

Chloroformate-mediated ring cleavage of indole alkaloids leads to re-engineered antiplasmodial agents.

Natural product ring distortion strategies have enabled rapid access to unique libraries of stereochemically complex compounds to explore new chemical space and increase our understanding of biological processes related to human disease. Herein is described the development of a ring-cleavage strategy using the indole alkaloids yohimbine, apovincamine, vinburnine, and reserpine that were reacted with a diversity of chloroformates paired with various alcohol/thiol nucleophiles to enable the rapid synthesis of 47 novel small molecules. Ring cleavage reactions of yohimbine and reserpine produced two diastereomeric products in moderate to excellent yields, whereas apovincamine and vinburnine produced a single diastereomeric product in significantly lower yields.

Tethered Alkylidenes for REMP from Carbon Disulfide Cleavage.

Reactions between tungsten alkylidyne [BuOCO]W≡CBu(THF) and sulfur containing small molecules are reported. Complex reacts with CS to produce intermediate η bound CS complex [OC(BuC═)W(η-(,)-CS)(THF)] . Heating complex provides a mixture of a monomeric tungsten sulfido complex and a dimeric complex in a 4:1 ratio, respectively.

Computation-guided scaffold exploration of 2,6-1,10-eunicellanes.

Eunicellane diterpenoids are a unique family of natural products containing a foundational 6/10-bicyclic framework and can be divided into two main classes, and , based on the configurations of their ring fusion at C1 and C10. Previous studies on two bacterial diterpene synthases, Bnd4 and AlbS, revealed that these enzymes form - and -eunicellane skeletons, respectively. Although the structures of these diterpenes only differed in their configuration at a single position, C1, they displayed distinct chemical and thermal reactivities.

Structure-property relationships in dicyanopyrazinoquinoxalines and their hydrogen-bonding-capable dihydropyrazinoquinoxalinedione derivatives.

Presented here is the design, synthesis, and study of a variety of novel hydrogen-bonding-capable π-conjugated -heteroacenes, 1,4-dihydropyrazino[2,3-]quinoxaline-2,3-diones (DPQDs). The DPQDs were accessed from the corresponding weakly hydrogen-bonding dicyanopyrazinoquinoxaline (DCPQ) suspensions with excess potassium hydroxide, resulting in moderate to good yields. Both families of compounds were analyzed by UV-vis and NMR spectroscopy, where the consequences of hydrogen bonding capability could be assessed through the structure-property studies.

Dicyanorhodanine-Pyrrole Conjugates for Visible Light-Driven Quantitative Photoswitching in Solution and the Solid State.

Small molecule photoswitches capable of toggling between two distinct molecular states in response to light are versatile tools to monitor biological processes, control photochemistry, and design smart materials. In this work, six novel dicyanorhodanine-based pyrrole-containing photoswitches are reported. The molecular design avails both the and isomers from synthesis, where each can be isolated using chromatographic techniques.

Catalytic Enantioselective [4+2] Cycloadditions of Salicylaldehyde Acetals with Enol Ethers.

A readily accessible conjugate-base-stabilized carboxylic acid (CBSCA) catalyst facilitates highly enantioselective [4+2] cycloaddition reactions of salicylaldehyde-derived acetals and cyclic enol ethers, resulting in the formation of polycyclic chromanes with oxygenation in the 2- and 4-positions. Stereochemically more complex products can be obtained from racemic enol ethers. Spirocyclic products are also accessible.

Alicyclic-Amine-Derived Imine-BF Complexes: Easy-to-Make Building Blocks for the Synthesis of Valuable α-Functionalized Azacycles.

A new strategy to access α-functionalized alicyclic amines via their corresponding imine-BF complexes is reported. Isolable imine-BF complexes, readily prepared via dehydrohalogenation of N-bromoamines in a base-promoted/18-crown-6 catalyzed process followed by addition of boron trifluoride etherate, undergo reactions with a wide range of organometallic nucleophiles to afford α-functionalized azacycles. Organozinc and organomagnesium nucleophiles add at ambient temperatures, obviating the need for cryogenic conditions.

Ring Expansion Alkyne Metathesis Polymerization.

The synthesis, characterization, and preliminary activity of an unprecedented tethered alkylidyne tungsten complex for ring expansion alkyne metathesis polymerization (REAMP) are reported. The tethered alkylidyne is generated rapidly by combining alkylidyne W(CBu)(CHBu)(O-2,6--CH) () with 1 equiv of an yne-ol proligand (). Characterized by NMR studies and nuclear Overhauser effect spectroscopy, complex is a dimer.

Mechanism of a Dually Catalyzed Enantioselective Oxa-Pictet-Spengler Reaction and the Development of a Stereodivergent Variant.

Enantioselective oxa-Pictet-Spengler reactions of tryptophol with aldehydes proceed under weakly acidic conditions utilizing a combination of two catalysts, an indoline HCl salt and a bisthiourea compound. Mechanistic investigations revealed the roles of both catalysts and confirmed the involvement of oxocarbenium ion intermediates, ruling out alternative scenarios. A stereochemical model was derived from density functional theory calculations, which provided the basis for the development of a highly enantioselective stereodivergent variant with racemic tryptophol derivatives.

Synthetic Factors Determining the Curvature and Nuclearity of the Giant Mn and Mn Clusters with a Torus Structure of ∼4 nm Diameter.

New members of the Mn and Mn torus-like cluster family have been prepared from a hybrid comproportionation-alcoholysis reaction of [MnO(OCR)(HO)] in alcohol in the presence of R'COH with NBuMnO or Mn salts as initiators. Reactions using MeCOH in PrOH or BuOH gave [MnO(OCMe)(OPr)(PrOH)(HO)] () and [MnO(OCMe)(OH)(OBu)(BuOH)(HO)] (), respectively, whereas EtCOH in PrOH gave [MnO(OCEt)(OPr)(PrOH)(HO)] (). They consist of alternating near-linear [Mn(μ-O)] and distorted-cubane [Mn(μ-O)(μ-OR)] units bridged by syn,syn-μ-RCO and μ-O groups and overall are [Mn] and [Mn] oligomers, the repeating unit containing two Mn and two Mn units.

iClick synthesis of network metallopolymers.

Described is an approach to preparing the first iClick network metallopolymers with porous properties. Treating digoldazido complex 2-AuN3 with trigoldacetylide 3-AuPPh3 or 3-AuPEt3, trialkyne 3-H, tetragoldacetylide 4-AuPPh3, or tetraalkyne 4-H in CHCl affords five iClick network metallopolymers 5-AuPPh3, 5-AuPEt3, 5-H, 6-AuPPh3, and 6-H. Confirmation of the iClick network metallopolymers comes from FTIR, C solid-state cross-coupling magic angle spinning (CPMAS) NMR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and nitrogen and CO sorption analysis.

Magnetic Properties of High-Nuclearity Fe-oxo ( = 7, 22, 24) Clusters Analyzed by a Multipronged Experimental, Computational, and Magnetostructural Correlation Approach.

The synthesis, structure, and magnetic properties of three related iron(III)-oxo clusters are reported, [FeO(OCPh)(mda)(HO)] (), [FeO(OH)(OCMe)(mda)](ClO) (), and [FeO(OH)(OEt)(OCMe)(mda)](ClO) (), where mdaH is -methyldiethanolamine. was prepared from the reaction of [FeO(OCPh)(HO)](NO) with mdaH in a 1:2 ratio in MeCN, whereas and were prepared from the reaction of FeCl/NaOCMe/mdaH in a 2:∼13:2 ratio and FeCl/NaOCMe/mdaH/pyridine in a 2:∼13:2:25 ratio, respectively, both in EtOH. The core of consists of a central octahedral Fe ion held within a nonplanar Fe loop by three μ-O and three μ-RO arms from the three mda chelates.

Isolation of an Elusive Phosphametallacyclobutadiene and Its Role in Reversible Carbon-Carbon Bond Cleavage.

The reactivity of phosphaalkynes, the isolobal and isoelectronic congeners to alkynes, with metal alkylidyne complexes is explored in this work. Treating the tungsten alkylidyne [ BuOCO]W≡C Bu(THF) (1) with phosphaalkyne (10) results in the formation of [O C( BuC=)W{η -(P,C)-P≡C-Ad}(THF)] (13- Bu ) and [O C(AdC=)W{η -(P,C)-P≡C- Bu}(THF)] (13-Ad ); derived from the formal reductive migratory insertion of the alkylidyne moiety into a W-C bond. Analogous to alkyne metathesis, a stable phosphametallacyclobutadiene complex [ BuOCO]W[κ -C( Bu)PC(Ad)] (14) forms upon loss of THF from the coordination sphere of either 13- Bu or 13-Ad .

Mn and Ce Units Supported on an Octahedral Molecular Nanoparticle of CeO.

The preparation of three new heterometallic clusters [CeMnO(OCPh)] (), [CeMnO(OCPh)] (), and [CeMnO(OH)(tbb)(HO)](NO) (; tbb = 4-Bu-benzoate) is reported. They all possess unprecedented structures with a common feature being the presence of an octahedral Ce-oxo core: a Ce in , two edge-fused Ce giving a Ce bioctahedron in , or a larger Ce octahedron in . Complex is the first Ce cluster with a central μ-O.

1,2,4-Trifunctionalized Cyclohexane Synthesis via a Diastereoselective Reductive Cope Rearrangement and Functional Group Interconversion Strategy.

Polyfunctionalized cyclohexanes are privileged scaffolds in drug discovery. Reported herein is a method for synthesizing 1,2,4-trifunctionalized cyclohexanes via diastereoselective reductive Cope rearrangement. The scaffolds obtained can be derivatized by orthogonal functional group interconversion to cyclohexanes bearing a 1-amide, 2-branched arylallyl, and variable 4-functional group.

Phosphorus-based ligand effects on the structure and radical scavenging ability of molecular nanoparticles of CeO.

Two new Ce/O clusters, (pyH)[CeO(OH)(OPPh)(NO)] (1) and [CeO(OH)(OPPh)(OCBu)] (2), have been prepared that contain P-based ligands for the first time. They were obtained from the reaction of (NH)[Ce(NO)], PhPOH or PhPOH, and BuCOH in a 2 : 1 : 2 molar ratio in pyridine/MeOH (10 : 1 mL). Both compounds contain a {CeO(OH)} face-capped octahedral core, with 1 containing an additional four Ce on the outside to give a supertetrahedral Ce topology; the {CeO} unit is the smallest recognizable fragment of the fluorite structure of CeO.

Double Tethered Metallacyclobutane Catalyst for Cyclic Polymer Synthesis.

This work outlines an approach to creating a catalyst for cyclic polymer synthesis using readily available materials in only one or two steps. Combining commercially available molybdenum-alkylidene with two equivalents of ene-ol proligand rapidly produces, in quantitative yield (H NMR spectroscopy), the double tethered metallacyclobutane complex . Characterized by variable temperature NMR studies and nuclear Overhauser effect spectroscopy (NOESY) experiments, complex exhibits fluxional behavior in solution.

Diol-Ritter Reaction: Regio- and Stereoselective Synthesis of Protected Vicinal Aminoalcohols and Mechanistic Aspects of Diol Monoester Disproportionation.

The well-known epoxide-Ritter reaction generally affords oxazolines with poor to average regioselectivity. Herein, a mechanism-based study of the less known diol-Ritter reaction has provided a highly regioselective procedure for the synthesis of 1--amido-2-esters from either terminal epoxides or 1,2-diols via Lewis acid-catalyzed monoesterification. When treated with a stoichiometric Lewis acid catalyst (BF), these diol monoesters form dioxonium cation intermediates that are ring-opened with nitrile nucleophiles to form nitrilium intermediates, which undergo rapid and irreversible hydration to give the desired amidoesters.

SPAAC iClick: progress towards a bioorthogonal reaction in-corporating metal ions.

Combining strain-promoted azide-alkyne cycloaddition (SPAAC) and inorganic click (iClick) reactivity provides access to metal 1,2,3-triazolates. Experimental and computational insights demonstrate that iClick reactivity of the tested metal azides (LM-N, M = Au, W, Re, Ru and Pt) depends on the accessibility of the azide functionality rather than electronic effects imparted by the metal. SPAAC iClick reactivity with cyclooctyne is observed when the azide functionality is sterically unencumbered, [Au(N)(PPh)] (Au-N3), [W(η-allyl)(N)(bpy)(CO)] (W-N3), and [Re(N)(bpy)(CO)] [bpy = 2,2'-bipyridine] (Re-N3).

Tuning Supramolecular Polymer Assembly through Stereoelectronic Interactions.

The supramolecular polymerization of 2,11-dithia[3.3]paracyclophanes through self-complementary intermolecular and transannular amide hydrogen bonding is presented. An interaction between the amide hydrogen bonding units and the central bridging atom results from the single-point exchange of a carbon atom for a sulfur atom.

α,α'-C-H Bond Difunctionalization of Unprotected Alicyclic Amines.

A simple one-pot procedure enables the sequential, regioselective, and diastereoselective introduction of the same or two different substituents to the α- and α'-positions of unprotected azacycles. Aryl, alkyl, and alkenyl substituents are introduced via their corresponding organolithium compounds. The scope of this transformation includes pyrrolidines, piperidines, azepanes, and piperazines.

Self-Assembled Bimetallic Aluminum-Salen Catalyst for the Cyclic Carbonates Synthesis.

Bimetallic bis-urea functionalized salen-aluminum catalysts have been developed for cyclic carbonate synthesis from epoxides and CO. The urea moiety provides a bimetallic scaffold through hydrogen bonding, which expedites the cyclic carbonate formation reaction under mild reaction conditions. The turnover frequency (TOF) of the bis-urea salen Al catalyst is three times higher than that of a μ-oxo-bridged catalyst, and 13 times higher than that of a monomeric salen aluminum catalyst.