Examination of Acid-Fast Bacilli in Sputum Using Modified Light Microscope with Homemade Light Emitting Diode Additional Attachment

Typical clinical symptoms and chest X-ray is a marker of Tuberculosis (TB) sufferers. However, the diagnosis of TB in adults should be supported by microscopic examination. Currently, Bacilli microscopic examination of acid-fast bacilli (AFB) in sputum by Ziehl-Neelsen (ZN) coloring is the most widely used. However, for reasons of convenience, especially for laboratories with a considerable amount of smear samples, and due to higher sensitivity compared with ZN staining, the World Health Organization (WHO) has recommended the use of auramine-O-staining (fluorochrome  staining), which is visualized by light emitting diode (LED) fluorescence microscopy. The aim of this study was to evaluate the performance of modified light microscope with homemade LED additional attachment for examination of AFB in sputum using auramine-O-staining method. We compared the sensitivity and specificity of 2 kinds of AFB in sputum methods: ZN and fluorochrome, using culture on Lowenstein-Jensen media as the gold standard. The results showed auramine-O-staining gives more proportion of positive findings (81%) compared to the ZN method (70%). These results demonstrated that the sensitivity of auramine-O-staining was higher than ZN, however it gives more potential false positive results than ZN. The sensitivity of auramine-O-staining in detecting AFB in sputum was 100% while the specificity was 88%

<i>N</i>‑Hydroxyphthalimide-Mediated Electrochemical Iodination of Methylarenes and Comparison to Electron-Transfer-Initiated C–H Functionalization

An electrochemical method has been developed for selective benzylic iodination of methylarenes. The reactions feature the first use of <i>N</i>-hydroxy­phthalimide as an electrochemical mediator for C–H oxidation to nonoxygenated products. The method provides the basis for direct (in situ) or sequential benzylation of diverse nucleophiles using methylarenes as the alkylating agent. The hydrogen-atom transfer mechanism for C–H iodination allows C–H oxidation to proceed with minimal dependence on the substrate electronic properties and at electrode potentials 0.5–1.2 V lower than that of direct electrochemical C–H oxidation

Insight into the Efficiency of Cinnamyl-Supported Precatalysts for the Suzuki–Miyaura Reaction: Observation of Pd(I) Dimers with Bridging Allyl Ligands During Catalysis

Despite widespread use of complexes of the type Pd­(L)­(η³-allyl)Cl as precatalysts for cross-coupling, the chemistry of related Pd^I dimers of the form (μ-allyl)­(μ-Cl)­Pd₂(L)₂ has been underexplored. Here, the relationship between the monomeric and the dimeric compounds is investigated using both experiment and theory. We report an efficient synthesis of the Pd^I dimers (μ-allyl)­(μ-Cl)­Pd₂(IPr)₂ (allyl = allyl, crotyl, cinnamyl; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) through activation of Pd­(IPr)­(η³-allyl)Cl type monomers under mildly basic reaction conditions. The catalytic performance of the Pd^II monomers and their Pd^I μ-allyl dimer congeners for the Suzuki–Miyaura reaction is compared. We propose that the (μ-allyl)­(μ-Cl)­Pd₂(IPr)₂-type dimers are activated for catalysis through disproportionation to Pd­(IPr)­(η³-allyl)Cl and monoligated IPr–Pd⁰. The microscopic reverse comproportionation reaction of monomers of the type Pd­(IPr)­(η³-allyl)Cl with IPr–Pd⁰ to form Pd^I dimers is also studied. It is demonstrated that this is a facile process, and Pd^I dimers are directly observed during catalysis in reactions using Pd^II precatalysts. In these catalytic reactions, Pd^I μ-allyl dimer formation is a deleterious process which removes the IPr–Pd⁰ active species from the reaction mixture. However, increased sterics at the 1-position of the allyl ligand in the Pd­(IPr)­(η³-crotyl)Cl and Pd­(IPr)­(η³-cinnamyl)Cl precatalysts results in a larger kinetic barrier to comproportionation, which allows more of the active IPr–Pd⁰ catalyst to enter the catalytic cycle when these substituted precatalysts are used. Furthermore, we have developed reaction conditions for the Suzuki-Miyaura reaction using Pd­(IPr)­(η³-cinnamyl)Cl which are compatible with mild bases

Mechanistic Studies of the Insertion of CO₂ into Palladium(I) Bridging Allyl Dimers

In contrast to the chemistry of momomeric η¹-Pd allyls, which act as nucleophiles, and monomeric η³-Pd allyls, which act as electrophiles, relatively little is known about the reactivity of Pd complexes with bridging allyl ligands. Recently we demonstrated that Pd^I dimers containing two bridging allyl ligands react with one equivalent of CO₂ to form species with one bridging allyl and one bridging carboxylate ligand. In this work we have prepared complexes from three different classes of Pd^I bridging allyl dimers: (i) dimers containing two bridging allyl ligands, (ii) dimers with one bridging allyl and one bridging chloride ligand, and (iii) dimers with one bridging allyl and one bridging carboxylate ligand. Complexes from all three groups have been characterized by X-ray crystallography, and their structures compared. Complexes with two bridging allyl ligands have the longest Pd bridging allyl bond lengths due to the high <i>trans</i> influence of the opposing bridging allyl ligand. For these species the HOMO is located almost entirely on the bridging allyl ligands, whereas for chloride- and carboxylate-bridged species the HOMO is primarily Pd based. A combined experimental and theoretical study has been performed to investigate the reactivity of the three different types of bridging allyl dimers with CO₂. Complexes with one bridging allyl and one bridging chloride ligand and complexes with one bridging allyl and one bridging carboxylate ligand do not insert CO₂ because the reaction is thermodynamically unfavorable. In contrast, in most cases the reaction of CO₂ with species containing two bridging allyl ligands is facile and involves nucleophilic attack of the bridging allyl ligand on electrophilic CO₂. An alternative pathway for CO₂ insertion, which involves a monomer/dimer equilibrium, can occur in the presence of a weakly coordinating ligand. Overall, our results suggest that although the bridging allyl ligand is likely to be unreactive in carboxylate- and chloride-bridged species, complexes with two bridging allyl ligands can act as nucleophiles like monomeric η¹-Pd allyls

Insight into the Efficiency of Cinnamyl-Supported Precatalysts for the Suzuki–Miyaura Reaction: Observation of Pd(I) Dimers with Bridging Allyl Ligands During Catalysis

Despite widespread use of complexes of the type Pd­(L)­(η³-allyl)Cl as precatalysts for cross-coupling, the chemistry of related Pd^I dimers of the form (μ-allyl)­(μ-Cl)­Pd₂(L)₂ has been underexplored. Here, the relationship between the monomeric and the dimeric compounds is investigated using both experiment and theory. We report an efficient synthesis of the Pd^I dimers (μ-allyl)­(μ-Cl)­Pd₂(IPr)₂ (allyl = allyl, crotyl, cinnamyl; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) through activation of Pd­(IPr)­(η³-allyl)Cl type monomers under mildly basic reaction conditions. The catalytic performance of the Pd^II monomers and their Pd^I μ-allyl dimer congeners for the Suzuki–Miyaura reaction is compared. We propose that the (μ-allyl)­(μ-Cl)­Pd₂(IPr)₂-type dimers are activated for catalysis through disproportionation to Pd­(IPr)­(η³-allyl)Cl and monoligated IPr–Pd⁰. The microscopic reverse comproportionation reaction of monomers of the type Pd­(IPr)­(η³-allyl)Cl with IPr–Pd⁰ to form Pd^I dimers is also studied. It is demonstrated that this is a facile process, and Pd^I dimers are directly observed during catalysis in reactions using Pd^II precatalysts. In these catalytic reactions, Pd^I μ-allyl dimer formation is a deleterious process which removes the IPr–Pd⁰ active species from the reaction mixture. However, increased sterics at the 1-position of the allyl ligand in the Pd­(IPr)­(η³-crotyl)Cl and Pd­(IPr)­(η³-cinnamyl)Cl precatalysts results in a larger kinetic barrier to comproportionation, which allows more of the active IPr–Pd⁰ catalyst to enter the catalytic cycle when these substituted precatalysts are used. Furthermore, we have developed reaction conditions for the Suzuki-Miyaura reaction using Pd­(IPr)­(η³-cinnamyl)Cl which are compatible with mild bases

Mechanistic Studies of the Insertion of CO₂ into Palladium(I) Bridging Allyl Dimers

In contrast to the chemistry of momomeric η¹-Pd allyls, which act as nucleophiles, and monomeric η³-Pd allyls, which act as electrophiles, relatively little is known about the reactivity of Pd complexes with bridging allyl ligands. Recently we demonstrated that Pd^I dimers containing two bridging allyl ligands react with one equivalent of CO₂ to form species with one bridging allyl and one bridging carboxylate ligand. In this work we have prepared complexes from three different classes of Pd^I bridging allyl dimers: (i) dimers containing two bridging allyl ligands, (ii) dimers with one bridging allyl and one bridging chloride ligand, and (iii) dimers with one bridging allyl and one bridging carboxylate ligand. Complexes from all three groups have been characterized by X-ray crystallography, and their structures compared. Complexes with two bridging allyl ligands have the longest Pd bridging allyl bond lengths due to the high <i>trans</i> influence of the opposing bridging allyl ligand. For these species the HOMO is located almost entirely on the bridging allyl ligands, whereas for chloride- and carboxylate-bridged species the HOMO is primarily Pd based. A combined experimental and theoretical study has been performed to investigate the reactivity of the three different types of bridging allyl dimers with CO₂. Complexes with one bridging allyl and one bridging chloride ligand and complexes with one bridging allyl and one bridging carboxylate ligand do not insert CO₂ because the reaction is thermodynamically unfavorable. In contrast, in most cases the reaction of CO₂ with species containing two bridging allyl ligands is facile and involves nucleophilic attack of the bridging allyl ligand on electrophilic CO₂. An alternative pathway for CO₂ insertion, which involves a monomer/dimer equilibrium, can occur in the presence of a weakly coordinating ligand. Overall, our results suggest that although the bridging allyl ligand is likely to be unreactive in carboxylate- and chloride-bridged species, complexes with two bridging allyl ligands can act as nucleophiles like monomeric η¹-Pd allyls

Effect of 2‑Substituents on Allyl-Supported Precatalysts for the Suzuki–Miyaura Reaction: Relating Catalytic Efficiency to the Stability of Palladium(I) Bridging Allyl Dimers

One of the most commonly used classes of precatalysts for cross-coupling are Pd­(II) complexes of the type (η³-allyl)­Pd­(L)­Cl. Here, we report the first full investigation of how the steric and electronic properties of the 2-substituent affect the catalytic properties of precatalysts of the type (η³-allyl)­Pd­(L)­Cl. Specifically, we have prepared and studied a series of well-defined 2-substituted precatalysts of the type (η³-2-R-allyl)­Pd­(IPr)Cl (R = H, Ph, Me, ^tBu, OMe, CN), as well as their related Pd­(I) (μ-2-R-allyl)­(μ-Cl)­Pd₂(IPr)₂ dimers. The catalytic performance of the Pd­(II) monomers and their Pd­(I) μ-allyl dimer congeners is compared for the Suzuki–Miyaura reaction. When Pd­(II) monomers are used as precatalysts, we observe the formation of the Pd­(I) μ-allyl dimers during catalysis. In fact, we find that the catalytic efficiency of (η³-2-R-allyl)­Pd­(IPr)Cl precatalysts correlates inversely with the thermodynamic stability of the related Pd­(I) μ-allyl dimers. Therefore, we have examined the structural and electronic properties of the Pd­(I) μ-allyl dimers in detail and probed the mechanism of the (μ-2-R-allyl)­(μ-Cl)­Pd₂(IPr)₂ dimer/(η³-2-R-allyl)­Pd­(IPr)­Cl monomer interconversion both experimentally and computationally. Overall, this study shows that the formation of Pd­(I) μ-allyl dimers can play a crucial role in determining the catalytic efficiency of precatalysts of the type (η³-allyl)­Pd­(IPr)­Cl

Design of a Versatile and Improved Precatalyst Scaffold for Palladium-Catalyzed Cross-Coupling: (η³‑1‑^tBu-indenyl)₂(μ-Cl)₂Pd₂

We describe the development of (η³-1-^tBu-indenyl)₂(μ-Cl)₂Pd₂, a versatile precatalyst scaffold for Pd-catalyzed cross-coupling. Our new system is more active than commercially available (η³-cinnamyl)₂(μ-Cl)₂Pd₂ and is compatible with a range of NHC and phosphine ligands. Precatalysts of the type (η³-1-^tBu-indenyl)­Pd­(Cl)­(L) can either be isolated through the reaction of (η³-1-^tBu-indenyl)₂(μ-Cl)₂Pd₂ with the appropriate ligand or generated in situ, which offers advantages for ligand screening. We show that the (η³-1-^tBu-indenyl)₂(μ-Cl)₂Pd₂ scaffold generates highly active systems for a number of challenging cross-coupling reactions. The reason for the improved catalytic activity of systems generated from the (η³-1-^tBu-indenyl)₂(μ-Cl)₂Pd₂ scaffold compared to (η³-cinnamyl)₂(μ-Cl)₂Pd₂ is that inactive Pd^I dimers are not formed during catalysis

Direct Heterocycle C–H Alkenylation via Dual Catalysis Using a Palladacycle Precatalyst: Multifactor Optimization and Scope Exploration Enabled by High-Throughput Experimentation

One of the major challenges in developing catalytic methods for C–C bond formation is the identification of generally applicable reaction conditions, particularly if multiple substrate structural classes are involved. Pd-catalyzed direct arylation reactions are powerful transformations that enable direct functionalization of C–H bonds; however, the corresponding direct alkenylation reactions, using vinyl (pseudo) halide electrophiles, are less well developed. Inspired by process development efforts toward GSK3368715, an investigational active pharmaceutical ingredient, we report that a Pd(II) palladacycle derived from tri-tert-butylphosphine and Pd(OAc)2 is an effective single-component precatalyst for a variety of direct alkenylation reactions. High-throughput experimentation identified optimal solvent/base combinations for a variety of HetAr–H substrate classes undergoing C–H activation without the need for cocatalysts or stoichiometric silver bases (e.g., Ag2CO3). We propose this reaction proceeds via a dual cooperative catalytic mechanism, where in situ-generated Pd(0) supports a canonical Pd(0)/(II) cross-coupling cycle and the palladacycle effects C–H activation via CMD in a redox-neutral cycle. In all, 192 substrate combinations were tested with a hit rate of approximately 40% and 24 isolated examples. Importantly, this method was applied to prepare a key intermediate in the synthesis of GSK3368715 on multigram scale