Photoredox Catalyzed Single C-F Bond Activation of Trifluoromethyl Ketones: A Solvent Controlled Divergent Access of gem-Difluoromethylene Containing Scaffolds.

Selective defluorinative functionalization of trifluoromethyl ketones is a long-standing challenge owing to the exhaustive mode of the process. To meet the demands for the installation of the gem-difluoromethylene unit for the construction of the molecular architectures of well-known pharmaceuticals and agrochemicals, a distinct pathway is thereby highly desirable. Here, a protocol is introduced that allows the divergent synthesis of gem-difluoromethylene group containing tetrahydrofuran derivatives and linear ketones via single C-F bond activation of trifluoromethyl ketones using visible-light photoredox catalysis in the presence of suitable olefins as trapping partner. The choice of appropriate solvent and catalyst plays a significant role in controlling the divergent behavior of this protocol. Highly reducing photo-excited catalysts are found to be responsible for the generation of α,α-difluoromethyl ketone (DFMK) radicals as the key intermediate via a SET process. This protocol also results in a high diastereoselectivity towards the formation of partially fluorinated cyclic ketal derivatives with simultaneous construction of one C-C and two C-O bonds. State-of-the-art DFT calculations are performed to address the origin of diastereoselectivity as well as the divergence of this protocol.

In-Catalyzed Transfer Hydrogenation and Regioselective Hydrogen-Deuterium Addition to the Olefins.

A unique and valuable methodology is developed for the hydrogenation of aromatic as well as aliphatic 1,1-di- and trisubstituted alkenes. In the presence of catalytic InBr3, readily available 1,3-benzodioxole and residual H2O present in the reaction mixture are utilized as a hydrogen gas surrogate and proved to be a practical source of deuterium incorporation into the olefins on either side by varying the source of the starting deuterated 1,3-benzodioxole or D2O. Experimental studies show the transfer of hydride from 1,3-benzodioxole to the carbocationic intermediate generated from the protonation of alkenes by the H2O-InBr3 adduct remains the critical step.

Palladium-catalyzed regioselective synthesis of mono and bis(arylthiol) alkenes from propargyl carbonate and thiophenol.

A palladium catalyzed regioselective reaction of propargylic carbonate with thiophenols and benzene selenol is described. Atom-economic addition of thiols to propargylic carbonates provides an excellent opportunity for effective processes. The reaction proceeds via hydrothiolation to produce mono(arylthiol) alkenes and hydrothiolation followed by Tsuji-Trost type substitution to form bis(arylthiol) alkenes through single and double sequential attack by soft thio nucleophiles by control of the equivalence of thiophenols. This coupling reaction with good tolerance towards functional groups in both propargylic carbonates and thiols furnished a variety of highly functionalized alkenylation products in moderate to excellent yields via the formation of new C-S and C-Se bonds.

Metal-free thiolation of sulfonyl hydrazone with thiophenol: synthesis of 4-thio-chroman and diarylmethyl thioethers.

A simple, efficient, and transition metal-free approach was developed for accessing 4-thio-substituted chroman and diarylmethyl thioethers from sulfonyl hydrazones. This protocol provides straightforward access to a class of diarylmethane derivatives with good to excellent yields. This operationally simple protocol exhibited good tolerance for labile functional groups, providing biologically relevant chemical libraries. This safe and feasible route is applicable to the large-scale synthesis of 4-thio-substituted chromans, which are of great synthetic interest because of their further reaction potential.

HFIP-Assisted Single C-F Bond Activation of Trifluoromethyl Ketones using Visible-Light Photoredox Catalysis.

A visible light photoredox catalytic method for the selective cleavage of single strong C-F bond in trifluoromethyl ketones is reported. Single electron reduction of trifluoromethyl ketones generates difluoromethyl radicals which can be engaged in intermolecular C-C bond formation with N-methyl-N-arylmethacrylamides to furnish fluorine-containing oxindole derivatives in good yields. The reaction shows excellent chemoselectivity with good functional group tolerance under mild conditions. 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) as a solvent plays a critical role for the selective single C-F bond cleavage. High-level DFT calculations are depicted to shed light on the mechanism.

Utilization of CO2 Feedstock for Organic Synthesis by Visible-Light Photoredox Catalysis.

CO2 is a highly abundant, green, and sustainable carbon feedstock. Despite its kinetic inertness and thermodynamic stability, the development of various catalytic techniques has enabled the conversion of CO2 to value-added products such as carboxylic acids, amino acids, and heterocyclic compounds, where visible-light photocatalysis has emerged to be an efficient promoter of these processes. This Minireview covers the progress in the areas of CO2 incorporation onto organic matters based on the combined venture of renewable resources of CO2 and light energy with significant emphasis on the last three years' developments.

Tris(pentafluorophenyl)borane catalyzed C-C and C-heteroatom bond formation.

A series of boron based Lewis acids have been reported to date, but among them, tris(pentafluorophenyl)borane (BCF) has gained the most significant attention in the synthetic chemistry community. The viability of BCF as a potential Lewis acid catalyst has been vastly explored in organic and materials chemistry due to its thermal stability and commercial availability. Most explorations of BCF chemistry in organic synthesis has occurred in the last two decades and many new catalytic reactivities are currently under investigation. This review mainly focuses on recent reports from 2018 onwards and provides a concise knowledge to the readers about the role of BCF in metal-free catalysis. The review has mainly been categorized by different types of organic transformation mediated through BCF catalysis for the C-C and C-heteroatom bond formation.

Impact of Tinnitus Masking on Auditory Brainstem Response Results.

INTRODUCTION: Tinnitus- the perception of sound without external stimulation can also lead to disruption in the quality of life and has been over the years been benefitted by tinnitus masking. Hence this study to understand the effectiveness of tinnitus masking using the Auditory Brainstem Response (ABR) Test. OBJECTIVES: The intention of this experimental research design is to determine whether tinnitus masking as treatment for tinnitus makes a significant difference in auditory evoked brainstem responses before and after masking for understanding the effectiveness of the treatment objectively and possible quantification of benefit measurement through ABR. DESIGN: 30 subjects with normal hearing and unilateral tinnitus were assessed using ABR before and after tinnitus masking. Data was collected and compared to evaluate pre-masking and post-masking values of Latency-Intensity function and Interpeak Latency differences. Data was analyzed using descriptive statistics, test of homogeneity of variances and Two-way ANOVA. RESULTS: Both latency-intensity functions and interpeak latency differences showed significant differences before and after tinnitus masking with significance values of Two-way ANOVA as .001, (Calculated at p < .05). CONCLUSIONS: Despite the patient's subjective feedback, objective proof of the patient's benefit is a necessity. Therefore, this study shows that ABR shows significant differences in patients treated with tinnitus masking. Further suggesting benefit quantification of tinnitus masking as a treatment to tinnitus suffering individuals and for further understanding the intricacies of changes in the central auditory pathway due to masking.

Management of Tinnitus In Covid-19 Outbreak- A Comparative Study Between Mindfulness Based Tinnitus Stress Reduction And Tinnitus Retraining Therapy.

BACKGROUND: Covid-19 pandemic has caused a profound impact on the lives of people and has given rise to many mental health issues like anxiety and stress which eventually has given rise to bothersome tinnitus. In case of people having pre-existing tinnitus, the pandemic has raised the problem of tinnitus and the co-morbid issues related to tinnitus and severely affected the overall quality of life. Hence, we need to find a mean for home-based management of tinnitus and its associated problems. OBJECTIVE: To understand the mechanism of mental health and to compare between the mindfulness-based tinnitus reduction and tinnitus retraining therapy on android-based application. DESIGN: Comparative and Experimental design. METHOD: The study was conducted on 60 participants and was divided into two groups. Detailed audiological assessment, tinnitus assessment and Tinnitus Handicap Inventory (THI) and Tinnitus Cognitions Questionnaire (TCQ) were administered. Group-I was provided with tinnitus retraining therapy and group-II was provided with mindfulness based tinnitus stress reduction. After the post therapy evaluation the data were compiled for statistical analysis in SPSS software 20.0. Results: It was found that there were significant difference between the pre and post therapy scores of TRT and MBTSR in both THI and TCQ (p<0.001). CONCLUSION: Home-based management of tinnitus during the COVID-19 pandemic using both TRT and MBTSR were highly successful and had similar results MBTSR was found to be more useful as it had better outcome in reducing the tinnitus related annoyance and shown better improvement in QOL examination.

Percutaneous Cystolithotomy in Augmented Bladders.

AIMS: Incidence and recurrence of bladder stone in augmented exstrophy bladder rate is high. So, recurrent open cystolithotomy is not a preferred procedure; particularly through scarred tissues, consequence of previous surgeries. Percutaneous cystolithotomy (PCCL) is an old but standard procedure for retrieval of bladder stones in adults. We extrapolated PCCL for bladder stone in augmented bladders in children. PATIENTS AND METHODS: In three patients, we made suprapubic (SP) needle track with initial puncture (IP) needle under cystoscopic guidance. Following that laparoscopic cannula was placed through dilated SP track that was crafted with Alken's dilators and bladder stones were removed with grasper. RESULTS: On cystoscopy, we also observed the patches of skin tissues in native bladders. Continence and bladder capacity were not affected following PCCL. CONCLUSION: PCCL in augmented bladder showed good outcome. High recurrence of bladder stone is possibly due to presence of keratin in dermal tissue; invaded mucosa in open bladder plate. It seems shaving or fulguration of those dermal elements during bladder reconstruction might decrease incidence of stone formation. However, we haven't attempted fulguration during PCCL.

A survey of chiral hypervalent iodine reagents in asymmetric synthesis.

The recent years have witnessed a remarkable growth in the area of chiral hypervalent iodine chemistry. These environmentally friendly, mild and economic reagents have been used in catalytic or stoichiometric amounts as an alternative to transition metals for delivering enantioenriched molecules. Varieties of different chiral reagents and their use for demanding asymmetric transformations have been documented over the last 25 years. This review highlights the contribution of different chiral hypervalent iodine reagents in diverse asymmetric conversions.

B(C6 F5 )3 -Catalyzed Chemoselective Defunctionalization of Ether-Containing Primary Alkyl Tosylates with Hydrosilanes.

Catalytic C(sp3 )-O bond cleavage promoted by B(C6 F5 )3 /Et3 SiH proceeds preferentially with primary tosylates in the presence of primary and secondary silyl ethers and aryl ethers. This reactivity difference enables the chemoselective defunctionalization of several 1,n-diols, and the efficiency of the new procedure is highlighted by the selective deoxygenation of the hydroxymethyl group of an orthogonally protected carbohydrate. Tosylates with an adjacent phenyl group are cleaved with anchimeric assistance.

Extending the Scope of the B(C6 F5 )3 -Catalyzed C=N Bond Reduction: Hydrogenation of Oxime Ethers and Hydrazones.

The B(C6 F5 )3 -catalyzed hydrogenation is applied to aldoxime triisopropylsilyl ethers and hydrazones bearing an easily removable phthaloyl protective group. The CN reduction of aldehyde-derived substrates (oxime ethers and hydrazones) is enabled by using 1,4-dioxane as the solvent known to participate as the Lewis-basic component in FLP-type heterolytic dihydrogen splitting. More basic ketone-derived hydrazones act as Lewis bases themselves in the FLP-type dihydrogen activation and are therefore successfully hydrogenated in nondonating toluene. The difference in reactivity between aldehyde- and ketone-derived substrates is also reflected in the required catalyst loading and dihydrogen pressure.

B(C6F5)3-catalyzed transfer hydrogenation of imines and related heteroarenes using cyclohexa-1,4-dienes as a dihydrogen source.

The strong boron Lewis acid tris(pentafluorophenyl)borane, B(C6F5)3, is shown to abstract a hydride from suitably donor-substituted cyclohexa-1,4-dienes, eventually releasing dihydrogen. This process is coupled with the FLP-type (FLP = frustrated Lewis pair) hydrogenation of imines and nitrogen-containing heteroarenes that are catalyzed by the same Lewis acid. The net reaction is a B(C6F5)3-catalyzed, i.e., transition-metal-free, transfer hydrogenation using easy-to-access cyclohexa-1,4-dienes as reducing agents. Competing reaction pathways with or without the involvement of free dihydrogen are discussed.

B(C6F5)3 -catalyzed transfer of dihydrogen from one unsaturated hydrocarbon to another.

A transition-metal-free transfer hydrogenation of 1,1-disubstituted alkenes with cyclohexa-1,4-dienes as the formal source of dihydrogen is reported. The process is initiated by B(C6 F5 )3 -mediated hydride abstraction from the dihydrogen surrogate, forming a Brønsted acidic Wheland complex and [HB(C6 F5 )3 ](-) . A sequence of proton and hydride transfers onto the alkene substrate then yields the alkane. Although several carbenium ion intermediates are involved, competing reaction channels, such as dihydrogen release and cationic dimerization of reactants, are largely suppressed by the use of a cyclohexa-1,4-diene with methyl groups at the C1 and C5 as well as at the C3 position, the site of hydride abstraction. The alkene concentration is another crucial factor. The various reaction pathways were computationally analyzed, leading to a mechanistic picture that is in full agreement with the experimental observations.

X-ray characterization of an electron donor-acceptor complex that drives the photochemical alkylation of indoles.

A metal-free, photochemical strategy for the direct alkylation of indoles was developed. The reaction, which occurs at ambient temperature, is driven by the photochemical activity of electron donor-acceptor (EDA) complexes, generated upon association of substituted 1H-indoles with electron-accepting benzyl and phenacyl bromides. Significant mechanistic insights are provided by the X-ray single-crystal analysis of an EDA complex relevant to the photoalkylation and the determination of the quantum yield (Φ) of the process.

Stereospecific formal [3+2] dipolar cycloaddition of cyclopropanes with nitrosoarenes: an approach to isoxazolidines.

The MgBr2-catalyzed formal [3+2] cycloaddition of donor-acceptor activated cyclopropanes with nitrosoarenes offers a novel approach to various structurally diverse isoxazolidines. The reactions, which are experimentally easy to conduct, occur with complete stereospecificity and perfect control of regioselectivity. Product isoxazolidines can be readily transformed into α-amino lactones by reductive or decarboxylative N-O cleavage and subsequent lactonisation, and the N-aryl bond cleavage is also possible under oxidative conditions.

Bouveret's syndrome: a rare presentation of a common surgical enigma.

Bouveret syndrome, an uncommon complication of cholelithiasis, typically manifests with symptoms of gastric outlet obstruction. Despite its rarity, Bouveret syndrome carries significant morbidity and mortality. This paper presents a case study and explores diagnostic approaches and management options for this challenging condition.