Aryl carbonyls and carbinols as proelectrophiles for Friedel-Crafts benzylation and alkylation

Friedel-Crafts benzylation/alkylation using benzylic, tertiary, and homobenzylic alcohols; aryl aldehydes, aryl ketones, and the highly challenging aryl carboxylic acids and esters as proelectrophiles has been achieved using borane-ammonia and TiCl4, greatly broadening the scope of useable substrates. Incorporation of deactivated aromatic proelectrophiles and specificity for substitution at the benzylic position are demonstrated in the synthesis of various di- and triarylalkane products. Dual protocols allow for the use of standard nucleophilic solvents (benzene, toluene, etc.) or for stoichiometric addition of more valuable nucleophiles including furans, thiophenes, and benzodioxoles.

Synthesis and Energetic Characterization of Borane-Amines on High-Nitrogen Heterocycles

Borane-amines have garnered attention over the last several decades in a variety of applications, ranging from hydrogen storage materials to hypergolic fuel systems. An investigation into the synthesis of borane-amines with high-nitrogen content heterocycles was undertaken in this work. Borane-amines were formed by the reaction of BH3·Me2S in tetrahydrofuran (THF) with the requisite nitrogen-containing heterocycle and isolated by placing the crude reaction mixture in hexanes to precipitate the product. X-ray crystallography, thermogravimetric analysis (TGA), high resolution mass spectroscopy (HRMS), 1H NMR, 13C NMR, and 11B NMR were utilized for product characterization, while impact and friction sensitivity testing were conducted to identify sensitivity in the synthesized compounds. Most isolated borane-amines, except one, were found to decompose in the atmosphere and were more sensitive to mechanical stimuli than their starting materials; however, all synthesized compounds were found to be hypergolic in the presence of white fuming nitric acid (WFNA).

TiF4-catalyzed direct amidation of carboxylic acids and amino acids with amines

Unlike other metal fluorides, catalytic titanium tetrafluoride enhances the direct amidation of aromatic and aliphatic carboxylic acids and N-protected amino acids in refluxing toluene. While aromatic acids were converted to amides with 10 mol% of the catalyst within 24 h, aliphatic acids underwent a faster reaction (12 h), with lower catalyst loading (5 mol%). This protocol is equally efficient with alkyl and aryl amines providing a variety of carboxamides and peptides in 60-99% yields.

Borane-Pyridine: An Efficient Catalyst for Direct Amidation

Borane-pyridine acts as an efficient (5 mol%) liquid catalyst, providing improved solubility for the direct amidation of a wide range of aromatic and aliphatic carboxylic acids and amines to form secondary and tertiary carboxamides. Tolerance of potentially incompatible halo, nitro, and alkene functionalities has been demonstrated.

One-Pot, Tandem Reductive Amination/Alkylation-Cycloamidation for Lactam Synthesis from Keto or Amino Acids

Monotrifluoroacetoxyborane-amines, prepared by treating borane-amines with trifluoroacetic acid, have been shown to be efficient reagents for a one-pot, tandem reductive amination/alkylation-cycloamidation of keto or amino acids to achieve the synthesis of 5-aryl or 5-methyl pyrrolidin-2-ones and 6-aryl or 6-methyl piperidin-2-ones.

Catalyst- and Stoichiometry-Dependent Deoxygenative Reduction of Esters to Ethers or Alcohols with Borane-Ammonia

A facile and selective room temperature deoxygenation of both aromatic and aliphatic carboxylic esters to ethers has been achieved by regulating the stoichiometry of the reductant, BH3-NH3, and the catalyst, TiCl4. This first, practical borane-mediated process is compatible with various potentially sensitive functional groups and is applicable to the deoxygenative ether formation from typically challenging aromatic acid esters. Substituting BF3-Et2O as the catalyst alters the reaction pathway, reducing the esters to alcohols. Mechanistic insights are provided by NMR spectroscopy, deuterium labeling, and kinetic isotope studies.

Balancing Lewis Acidity and Carbocation Stability for the Selective Deoxyhalogenation of Aryl Carbonyls and Carbinols

Deoxyhalogenation of aryl aldehydes, ketones, carboxylic acids, and esters has been achieved utilizing an appropriate metal halide Lewis acid acting as a carbonyl activator and halogen carrier in combination with borane-ammonia as the reductant. Selectivity is accomplished by matching the stability of the carbocation intermediate with the effective acidity of the Lewis acid. Substituents and substitution patterns significantly influence the requisite solvent/Lewis acid combination. Logical combinations of these factors have also been applied for the regioselective conversion of alcohols to alkyl halides.

Titanium-Mediated Reduction of Carboxamides to Amines with Borane-Ammonia

In this study, the successful titanium tetrachloride-catalyzed reduction of aldehydes, ketones, carboxylic acids, and nitriles with borane-ammonia was extended to the reduction (deoxygenation) of a variety of aromatic and aliphatic pri-, sec- and tert-carboxamides, by changing the stoichiometry of the catalyst and reductant. The corresponding amines were isolated in good to excellent yields, following a simple acid-base workup.

Dehydroborylation of Terminal Alkynes Using Lithium Aminoborohydrides

Dehydrogenative borylation of terminal alkynes has recently emerged as an atom-economical one-step alternative to traditional alkyne borylation methodologies. Using lithium aminoborohydrides, formed in situ from the corresponding amine-boranes and n-butyllithium, a variety of aromatic and aliphatic terminal alkyne substrates were successfully borylated in high yield. The potential to form mono-, di-, and tri-B-alkynylated products has been shown, though the mono-product is primarily generated using the presented condition. The reaction has been demonstrated at large (up to 50 mmol) scale, and the products are stable to column chromatography as well as acidic and basic aqueous conditions. Alternately, the dehydroborylation can be achieved by treating alkynyllithiums with amine-boranes. In that respect, aldehydes can act as starting materials by conversion to the 1,1-dibromoolefin and in situ rearrangement to the lithium acetylide.

Room Temperature Reduction of Titanium Tetrachloride-Activated Nitriles to Primary Amines with Ammonia-Borane

The reduction of a variety of aromatic and aliphatic nitriles, activated by a molar equivalent of titanium tetrachloride, has been achieved at room temperature using ammonia borane as a safe reductant. The corresponding methanamines were isolated in good to excellent yields following a simple acid-base workup.

A Safer Reduction of Carboxylic Acids with Titanium Catalysis

Ammonia-borane, shown previously to react with carboxylic acids under reflux to form primary amides, reduces acids to alcohols at room temperature in the presence of catalytic TiCl4. The process, which is tolerant of a variety of potentially reactive functional groups, including N-protected amino acids, can be employed for the selective reduction of acids in the presence of amides, nitriles and, to some extent, esters. Aliphatic acids can be selectively reduced in the presence of aromatic acids.

TiCl4-Catalyzed Hydroboration of Ketones with Ammonia Borane

Investigation of a variety of Lewis acids for the hydroboration-hydrolysis (reduction) of ketones with amine-boranes has revealed that catalytic (10 mol %) titanium tetrachloride (TiCl₄) in diethyl ether at room temperature immensely accelerates the reaction of ammonia borane. The product alcohols are produced in good to excellent yields within 30 min, even with ketones which typically requires 24 h or longer to reduce under uncatalyzed conditions. Several potentially reactive functionalities are tolerated, and substituted cycloalkanones are reduced diastereoselectively to the thermodynamic product. A deuterium labeling study and ¹¹B NMR analysis of the reaction have been performed to verify the proposed hydroboration mechanism.

Aminoboranes via Tandem Iodination/Dehydroiodination for One-Pot Borylation

A rapid synthesis of aminoboranes from amine-boranes utilizing an iodination/dehydroiodination sequence is described. Monomeric aminoboranes are generated exclusively from several substrate adducts, following an E2-type elimination, with the added base playing a critical role in monomer vs dimer formation. Diisopropylaminoborane formed using this methodology has been applied to a one-pot palladium-catalyzed conversion of iodo- and bromoarenes to the corresponding boronates. Additionally, modification of the workup allows for isolation of the boronic acid and recovery of the utilized amine.

Activation of sodium borohydride via carbonyl reduction for the synthesis of amine- and phosphine-boranes

A highly versatile synthesis of amine-boranes via carbonyl reduction by sodium borohydride is described. Unlike the prior bicarbonate-mediated protocol, which proceeds via a salt metathesis reaction, the carbon dioxide-mediated synthesis proceeds via reduction to a monoformatoborohydride intermediate. This has been verified by spectroscopic analysis, and by using aldehydes and ketones as the carbonyl source for the activation of sodium borohydride. This process has been used to produce borane complexes with 1°-, 2°-, and 3°-amines, including those with borane reactive functionalities, heteroarylamines, and a series of phosphines.

Ammonia-borane as a Catalyst for the Direct Amidation of Carboxylic Acids

Ammonia-borane serves as an efficient substoichiometric (10%) precatalyst for the direct amidation of both aromatic and aliphatic carboxylic acids. In situ generation of amine-boranes precedes the amidation and, unlike the amidation with stoichiometric amine-boranes, this process is facile with 1 equiv of the acid. This methodology has high functional group tolerance and chromatography-free purification but is not amenable for esterification. The latter feature has been exploited to prepare hydroxyl- and thiol-containing amides.

Trimethyl Borate-Catalyzed, Solvent-Free Reductive Amination

Solvent-free reductive amination of aldehydes and ketones with aliphatic and aromatic amines in high-to-excellent yields has been achieved with sub-stoichiometric trimethyl borate as promoter and ammonia borane as reductant.

Amine-boranes as Dual-Purpose Reagents for Direct Amidation of Carboxylic Acids

Amine-boranes serve as dual-purpose reagents for direct amidation, activating aliphatic and aromatic carboxylic acids and, subsequently, delivering amines to provide the corresponding amides in up to 99% yields. Delivery of gaseous or low-boiling amines as their borane complexes provides a major advantage over existing methodologies. Utilizing amine-boranes containing borane incompatible functionalities allows for the preparation of functionalized amides. An intermolecular mechanism proceeding through a triacyloxyborane-amine complex is proposed.

β,γ-Diaryl α-methylene-γ-butyrolactones as potent antibacterials against methicillin-resistant Staphylococcus aureus

A selected series of racemic α-methylene-γ-butyrolactones (AMGBL) synthesized via allylboration or allylindation reactions were screened against methicillin-resistant Staphylococcus aureus (MRSA) USA300. Unlike natural AMGBLs, such as parthenolide, synthetic analogs bearing aryl moieties at the β- and γ-positions are potent against MRSA. The most potent molecules were comparable to vancomycin and linezolid, the drugs of the last resort for MRSA infections, in their effectiveness with minimum inhibitory concentrations (MICs) ranging from 3.0 to 5.2 μM. These lactones also exhibited potent antibacterial activity against other clinically important multidrug-resistant Gram-positive bacteria (except enterococci), while also showing high tolerability to mammalian cells. Several of these molecules surpassed vancomycin in their rapid killing of the high MRSA inoculum (2 h vs 12 h) in a standard time-kill kinetics assay, with compounds 1l and 1m significantly reducing the intracellular burden of MRSA by about 98-99%, at low concentrations. Additionally, the compounds surpassed vancomycin in inhibiting staphylococcal protease production, indicating that synthetic methylene lactones warrant further investigations as promising anti-MRSA candidates.

Preoperative ultrasonography for tumor thickness evaluation in guiding management in patients with early oral tongue squamous cell carcinoma

Objectives:

(1) To assess the statistical correlation between the tumor thickness (TT) by ultrasonography (USG) and microscopic measurement in cases of early oral tongue squamous cell carcinoma (OTSCC). (2) To assess the predictive capacity of TT by ultrasound in detecting nodal metastasis.

Materials and Methods:

Prospective analysis was performed in 24 patients for a period of 2 years from 2012 to 2013. Nodal status and TT measurement was done preoperatively by neck and intraoral USG respectively in cases of early (pT1 & T2, clinically N0) OTSCC. As per the institution protocol after histopathological confirmation of malignancy, all patients underwent resection of primary lesion and ipsilateral elective neck dissection (Level - I to IV). Measurement of TT was obtained intraoperatively from fresh glossectomy specimen and postoperatively from histopathological paraffin section examination. The statistical correlation between TT measured by USG and histopathology was assessed by Pearson's correlation coefficient. Chi-square test was used to find the association of pathological T stage, TT with pathological nodal status.

Results:

Significant statistical correlation was seen between TT by USG and microscopic measures. Between the two, TT measurements were within 1 mm in 37.5% (9/24) of cases, within 2 mm in 29.16% (7/24), and was greater than 2 mm in 8 cases. The Pearson's correlation r is 0.678 (P < 0.001) and ICC (interclass correlation coefficient) is 0.808. The average difference between microscopic and US thickness (Bias) is -0.14637 and the limits of agreement is (4.717, -4.863) with 95% limits of agreement. The rate of occult nodal metastasis was 16.6% and TT of <4 mm had no incidence of nodal metastasis.

Conclusion:

Ultrasonographic evaluation is reliable and cost-effective tool to measure the TT preoperatively, which will be of help in deciding the management in early OTSCC. TT of 4 mm and above was predictor of occult cervical nodal metastasis.

CT-guided Lung Fine Needle Aspiration Biopsy: Analysis of Efficacy, Yield and Intricacies

Aim: This study aims to evaluate various factors that affect the cytological yield while performing computed tomography (CT) guided lung fine needle aspiration biopsy and to determine the complication rate of this procedure. Materials and Methods: In this cross sectional study, we analyzed 70 patients undergoing CT-guided transthoracic lung fine-needle aspiration biopsy (FNAB). 22-gauge spinal needle was used in sixty patients and 20-gauge in ten patients. The presence and absence of an onsite cytopathologist affecting the adequacy of yield for a conclusive cytodiagnosis was compared in groups of 35 patients each. The incidence of complications such as pneumothorax, pulmonary hemorrhage was recorded. Results: Cytological yield was adequate for a conclusive cytodiagnosis in 59 cases (84.2%). Thirty-seven cases (52.8%) were malignant with adenocarcinoma (70.2%) being the most common, 22 cases (31.4%) had benign etiology. Cytological yield was adequate for a conclusive diagnosis in the group (n = 35) with an onsite cytopathologist (100%) compared with those cases without an onsite cytopathologist (68.6%) (P = 0.005). Pneumothorax was observed in 16 cases (22.8%), the incidence of pneumothorax was higher when there was an intervening parenchyma (P = 0.005). Conclusion: CT-guided transthoracic FNAB is an accurate method to rule out malignancy with a reasonable rate of complications. The presence of an onsite-cytopathologist significantly improves the adequacy of yield for a conclusive cytodiagnosis, and should be routinely employed. Pneumothorax and pulmonary hemorrhage are the most common complications as a result of FNAB. The incidence of pneumothorax is higher when there is intervening lung parenchyma.

A non-dissociative open-flask hydroboration with ammonia borane: ready synthesis of ammonia-trialkylboranes and aminodialkylboranes

Under open-flask conditions, ammonia borane hydroborates olefins in refluxing tetrahydrofuran. Unlike conventional hydroboration, the Lewis base (ammonia) is not dissociated from the boron center. Terminal alkenes selectively provide ammonia-trialkylborane complexes. On the other hand, internal alkenes afford aminodialkylboranes via a metal-free hydroboration-dehydrogenation sequence. Alkaline hydrogen peroxide oxidation of the products provides the corresponding alcohols in high yields.

The role of ammonia in promoting ammonia borane synthesis

Mechanistic studies point toward added ammonia acting as a reagent while promoting the high-yielding synthesis of pure ammonia borane from sodium borohydride and ammonium salts.

Amine–boranes bearing borane-incompatible functionalities: application to selective amine protection and surface functionalization

The first general open-flask synthesis of amine–boranes with inexpensive and readily available reagents, such as sodium borohydride, sodium bicarbonate, water, and the desired amines is described.

Role of dual time fluorodeoxyglucose (FDG) positron emission tomography-computed tomography in identifying co-existing inflammatory and malignant disease: Who holds it (FDG) longer?

18-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) is an integral part of imaging in the follow-up of head and neck malignancies. Very often distinguishing inflammatory/infective from malignant recurrence cannot be made confidently with standard uptake value (SUV) alone, as inflammatory lesions have shown to have a very high SUV, and in some cases both can co-exist. In such doubtful cases, dual time PET-CT (3-5 h delayed) is of paramount importance in confidently differentiating inflammatory/infective from a malignant cause.

Asymmetric synthesis of γ-aryl-substituted GABA derivatives via a highly diastereoselective Rh-catalyzed boronic acid addition at room temperature

A highly diastereoselective Rh-catalyzed boronic acid addition to enantiopure sulfinylimines at room temperature providing γ-aryl GABA derivatives has been described.

Facile synthesis of 1-trifluoromethylalkenes via the decarboxylation of α-trifluoromethyl-β-lactones

DCC-mediated cyclodehydration of α-trifluoromethyl-β-hydroxy acids provides α-trifluoromethylated β-lactone intermediates, without loss of stereoselectivity. These lactones undergo facile decarboxylation providing a simple route to obtain both alkyl and aryl 1-trifluoromethyl alkenes in excellent yields and stereoselectivity.

In celebration of the 80th birthday of Professor Ei-ichi Negishi

Photo credit © Steve Scherer, Purdue University.

Ammonia-mediated, large-scale synthesis of ammonia borane

The presence of NH₃ allows a high concentration, ambient temperature synthesis of ammonia borane from sodium borohydride in air using reagent-grade THF.

Diastereoselective synthesis of α-(aminomethyl)-γ-butyrolactones via a catalyst-free aminolactonization

An auto-catalytic domino reaction involving an aza-Michael reaction, proton transfer, and lactonization furnishing α-aminomethyl-γ-butyrolactones in near quantitative yields and excellent diastereoselectivity is described.

Synthetic α-(aminomethyl)-γ-butyrolactones and their anti-pancreatic cancer activities

Aminated α-methylene-γ-butyrolactones, which are readily synthesized with facile control of the diastereoisomerism, provide an economical and commercially-viable alternative to the use of aminated natural products. These aminoloactones, which exhibit excellent activity against three pancreatic cancer cell lines when measured at 10 μM-Panc-1, MIA PaCa-2, and BxPC-3-and are comparable to or better than parthenolide and dimethylaminoparthenolide (DMAPT, LC-1). It has also been shown that there is an effect on the biological activity depending on the identity of the amine.

Enantioselective synthesis of anti- and syn-β-hydroxy-α-phenyl carboxylates via boron-mediated asymmetric aldol reaction

A reagent-controlled, diastereo- and enantioselective synthesis of anti- and syn-β-hydroxy-α-phenyl carboxylates has been achieved by the proper choice of solvent, temperature, alkoxy group, and amine for the diisopinocampheylboron-mediated asymmetric enolization-aldolization of phenylacetates. The pure diastereomers can be readily separated by column chromatography.