TiF-mediated, one-pot, reductive amination of carboxylic acids with borane-ammonia.

A facile one-pot, two-step, reductive alkylation of amines with carboxylic acids has been achieved with BH-NH as an air- and moisture-stable reductant in the presence of TiF. The catalyst is effective for both amidation and reduction steps, and the product amines are isolated in high yields as either the free amines, for those products containing an arylamine, or the borane-complexes. The free amine can be separated from these complexes using BF-EtO, followed by hydrolysis.

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 TiCl, 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, ) or for stoichiometric addition of more valuable nucleophiles including furans, thiophenes, and benzodioxoles.

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.

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, BH-NH, and the catalyst, TiCl. 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 BF-EtO as the catalyst alters the reaction pathway, reducing the esters to alcohols.

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.

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 TiCl. The process, which is tolerant of a variety of potentially reactive functional groups, including -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.

TiCl-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 (TiCl) 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.

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.

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

A highly versatile synthesis of amine-boranes carbonyl reduction by sodium borohydride is described. Unlike the prior bicarbonate-mediated protocol, which proceeds a salt metathesis reaction, the carbon dioxide-mediated synthesis proceeds 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.

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. 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.

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.

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.

Stain removal effect of novel papain- and bromelain-containing gels applied to enamel.

Objectives: The aims of the study are to prepare novel stain removal gel-based formulations containing papain or bromelain and to investigate their stain removal effect when applied to enamel.

Materials And Methods: Experimental bromelain- and papain-based stain removal gels were prepared. Next, enamel/dentin tooth samples (6 × 6 mm, 4 mm in thickness) were obtained from bovine teeth, stained in coffee solution for 1 week, and measured with a digital spectrophotometer (Easyshade, Vita Zahnfabrik) for color assessment (baseline).