A highly chemoselective Boc protection of amines using sulfonic-acid-functionalized silica as an efficient heterogeneous recyclable catalyst

A facile and versatile method for the chemoselective Boc protection of amines has been developed by a treatment with (Boc)₂O in the presence of sulfonic-acid-functionalized silica as a catalyst. The method is general for the preparation of N-Boc derivatives of aliphatic (acyclic and cyclic), aromatic, and heteroaromatic amines; primary and secondary amines; aminols, amino-esters; and sulfonamides. The catalyst works under heterogeneous conditions and can be recycled.     

Nanocrystalline TiO2-HClO4:A novel,efficient and recyclable catalyst for the chemoselective N-Boc protection of amines under solvent-free conditions

Nanocrystalline TiO₂-HClO₄,as newly reported catalyst,has been used as an efficient and reusable catalyst for the chemoselective N-Boc protection of amines.The clean,mild acidity condition, quantitative yields of products,short reaction time and low reaction temperature are attractive features of this reaction.In practice,this method is a combination of a satisfactory synthesis and more significantly easy product isolation and purification.     

Poly(4-vinylpyridine) catalyzed chemoselective O-TMS protection of alcohols and phenols and N-Boc protection of amines

Poly(4-vinylpyridine) (PVP) acts as an efficient and reusable catalyst for the selective and efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) and N-tert-butoxycarbonylation of amines with (Boc)₂O. All reactions were performed under mild conditions in good to high yields.     

An efficient and chemoselective Brønsted acidic ionic liquid-catalyzed N-Boc protection of amines

The first report of a Brønsted acidic ionic liquid, 1-methylimidazolium tetrafluoroborate [(HMIm)BF₄], catalyzed efficient and chemoselective N-Boc protection of various amines using (Boc)₂O is presented. Optically pure amino alcohols and amino acid esters were converted efficiently to their corresponding optically pure N-Boc derivatives. The reported method is mild, solvent-free and has the advantages of both homogeneous and heterogeneous catalysis with high product yields, selectivity and ease of product separation.     

Water-driven chemoselective reaction of squarate derivatives with amino acids and peptides

Here, we report a new class of highly chemoselective reactions between squarate derivatives and the amino acid cysteine or unprotected peptides with a N-terminus cysteine that proceed most efficiently in entirely aqueous solution at neutral pH. Kinetic and structural studies reveal that the presence of hydrogen bonding in water is primarily responsible for both the high yield and fast rate of the reaction.     

Microwave-assisted chemoselective copper-catalyzed amination of o-chloro and o-bromobenzoic acids using aromatic amines under solvent free conditions

Copper-catalyzed synthesis of N-aryl anthranilic acid derivatives using effective amination of 2-chloro and 2-bromobenzoic acid under microwave irradiation is reported.Some of the advantages of this method are high chemoselectivity,short reaction times,ease of work up procedure and elimination of the need for acid protection.     

Preparation of esters of amino acids and of peptides under mild conditions

A new method for obtaining esters of N-protected amino acids and peptides from complexes of their sodium salts with 15-crown-5 that are soluble in organic solvents is proposed.A. V. Bogatskii Physicochemical Institute, Academy of Sciences of the Ukrainian SSR, Odessa. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 224–225, March–April, 1986.     

Molecular iodine-catalyzed facile procedure for N-Boc protection of amines

An efficient and practical protocol for the protection of various structurally and electronically divergent aryl and aliphatic amines using (Boc)2O in the presence of a catalytic amount of molecular iodine (10 mol %) under solvent-free conditions at ambient temperature is presented.     

An efficient and chemoselective Cbz-protection of amines using silica-sulfuric acid at room temperature

A simple, facile, and chemoselective N-benzyloxycarbonylation of amines using silica-sulfuric acid that proceeds under solvent-free conditions at room temperature has been achieved. These reactions are applicable to a wide variety of primary (aliphatic and cyclic) secondary amines, amino alcohols, and heterocyclic amines.     

Detection of amines and unprotected amino acids in aqueous conditions by formation of highly fluorescent iminium ions

Properly substituted coumarin aldehydes can be used to detect amines and amino acids under neutral, high ionic strength conditions by the formation of highly fluorescent iminium ions. The fluorescence of one sensor increases by 26-fold upon the addition of glycine. This strong florescent response is attributed to hydrogen bonding of the chromophore carbonyl by the acidic iminium proton.     

An efficient method for the N-formylation of amines under catalyst- and additive-free conditions

A simple catalyst- and additive-free method for the N-formylation of amines has been developed. The advantages of this protocol include a wide range of functional group tolerance, high efficiency and a lack of required extra promoters under mild conditions. This convenient strategy will provide a facile synthesis towards N-formamide natural products and pharmaceutical derivatives. A mechanism that involves difluorocarbene is proposed for this reaction.     

Site-specific modification of amino acids and peptides by aldehyde-alkyne-amine coupling under ambient aqueous conditions

A highly efficient method for the direct, site-specific functionalization of amino acids and peptides, under ambient conditions, is described. In aqueous, nearly solvent-free conditions, copper(I) chloride catalyzed the aldehyde-alkyne-amine (A(3)) coupling of amino acids to form dipropargylated products in moderate to excellent yields. The propargylamine functionality provides a convenient handle for further structural modifications, demonstrated by a subsequent one-pot deprotection and "click" reaction and a solution-phase peptide coupling.     

The use of Nafion-H®/NaNO2 as an efficient procedure for the chemoselective N-nitrosation of secondary amines under mild and heterogeneous conditions

A combination of Nafion-H® and sodium nitrite in the presence of wet SiO₂ was used as an effective agent for the N-nitrosation of secondary amines under mild and heterogeneous conditions in good to excellent yields.     

A highly efficient, green, rapid, and chemoselective oxidation of sulfides using hydrogen peroxide and boric acid as the catalyst under solvent-free conditions

We report boric acid as a highly efficient and eco-friendly catalyst for the selective oxidation of sulfides to sulfoxides or sulfones, in excellent yields under solvent-free conditions, using 30% hydrogen peroxide as an oxidant. Various sulfides possessing functional groups such as alcohol, ester, and aldehyde are successfully and selectively oxidized without affecting sensitive functionalities.     

Enzymatic approach to both enantiomers of N-Boc hydrophobic amino acids

Protease catalysed hydrolysis of N-Boc-amino acid esters allows us to obtain N-Boc l-acids and d-esters of amino butanoic acid, nor-leucine, nor-valine, leucine and t-leucine in excellent ee. The reaction occurs in short reaction times and high concentrations. When a biphasic system (buffer–MTBE) is employed, a strong solvent effect is observed. This method could be of significance for the preparation of d-t-leucine, for which a practical method is currently unavailable.     

An efficient heterogeneous catalytic system for chemoselective hydrogenation of unsaturated ketones in aqueous medium

A highly chemoselective and green heterogeneous catalytic system of immobilized Ru(II)–phenanthroline complexes on amino functionalised MCM-41 material for the chemoselective hydrogenation of unsaturated ketones to unsaturated alcohols is demonstrated using water as a solvent. The XRD and FTIR spectra show the highly ordered hexagonal nature of the MCM-41, even after encapsulation of the ruthenium complex. The complex retains its configuration after anchoring, as was confirmed by FTIR and UV–Vis analysis. The detailed reaction parametric effect was studied for the hydrogenation of 3-methylpent-3-en-2-one to achieve complete conversion up to >99% chemoselectivity of 3-methylpent-3-en-2-ol. The anchored heterogeneous catalysts were recycled effectively and reused five times with marginal changes in activity and selectivity. The use of water as a solvent not only afforded high activity for the hydrogenation reaction compared to organic solvents, but also afforded a green process.