Amidation through carbamates

N-Alkyl carbamates of primary amines are easily converted into amides under treatment with Grignard reagents. Consequently, primary amines can be converted into amides in a one-pot reaction through carbamate protection and Grignard addition.     

Mild and selective deprotection of carbamates with Bu4NF

A new mild method allowing the removal of carbamates using TBAF in THF is reported. Reactions were performed on indole, indoline, N-methyl aniline, aniline and tryptamine derivatives. The observed selectivity according to the carbamates or the substrates is discussed. A mechanism is postulated.     

Efficient synthesis of chiral phenethylamines: preparation, asymmetric hydrogenation, and mild deprotection of ene-trifluoroacetamides

A mild and efficient route to enantioenriched aryl alkyl amines from ketones has been developed. The first successful synthesis and asymmetric hydrogenation of ene-trifluoroamides from oximes gave highly enantioenriched trifluoroacetamides (94-98% ee). The corresponding phenethyl amides are liberated under mild conditions (K₂CO₃, MeOH/H₂O). In addition, a new application of Josiphos ligands toward the asymmetric hydrogenation of both ene-acetamides and ene-trifluoroacetamides was discovered.     

DDQ mediated regiospecific protection of primary alcohol and deprotection under neutral conditions: Application of new p-methoxy benzyl-pixyl ether as reagent of choice for nucleoside protection

A simple and efficient protocol is described for regiosepecific protection of primary hydroxyl group both in nucleosides and other molecules with p-methoxy-benzyl 2,7-dimethyl pixylether (MBDPE) in presence of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Furthermore, swift deprotection of 2, 7-dimethylpixyl (DMPx) is accomplished with DDQ in MeOH. Both procedures are successfully implemented on gram-scale synthesis of modified nucleosides. This protocol offers mild and neutral conditions for selective protection and deprotection of DMPx group while compatible in presence of other conventional protecting groups such as benzoyl, benzyl, THP, TBDPS and acetonide.     

H5IO6/KI: A New Combination Reagent for Iodination of Aromatic Amines,and Trimethylsilylation of Alcohols and Phenols through in situ Generation of Iodine under Mild Conditions

A simple method for the in situ generation of iodine using H₅IO₆/KI has been developed, and its application in silylation of OH group and iodination of aromatic amines is described.     

Gas chromatographic determination of aromatic amines in water samples after solid-phase extraction and derivatization with iodine: I. Derivatization

A new method for the selective determination of aromatic amines is presented, which is based on the solid-phase extraction at pH 9 and subsequent derivatization of the analytes to the corresponding iodobenzenes. These can selectively and sensitively be determined with gas chromatography and electron-capture detection. Separation of at least 30 compounds in a single chromatographic run in 30 min is possible. With this method, 56 aromatic amines were investigated, and only in six cases no derivatives were obtained. Limits of quantitation were between 0.5 and 8 μg l⁻¹, but may still be lowered with higher sample volumes or different injection techniques. The application to water samples revealed the suitability for the investigation of ground, leachate and wastewater.     

A novel deprotection of trichloroacetamide

Deprotection of trichloroacetamide was carried out with Cs₂CO₃ in DMF or DMSO at 100 °C to afford an amine in good yield. A survey of the scope and limitations revealed the utility of the deprotection condition for various functionalized substrates.     

A practical preparation of diisopropyl phosphoryl protected amino acids

N-Diisopropyl phosphoryl protected amino acids can be prepared in high yield and without racemization by slow addition of sodium hypochlorite to a solution of the amino acid and diisopropylphosphite in water while carefully maintaining a constant pH via the addition of sodium hydroxide.     

A high loading sulfonic acid-functionalized ordered nanoporous silica as an efficient and recyclable catalyst for chemoselective deprotection of tert-butyldimethylsilyl ethers

A high loading sulfonic acid-functionalized ordered nanoporous silica efficiently catalyzes the deprotection of a variety of alcoholic TBDMS (tert-butyldimethylsilyl)ethers in methanol. The catalyst shows high thermal stability (up to 240 °C) and can be recovered and reused for at least seven reaction cycles without loss of reactivity. This method can be used to deprotect TBDMS ethers of alcohols in the presence of TBDMS ethers of phenols.     

Novel and Highly Effective Method for the Trimethylsilylation of Alcohols and Phenols with Hexamethyldisilazane (HMDS), Catalyzed by I2 Generated in situ Using Fe(NO3)3⋅9 H2O/NaI under Heterogeneous and Neutral Conditions

Structurally diverse alcohols and phenols were trimethylsilylated in a clean and efficient reaction with hexamethyldisilazane (HMDS) based on the use of I₂ generated in situ from Fe(NO₃)₃?9 H₂O/NaI. The reaction occurs very rapid in good‐to‐high yield in CH₂Cl₂ at room temperature, and the use of toxic and corrosive molecular I₂ is avoided.     

Preparation of substituted semicarbazides from corresponding amines and hydrazines via phenyl carbamates

A simple synthetic procedure for the conversion of amines and hydrazines into substituted semicarbazides was developed. The initial condensation between the desired amine and phenyl chloroformate into phenyl carbamate is followed by the addition of hydrazine under basic conditions. The reaction is tolerable to a variety of functional groups, with mild conditions and high percent yields.     

β-Tosylethylazide: a useful synthon for preparation of N-protected 1,2,3-triazoles via click chemistry

β-Tosylethylazide (TSE-N₃), which can be prepared in one step from p-tolyl vinyl sulfone and sodium azide/H₂SO₄, undergoes metal-catalyzed 1,3-dipolar cycloadditions with alkynes to produce TSE-protected 1,2,3-triazoles. The protecting group can be removed using potassium tert-butoxide in THF at −78 to 0 °C.     

3,3-Dimethoxypropylsulfonyl Group: A new versatile protecting and activating group for amine synthesis

3,3-Dimethoxypropylsulfonyl (Dimps) chloride was prepared and used as a new versatile sulfonating agent for ammonia, primary and secondary amines to afford corresponding Dimps-amides in excellent yields. The resulting N-nonsubstituted and N-monosubstituted Dimps-amides, activated amines, were alkylated satisfactorily under new Mitsunobu conditions. The Dimps group was removed by treatment in aqueous solution under acidic followed by basic conditions. Furthermore, epilachnene, the defensive droplets from the Mexican bean beetle, Epilachna varivestis, was synthesized utilizing this Dimps methodology in short steps.     

Dimethylsulfoxide-iodine catalysed deprotection of allyl carboxylic esters

A convenient method for deprotection of allyl carboxylic esters has been developed by using the inexpensive and environmentally friendly reagent dimethylsulfoxide-iodine. A variety of carboxylic esters were deprotected to the carboxylic acids. This method is more efficient and operationally simple in comparison to methods using transition metal complexes.     

N-Iodosuccinimide (NIS) as a mild and highly chemoselective catalyst for deprotection of tert-butyldimethylsilyl ethers

A variety of alcoholic TBDMS (t-butyldimethylsilyl) ethers are easily removed in excellent yields by treatment with a catalytic amount of N-iodosuccinimide (NIS, 5 mol %) in methanol. This method is able to deprotect TBDMS ethers of alcohols in the presence of TBDMS ethers of phenols.     

Tris(pentafluorophenyl)borane catalyzed Ferrier azaglycosylation with sulfonamides and carbamates

The reaction of tri-O-acetyl-d-glucal with different nitrogen nucleophiles was effectively promoted by a catalytic amount of tris(pentafluorophenyl)borane for the first time in acetonitrile at room temperature to produce a variety of azapseudoglycals via Ferrier rearrangement in good yields and preferential anomeric selectivity.     

Off-line SFE-CZE analysis of carbamates residues in tobacco samples

Summary Determination of carbamate residues in tobacco samples was carried out by solid-liquid extraction (SLE) and supercritical-fluid extraction (SFE) methods, both developed for this purpose. The clean-up step was carried out on SPE-Florisil cartridges and the extracts analysed by capillary zone electrophoresis (CZE) with UV detection.The results were compared and SFE using CO₂-acetone showed the best results in terms of recovery and generally higher extraction power. SFE in conjunction with CZE proved suitable for carbamate residue analysis in real tobacco samples.     

Selective electrochemical deprotection of cinnamyl ethers, esters, and carbamates

Electrochemical deprotection of the cinnamyl moiety from ethers, esters, and carbamates was studied with the focus on O- versus N- selectivity as well as selectivity over allyl or benzyl systems.     

The N-vinyl group as a protection group of the preparation of 3(5)-substituted pyrazoles via bromine-lithium exchange

Treatment of 3,4,5-tribromopyrazole with 1,2-dibromoethane and triethylamine gave 3,4,5-tribromo-1-vinylpyrazole, which underwent regioselective bromine-lithium exchange at the 5-position. Subsequent addition of an electrophile gave 5-substituted 3,4-dibromo-1-vinylpyrazoles. These underwent bromine-lithium or bromine-magnesium exchange predominantly at the 4-position, with the regioselectivity between the 3- and 4-positions being influenced by the nature of the metal and the 5-substituent. The 5-substituted products were de-vinylated by mild treatment with KMnO₄ affording 3-substituted pyrazoles. Alternatively, the 1-vinyl group could be used in ring-closing metathesis. Thus, 5-allylthio-1-vinylpyrazole produced 5H-pyrazolo[5,1-b][1,3]thiazine upon treatment with Grubbs' second-generation catalyst.     

A new approach to N-protected staurosporinones

A completely regioselective synthesis of two advanced precursors to glycosidic indolopyrrolo[2,3-a]carbazole alkaloids is described.