Tert-butyl Carbamate Research Articles

ChemInform Abstract: Pd‐Catalyzed Amidation of Aryl(Het) Halides with tert‐Butyl Carbamate.

Abstract Pd-catalyzed cross-coupling reaction of tert-butyl carbamate with various aryl(Het) halides with Cs2CO3 as base in 1,4-dioxane as solvent was investigated, which resulted in the formation of the desired compounds in moderate to excellent yields.

Catalyst‐Controlled Wacker‐Type Oxidation of Protected Allylic Amines

Catalyst‐Controlled Wacker‐Type Oxidation of Protected Allylic Amines

Unexpected enantioseparation of mandelic acids and their derivatives on 1,2,3‐triazolo‐linked quinine tert‐butyl carbamate anion exchange‐type chiral stationary phase

Replacement of the flexible thioether linker for the novel, rigid 1,2,3-triazole spacer group in the course of immobilization of quinine tert-butyl carbamate onto a silica surface led to a chiral stationary phase (CSP) with enhanced enantioselectivity for the resolution of mandelic acid and derivatives thereof. These new CSPs allowed efficient resolution of a wide set of mandelic acids with α-values between 1.08 and 1.68. The high loadability of these chiral ion exchange type CSPs allows preparative separation in the milligram range on an analytical column of 100×4 mm id in a single run as it was demonstrated for 4-trifluoromethylmandelic, 2-naphthylglycolic and 3,4-methylenedioxymandelic acids. The chiral recognition process has been studied using a library of 25 diverse racemic probes. A tentative model suggests that the rigid 1,2,3-triazole group takes part in the formation of an enantioselective-binding pocket of the entire and immobilized selector moiety of the CSP. The primary interaction site is given by the ionizable quinuclidine group of the Cinchona alkaloid supported by possible π-π stabilization effects within the selector-selectand complex.

A Practical Synthesis of 4-Amino-2-(Trifluoromethyl)nicotinic Acid

A practical synthesis of 4-amino-2-(trifluoromethyl)-nicotinic acid is described. 2-(Trifluoromethyl)pyridine was lithiated using lithium 2,2,6,6-tetramethylpiperidide (LTMP) in the presence of 1,3-dimethyl-2-imidazolidinone (DMI) and followed by CO 2 quench to give the C-3 carboxylation product. Subsequent directed C-4 lithiation of carboxylation product afforded 4-iodo-2-(trifluoromethyl)nicotinic acid, which was coupled with tert-butyl carbamate under Pd-catalyzed conditions and followed by Boc deprotection to yield the title product in four steps and 50% overall yield.

Pd-catalyzed amidation of aryl(Het) halides with tert-butyl carbamate

Pd-catalyzed cross-coupling reaction of tert-butyl carbamate with various aryl(Het) halides with Cs 2CO 3 as base in 1,4-dioxane as solvent was investigated, which resulted in the formation of the desired compounds in moderate to excellent yields.

ChemInform Abstract: New Route to Optically Active Amine Derivatives: Ruthenium-Catalyzed Enantioselective Hydrogenation of Ene Carbamates.

Abstract The reaction of cyclic ketones with tert-butyl or benzyl carbamate under acidic conditions directly affords prochiral ene carbamates. Their enantioselective hydrogenation in the presence of a chiral ruthenium catalyst provides a new access to optically active carbamates easy to deprotect to the corresponding optically active amines.

Tert-Butyl N-[6-(N,N-dipropyl-carbamo-yl)-1,3-benzothia-zol-2-yl]carbamate.

The title compound C19H27N3O3S, crystallizes with two unique mol­ecules in the asymmetric unit. The benzene ring of each benzothia­zole unit carries a dipropyl­carbamoyl substituent in the 6-position and a tert-butyl carbamate unit on each thia­zole ring. In the crystal structure, inter­molecular N—H⋯N and weak C—H⋯O hydrogen bonds form centrosymmetric dimers. Additional C—H⋯O contacts construct a three-dimensional network. A very weak C—H⋯π contact is also present.

Halogen-free, low flammability polyurethanes derived from deoxybenzoin-based monomers

Two novel deoxybenzoin-containing monomers, a diisocyanate and a diol, were synthesized and used to prepare polyurethane materials and foams. 4,4′-Diaminodeoxybenzoin was prepared by Ullmann coupling of 4,4′-dibromobenzil with tert-butyl carbamate. Reduction of one of the carbonyl groups, and t-Boc deprotection, gave the aromatic diamine, which was converted to 4,4′-deoxybenzoin diisocyanate (DBDI) with triphosgene. DBDI was then used to prepare two different polyurethanes, one by reaction with 1,3-propanediol, and the other by reaction with deoxybenzoin diol. The polyurethanes obtained from these reactions displayed low heat release capacity (HRC) values relative to conventional polyurethanes prepared from 4,4′-methyldiphenyl diisocyanate (MDI) and 2,4-toluene diisocyanate (TDI). Polyurethanes prepared in this study displayed HRC values as low as ∼130 J g−1 K−1, and char yields as high as ∼40%. In addition, deoxybenzoin-based oligomers containing hydroxyl end groups were also synthesized and used to prepare polyurethane foams that displayed markedly lower HRC values, and higher char yields, than conventional polyurethane foams, which burn readily and drip. Taken together, the integration of deoxybenzoin moieties into the diisocyanate or polyol component of the polymer structure is found to lower heat release rates and reduce flammability in the absence of any added flame retardant, such as halogenated compounds that represent health and environmental hazards.

Thiomaleic Anhydride: A Convenient Building Block for the Synthesis of α-Substituted γ- and δ-Lactones through Free-Radical Addition, Nucleophilic Ring Opening, and Subsequent Thiocarboxylate Manipulation

Iodoalkyl tert-butyl carbonates and carbamates undergo clean free-radical addition to thiomaleic anhydride to give substituted thiosuccinic anhydrides in high yield on treatment with tris(trimethylsilyl)silane and a radical initiator. After removal of the tert-butyloxycarbonyl group, cyclization then affords lactones or lactams substituted in the alpha-position by a thiocarboxylic acid residue. This group is converted to amides through reaction with electron-deficient sulfonamides or to aldehydes and/or ketones by the reaction of derived thioesters with either thiophenol, an electron-deficient allyl phenyl sulfide, or phenylboronic acid.

Room-Temperature Pd-Catalyzed Amidation of Aryl Bromides Using tert-Butyl Carbamate

The scope of Pd-catalyzed synthesis of N-Boc-protected anilines from aryl bromides and commercially available tert-butyl carbamate is described. For the first time, this process can be conducted at room temperature (17-22 degrees C) using a combination of Pd(2)dba(3).CHCl(3) and a monodentate ligand, tert-butyl X-Phos. Use of sodium tert-butoxide is crucial to the success of the reaction, which proceeds in 43-83% yield.

Annulations of Enantioenriched Allenylsilanes with in Situ Generated Iminium Ions: Stereoselective Synthesis of Diverse Heterocycles

Highly enantioenriched allenylsilanes participate in Lewis acid mediated annulations with in situ generated iminium ions derived from tert-butyl carbamate and methyl carbamate to selectively form functionalized 4,5-dihydropyrroles and 4,5-dihyrooxazines, respectively. The dihydropyrrole products were further elaborated in a stereocontrolled vinylsilane terminated cyclization with in situ generated oxonium ions, resulting in pyranopyrroles.

Benzyl and tert-butyl carbamate derivatives of 1,ω-amino acids as simple yet efficient gelators

We report the synthesis and a study of the gelation properties of a series of N-protected long-chain amino acids. Especially, benzyl and tert-butyl carbamate derivatives of 11-aminoundecanoic acid in their deprotonated form can gelate polar organic solvents and water at very low concentration (less than 5 mM). This is explained by the contribution of multiple forces—H-bond, van der Waals and ionic interactions—in the gel aggregate formation and stabilization, which is confirmed by the experimental data. Among the series of compounds investigated, only a dimer of 11-aminoundecanoic acid is capable of gelating toluene, which stems from the increased number of hydrogen bonding sites in the main aliphatic chain.

Glycosylative transcarbamylation: efficient transformation of tert-butyl carbamates to novel glycoconjugates

Reaction of a variety of tert-butyl carbamates under glycosylation conditions gives rise to anomeric 2-deoxy-2-amino sugar carbamates in a good to excellent yields. The reaction exhibits good tolerance to several common protecting groups, and has been used to generate unnatural glycopeptide building blocks.

Two‐Step Synthesis of 3‐Aryl‐1,3‐dihydro‐2H‐imidazo[4,5‐b]pyridin‐2‐ones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Aqueous Phosphoric Acid as a Mild Reagent for Deprotection of tert-Butyl Carbamates, Esters, and Ethers

Aqueous phosphoric acid (85 wt %) is an effective, environmentally benign reagent for the deprotection of tert-butyl carbamates, tert-butyl esters, and tert-butyl ethers. The reaction conditions are mild and offer good selectivity in the presence of other acid-sensitive groups, including CBZ carbamates, azetidine, benzyl and methyl esters, TBDMS, and methyl phenyl ethers. The mildness of the reaction is further demonstrated in the synthesis of clarithromycin derivative, in which a tert-butyl ester is removed in the presence of cyclic carbamate, lactone, ketal, acetate ester, and epimerizable methyl ketone functionalities. The reaction preserves the stereochemical integrity of the substrates. The reactions are high yielding, and the workup is convenient.

Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for N- tert-butoxycarbonylation of amines under solvent-free conditions at room temperature

Commercially available copper(II) tetrafluoroborate hydrate was found to be a highly efficient catalyst for chemoselective N- tert-butoxycarbonylation of amines with di- tert-butyl dicarbonate under solvent-free conditions and at room temperature. Various aromatic amines were protected as their N- tert-butyl carbamates in high yields and in short times. No competitive side reactions such as isocyanate, urea, and N, N-di- t-Boc formation was observed. Chemoselective N- tert-butoxycarbonylation was achieved with substrates bearing OH and SH groups. Chiral α-amino acid esters afforded the corresponding N- t-Boc derivatives in excellent yields.

9-(4-Bromophenyl)-9-fluorenyl as a Safety-Catch Nitrogen Protecting Group

[reaction: see text] The 9-(4-bromophenyl)-9-fluorenyl (BrPhF) group has been developed as a novel safety-catch amine protection. This relatively acid-stable protecting group can be successfully activated by palladium-catalyzed cross-coupling reaction of the aryl bromide with morpholine and then cleaved effectively under mild conditions using dichloroacetic acid and triethylsilane. Complementary conditions are reported for selective removal of the BrPhF group in the presence of tert-butyl esters and carbamates as well as deprotection of tert-butyl esters and carbamates in the presence of BrPhF amines.

Boc-Protected Amines via a Mild and Efficient One-Pot Curtius Rearrangement

[reaction: see text] The reaction of a carboxylic acid with di-tert-butyl dicarbonate and sodium azide allowed the formation of an acyl azide intermediate, which undergoes a Curtius rearrangement in the presence of tetrabutylammonium bromide and zinc(II) triflate. The trapping of the isocyanate derivative in the reaction mixture led to the desired tert-butyl carbamate in high yields at low temperature. These reaction conditions are compatible with a variety of substrates, including malonate derivatives, which provide access to protected amino acids.

Synthesis and reactive blending of amine and anhydride end-functional polyolefins

Polyolefins having low polydispersity and containing terminal functional groups are difficult to synthesize, due to limitations in catalysis technology. We have developed methods for preparing model polyolefins with terminal amine or anhydride functionality and of controlled molecular weight and narrow polydispersity. Both 1,4- or 1,2-polybutadienes are prepared by living anionic polymerization, with introduction of a functional group precursor during chain termination. The functional groups are protected as tert-butyl carbamate and tert-butyl ester for the amine and anhydride, respectively. The polymers are hydrogenated heterogeneously, with subsequent deprotection yielding saturated polymers with functionalities of up to 90%. These materials, due to their low polydispersity, comprise a useful model system for measuring melt reaction kinetics by gel permeation chromatography. Melt blending of amine- and anhydride-functional PEE90 (polyethylethylene) with complementary functional polystyrenes quickly yields extensive amounts of block copolymer with complex, sub-micron scale morphologies. Similar fine morphologies are observed for blends of amine- and anhydride-functional PE (polyethylene) with functional polystyrene. These functional PE and PEE90 polymers can also be used as reactive compatibilizers for polyethylene and polypropylene blends, respectively. The concentration of compatibilizer required to obtain sub-micron particles, however, is as high as 20% by weight.

DYNAMICALLY VULCANIZED THERMOPLASTIC ELASTOMER BLENDS OF NATURAL RUBBER AND POLYPROPYLENE

Dynamic vulcanization of a soft grade of thermoplastic natural rubber (TPNR) was carried out using several concentrations of Hexamethylene N, N′ bis (tert-butyl peroxy carbamate) (HBTP). The blends were melt mixed in a Brabender plasticorder. The effectiveness of dynamic vulcanization was investigated using the Brabender plastograms, swelling index measurements, rheological behavior by means of a capillary rheometer, dynamic mechanical properties, and tensile testing. It was found that varying the HBTP concentration had a great influence on the rheological behavior as well as the dynamic and tensile properties of the material. The increase of HBTP dosage resulted in an increase of the extent of crosslinking and caused an increase of the elastic modulus and a reduction of the loss modulus. The ultimate tensile strength and elongation at break also increased with increasing HBTP loading. The rheograms indicated that the blends exhibit a pseudoplastic behavior.