Reaction of tert-butyl isocyanide and dialkyl acetylenedicarboxylates in the presence of 2-acetylbutyrolactone. Synthesis of functionalized α-methylene-γ-butyrolactones

Reaction of tert-butyl isocyanide with dialkyl acetylenedicarboxylates in the presence of 2-acetylbutyrolactone leads to the formation of dialkyl (E)-2-{(tert-butylamino)[2-oxo-4,5-dihydro-3(2H)-furanylidene]methyl}-2-butenedioates.     

A simple approach to the synthesis of dialkyl 5-tert-butylamino-[2,2′]bifuranyl-3,4-dicarboxylates

Reaction of tert-butyl isocyanide with electron-deficient acetylenic esters in the presence of N¹-[(Z)-1-benzoyl-3-oxo-3-phenyl-1-propenyl]-2-(2-furyl)-2-oxoacetamide leads to dialkyl 5-tert-butylamino-[2,2′]bifuranyl-3,4-dicarboxylates in moderate yields.     

Reaction between tert-butyl isocyanide, dialkyl acetylenedicarboxylates, and aromatic carboxylic acids: an efficient method for the synthesis of dialkyl (E)-2-{[benzoyl(tert-butyl)amino]carbonyl}-2-butenedioate derivatives

Protonation of the reactive intermediates produced in the reaction between tert-butyl isocyanide and dialkyl acetylenedicarboxylates by aromatic carboxylic acids leads to vinylnitrilium cations, which undergo nucleophilic reaction with conjugate bases of the carboxylic acids to produce dialkyl (E)-2-[(benzoyloxy)(tert-butylimino)methyl]-2-butenedioates and this intermediate rearranges to the dialkyl (E)-2-{[benzoyl(tert-butyl)amino]carbonyl}-2-butenedioate derivatives.     

Interaction of 3,5-di-tert-butyl-o-benzoquinone with secondary amines—a pathway to new sterically hindered N,N-disubstituted o-aminophenols

The interaction of 3,5-di-tert-butyl-o-benzoquinone with secondary amines has been studied. The synthetic procedure was developed in order to synthesize a series of new N,N-disubstituted o-aminophenols. The interaction of 3,5-di-tert-butyl-o-benzoquinone with dimethylamine leads to 2-(N,N-dimethylamino)-4,6-di-tert-butyl-phenol, which is oxidized in the reaction medium by the parent 3,5-di-tert-butyl-o-benzoquinone forming spirocompound 4,5′,6,7′-tetra-tert-butyl-3′-methyl-3′H-spiro[1,3-benzodioxol-2,2′-[1,3]benzoxazole].     

A simple and efficient approach to the synthesis of highly functionalized fused benzochromenes

Protonation of the reactive intermediates produced in the reaction between tert-butyl isocyanide and dimethyl acetylenedicarboxylate or dibenzoylacetylene, by 1-naphthol, 2-naphthol, 2,3-dihydroxynaphthalene, 2,7-dihydroxynaphthalene or 4-methyl-8-hydroxycoumarin leads to vinylnitrilium cations, which undergo carbon-centered Michael type addition with the conjugate base of the naphthols to produce highly functionalized benzochromenes.     

Complexes of technetium(I) (Tc, Tc) pentacarbonyl core with π-acceptor ligands (tert-butyl isocyanide and triphenylphosphine): Crystal structures of [Tc(CO)5(PPh3)]OTf and [Tc(CO)5(CNC(CH3)3)]ClO4

A procedure was developed for preparing [^99mTcX(CO)₅] (X = Cl, Br, I) in a reasonable yield by high-pressure carbonylation with CO of ^99mTcO₄⁻ in aqueous solutions. In the synthesis, the substantial part of the target product is accumulated in the gas phase and can be transferred from the autoclave into various solvents when relieving the pressure. Compounds [^99mTcX(CO)₅] (X = Cl⁻, Br⁻, I⁻) are stable in solutions for several hours, but in the course of longer storage they gradually decompose to give the tricarbonyl species. Substitution of the halide ligands in [⁹⁹TcX(CO)₅] and [^99mTcX(CO)₅] with tert-butyl isocyanide and triphenylphosphine was studied. The structures of the complexes [Tc(CO)₅(PPh₃)]OTf and [Tc(CO)₅(CNC(CH₃)₃)]ClO₄ are presented.     

Di-tert-butyl dicarbonate: a versatile carboxylating reagent

Carbon nucleophiles generated by a non-nucleophilic base (LDA) were effectively trapped with di-tert-butyl dicarbonate (Boc-anhydride) to provide the corresponding tert-butyl aryl acetates, di-tert-butyl aryl malonates, unsymmetrical aryl malonates and tert-butyl benzoates in high yields. This reaction represents another useful way to prepare a variety of tert-butyl carboxylates and highlights the synthetic utility of di-tert-butyl dicarbonate as a versatile carboxylating reagent.     

One-pot asymmetric synthesis of α-trifluoromethylated amines from α-trifluoromethyl ketones

Diastereoselective reduction of (Rs)-N-tert-butanesulfinyl α-trifluoromethyl ketimines formed in situ from the corresponding α-trifluoromethyl ketones and N-tert-butanesulfinamide has been achieved, and either diastereomer of N-tert-butanesulfinyl α-trifluoromethyl amines was obtained in good yields with excellent diastereoselectivities (up to 99:1 dr) using NaBH₄ and L-Selectride as the reductants, respectively.     

An effective C-C double bond formation via Cu(I)-catalyzed dehydrogenation

A dehydrogenation method using Cu(I) and either N,N-di-tert-butylthiadiaziridine 1,1-dioxide or N,N-di-tert-butyldiaziridinone is reported. The dehydrogenation allows a facile introduction of C-C double bond(s) into various carbocycles and heterocycles such as oxazolines and thiazolines.     

An efficient method for the conversion of aromatic and aliphatic nitriles to the corresponding N-tert-butyl amides: a modified Ritter reaction

Aromatic and aliphatic nitriles react with tert-butyl acetate in the presence of a catalytic amount of sulfuric acid to give the corresponding N-tert-butyl amides in excellent yields.     

Condensations of N-arylhydroxylamines for the preparation of 5,5′-di-tert-butyl-2,2′-dihydroxydiphenylamine

Acid-promoted condensation of 4-tert-butyl-2-hydroxylaminoanisole with p-tert-butylphenol resulted in the formation of 5,5′-di-tert-butyl-2,2′-dihydroxydiphenylamine upon demethylation with BBr₃. Protection of the acidic phenol unit was required to isolate the acid labile N-arylhydroxylamine intermediate.     

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.     

Stable axial-rich chair conformer of myo-inositol derivatives due to introduction of two adjacent bulky silyl protections

The ring-conformational change of myo-inositol derivatives by introducing two tert-butyldimethylsilyl, triisopropylsilyl, or tert-butyldiphenylsilyl groups into the 1,2-trans hydroxy groups--3,4- and 4,5-positions--were investigated. The cyclohexane cores of the 4,5-bis-O-silylated derivatives with tert-butyldiphenylsilyl or triisopropylsilyl groups were present in the axial-rich chair form.     

Synthesis of modified Weinreb amides: N-tert-butoxy-N-methylamides as effective acylating agents

An efficient preparation of N-methyl-O-tert-butylhydroxylamine hydrochloride has been settled, which allowed the synthesis of modified Weinreb amides. Nucleophilic addition of organolithium and Grignard reagents on these N-tert-butoxy-N-methylamides afforded efficiently the corresponding ketones and reduction with DIBAL furnished the corresponding aldehydes in good yields up to 97%.     

Efficient preparation of Ellman’s imines from trifluoromethyl ketones promoted by zirconium(IV) tert-butoxide

An efficient synthesis of chiral N-tert-butanesulfinyl trifluoromethyl ketimines by using zirconium(IV) tert-butoxide is described. Compared to conventional titanium(IV) ethoxide, this protocol gave better result especially for sterically hindered ketones. In addition to the high reactivity, a high degree of enantiopurity of the N-tert-butanesulfinyl group is retained.     

Boron trichloride as an efficient and selective agent for deprotection of tert-butyl aryl sulfonamides

A fast, mild and selective method for deprotection of tert-butyl aryl sulfonamides utilizing BCl₃ as deprotection reagent has been developed. A variety of tert-butyl aryl sulfonamides used under these conditions gave the corresponding primary sulfonamides in high yields. The method does not cleave methoxy groups and prevents incorporation of tert-butyl groups onto electron-rich aromatic rings.     

Endo- and exocyclic N-alkylation of 1- and 5-aminotetrazoles with t-BuOH-HClO4: synthesis of mono-, di-, and tri-tert-butyl substituted aminotetrazolium salts

A new method for the synthesis of 1,3,5-trisubstituted aminotetrazolium salts based on alkylation of 1- and 5-aminotetrazoles with the t-BuOH-HClO₄ system is presented. Depending on the structure of the tetrazole substrate and reaction conditions, alkylation proceeds at the endocyclic nitrogen atoms as well as at the 1- and 5-amino groups giving mono-, di-, and tri-tert-butyl substituted tetrazolium salts. An X-ray diffraction investigation of 3-tert-butyl-1,5-bis(tert-butylamino)tetrazolium perchlorate and 5-amino-1,3-di-tert-butyltetrazolium chloride was carried out.     

Trimethyl borate-induced one-pot homologation reactions of isoquinoline with di-tert-butyl-TMP zincate

Novel one-pot homologation reactions of isoquinoline and quinoline with di-tert-butyl-TMP zincate/trimethyl borate are described. 1-tert-Butyl-3,4-dihydroisoquinoline 1 and 1-tert-butylisoquinoline 2 are formed unexpectedly under the presented reaction conditions with relative ease. A reaction mechanism, including 1,2-migration of the tert-butyl group from 1-isoquinolylzincate, is proposed in detail. Migratory aptitudes of other ligands of isoquinolyl zincates are also discussed.     

Simple and mild esterification of N-protected amino acids with nearly equimolar amounts of alcohols using 1-tert-butoxy-2-tert-butoxycarbonyl-1,2-dihydroisoquinoline

A very mild, one-step esterification using nearly equimolar amounts of N-protected amino acids and alcohols, in conjunction with 1-tert-butoxy-2-tert-butoxycarbonyl-1,2-dihydroisoquinoline (BBDI) as a novel condensing reagent is described.     

Enantioselective synthesis of d- and l-α-methylcysteine with hydantoinase

A scalable and cost-effective synthesis of d- and l-α-methylcysteine is described. A key step is d-selective cyclization of N-carbamoyl S-tert-butyl-d,l-α-methylcysteine catalyzed by hydantoinase. d-5-tert-Butylthiomethyl-5-methylhydantoin and N-carbamoyl S-tert-butyl-l-α-methylcysteine were obtained with excellent yield and optical purity, and these compounds were easily separated by filtration. After hydrolysis and cleavage of the tert-butyl group, d- and l-α-methylcysteine hydrochloride were obtained.