A new efficient synthesis of isothiocyanates from amines using di-tert-butyl dicarbonate

Alkyl and aryl amines are converted smoothly to the corresponding isothiocyanates via the dithiocarbamates in good to excellent yields using di-tert-butyl dicarbonate (Boc₂O) and 1-3 mol % of DMAP or DABCO as catalyst. As most of the byproducts are volatile, the work-up involves simple evaporation of the reaction mixture.     

Facile N-tert-butoxycarbonylation of amines using La(NO3)3·6H2O as a mild and efficient catalyst under solvent-free conditions

Facile N-tert-butoxycarbonylation of amines is described by the treatment of various primary, secondary, benzylic and aryl amines with di-tert-butyl dicarbonate in the presence of catalytic amounts of La(NO₃)₃·6H₂O under solvent-free conditions at room temperature to afford N-tert-butylcarbamates in excellent yields.     

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.     

A facile method for the preparation of carbodiimides from thioureas and (Boc)2O

A concise method for the preparation of carbodiimides from thioureas using di-tert-butyl dicarbonate [(Boc)₂O] as the dehydrosulfurizative reagent has been developed. Using DMAP as the catalyst, a variety of symmetric and asymmetric 1,3-diaryl thioureas were converted into the corresponding carbodiimides efficiently in a short time.     

Preparation of N,N'-bis-tert-Butoxycarbonylthiourea

The preparation of N,N'-bis-tert-butoxycarbonylthiourea from thiourea and di-tert-butyl dicarbonate in tetrahydrofuran is described.     

Di-tert-butyl dicarbonate as an efficient coupling reagent for the immobilization of carboxylic acid moieties

We describe an efficient methodology for anchoring diverse carboxylic acids to hydroxymethylated resins using di-tert-butyl dicarbonate as coupling reagent. The reaction is equally effective for aromatic and aliphatic acids, and Fmoc-protected amino acids.     

Chemoselective acylation of monosubstituted thiacalix[4]arene with di-<Emphasis Type="Italic">tert</Emphasis>-butyl dicarbonate

Mono-, di-, and tetrasubstituted derivatives of p-tert-butylthiacalix[4]arene containing tert-butylcarbamate, tert-butylcarbonate, and tert-butyl fragments have been prepared for the first time. Depending on the reaction conditions (reagents ratio, temperature, and the presence of a base), the interaction of the monoamine derivative of p-tert-butylthiacalix[4]arene with di-tert-butyl dicarbonate can lead to the formation of mono-, di-, and tetrasubstituted products.     

A simple acylation of thiols with anhydrides

Different thiols were efficiently acylated at room temperature with different anhydrides in the presence of potassium carbonate. Chemoselective protection of thiol in the presence of hydroxy group was achieved using di-tert-butyl dicarbonate and isatoic anhydride.     

Single-step conversion of N-benzyl, N-trityl and N-diphenylmethyl amines to t-butyl carbamates using polymethylhydrosiloxane

t-Butyl carbamates were obtained efficiently in high yields from the corresponding N-benzyl, N-trityl and N-diphenylmethyl precursors in a single-step reductive transformation employing polymethylhydrosiloxane and di-t-butyl dicarbonate under Pd(OH)₂/C catalysis.     

Thioglycoluril as a highly efficient, recyclable and novel organocatalyst for N-Boc protection of amines

A simple and efficient protocol for the chemoselective mono-N-Boc protection of various structurally diverse amines with di-tert-butyl dicarbonate using thioglycoluril as the catalyst is described. The catalyst can be readily separated from the reaction products by simple filtration and recovered for reuse. No competitive side reactions, such as formation of isocyanate, urea, oxazolidinone, and N,N-di-Boc derivatives were observed.     

A scalable and expedient method of preparing diastereomerically and enantiomerically enriched pseudonorephedrine from norephedrine

Norephedrine has been efficiently converted into the corresponding diastereomer pseudonorephedrine using a three step, one-pot reaction. The three step process involves treatment of norephedrine with di-tert-butyl dicarbonate (Boc₂O); cyclization by way of mesylate formation at the alcohol; and lithium hydroxide mediated hydrolysis of the oxazolidinone. The diastereomeric purity was determined by HPLC and the enantiomeric purity was determined by optical activity measurements and chiral stationary phase HPLC analysis of the pseudonorephedrine oxazolidinone derivatives.     

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.     

New reagent for the introduction of Boc protecting group to amines: Boc-OASUD

A new reagent, tert-butyl (2,4-dioxo-3-azaspiro [5,5] undecan-3-yl) carbonate (Boc-OASUD) for the preparation of N-Boc-amino acids is described. The Boc-OASUD reacts with amino acids and their esters at room temperature in the presence of a base and gives N-Boc-amino acids and their esters in good yields and purity. Introduction of the Boc group takes place without racemization. The Boc-OASUD, being a solid and more stable, is a better alternative to di-tert-butyl dicarbonate which is low melting and has to be dispensed in plastic containers than glass because of its poor stability.     

Guanidine hydrochloride as an organocatalyst for N-Boc protection of amino groups

A simple and efficient method for the chemoselective N-Boc protection of the amine moiety in a variety of compounds is described using di-tert-butyl dicarbonate and guanidine hydrochloride as an organocatalyst in ethanol at 35-40 °C. Selective mono-N-Boc protection of diamines and chemoselective protection of hydroxylamines without formation of any side products is achieved. Amino acids and peptides are N-Boc protected efficiently in excellent yields under convenient reaction conditions.     

Preparation of two triflate precursors for <Emphasis Type="Italic">O</Emphasis>-(2-[<Superscript>18</Superscript>F] fluoroethyl)-<Emphasis Type="Italic">L</Emphasis>-tyrosine used in positron emission tomography (PET)

Two novel triflate precursors for radiolabelling of L-tyrosine in positron emission tomography (PET) for tumor imaging, O-(2-trifluoromethanesulfonyloxyethyl)-N-(tert-butoxycarbonyl)-L-tyrosine methyl ester 9a and O-(2-trifluoromethanesulfonyloxyethyl)-N-(tert-butoxycarbonyl)-L-tyrosine tert-butyl ester 9b, are synthesized. The triflate agent, 9a or 9b, is prepared by esterification of methanol or transesterification of tert-butyl acetate with L-tyrosine, protection of the amine group with di-tert-butyl dicarbonate, alkylation with chlorohydrin, and triflation with trifluoromethanesulfonic anhydride in four steps with overall yields of 30% and 15%, respectively.     

Synthesis of Homologs of 1-Isothiocyanatoadamantane

Amines of the adamantane series reacted with carbon disulfide and di-tert-butyl dicarbonate in the presence of triethylamine and a catalytic amount of 4-(dimethylamino)pyridine to give homologs of 1-isothiocyanatoadamantane in 80–86% yields. Adamantan-2-amine, 1-(adamantan-1-yl)ethanamine, and adamantan- 1-ylmethanamine turned out to be more reactive than adamantan-1-amine; in the latter case, the reaction time was twice as long.     

N-tert-Butoxycarbonylation of amines using H3PW12O40 as an efficient heterogeneous and recyclable catalyst

The commercially available heteropoly acid H₃PW₁₂O₄₀ (0.5 mol %) is a very efficient and environmentally benign catalyst for N-tert-butoxycarbonylation of amines (primary, secondary) with di-tert-butyl dicarbonate at room temperature in short reaction times (<10 min). No competitive side products such as isocyanates, ureas, N,N-di-tert-butoxycarbonyls, O-Boc and oxazolidinones were observed. Chiral α-amino alcohols and esters afforded the corresponding N-Boc derivatives chemoselectively in excellent yields.     

Dimerization of Pheophorbide <Emphasis Type="Italic">а</Emphasis> with Activated Carboxylic Group in the Reaction with Ethylenediamine

The interaction of ethylenediamine with pheophorbide a, carboxylic group of the latter being activated with di-tert-butyl dicarbonate, has been studied. Acylation of two amino groups of ethylenediamine with activated pheophorbide a and the formation of phorbine-phorbine dimer with the macrocycles bound in the dimer via amide bonding with ethylenediamine bridge have been demonstrated. It has also be found that the phorbine-phorbine dimer is formed even in large excess of ethylenediamine with respect to pheophorbide a.     

Heterocyclization reactions of azinoisocyanates. Synthesis of 2H-1,2,4-triazol-3(4H)-one derivatives

The reaction of 1-aminoethylidenehydrazones 9 with di-tert-butyl dicarbonate and 4 -dimethylaminopyridine led to the corresponding azinoisocyanates 10 , which underwent thermal rearrangement under the reaction conditions to give 4-(tert-butoxycarbonyl)-5-methyl-2H-1,2,4-triazol-3(4H)-ones 14 . However, amidrazone 17 gave 2-(2-tert-butoxycarbonyloxy-2-phenyl)ethyl-4-(tert-butoxycarbonyl)-5-methyl-2H-1,2,4-triazol-3(4H)-one 22 and N-aziridinyliminocarbamate 18 under the similar conditions.     

An exception to the normal Mitsunobu reaction with phenols; the formation of hydrazones from salicylaldehydes

The reaction of 2-hydroxybenzaldehydes with alkanols in the presence of triphenylphosphine and di-tert-butyl azodicarboxylate (DBAD), under the Mitsunobu reaction conditions, gives rise to the formation of hydrazones as the major products rather than the expected alkyl aryl ethers.