Metal-free oxidative amide formation with N-hydroxysuccinimide and hypervalent iodine reagents

An oxidative amide formation using N-hydroxysuccinimide and hypervalent iodine reagents was developed. The method enables a wide range of aldehydes and amines to be coupled under mild reaction conditions providing amide in good to excellent yield. The radical species in the reaction mixture was observed for the first time using ESR measurement, and along with other mechanistic investigations, a plausible mechanism of the reaction was proposed.     

A chemoselective deoxygenation of N-oxides by sodium borohydride-Raney nickel in water

A simple and convenient protocol for deoxygenation of aliphatic and aromatic N-oxides to the corresponding amines in good to excellent yield using sodium borohydride-Raney nickel in water is reported. Other functional moieties such as alkenes, halides, ethers, and amides are unaffected under the present reaction condition.     

Rapid access to 3-(N-substituted)-aminoquinolin-2(1H)-ones using palladium-catalyzed C-N bond coupling reaction

A series of 3-(N-substituted)-aminoquinolin-2(1H)-ones have been synthesized by the palladium-catalyzed C-N coupling reaction starting from 3-bromoquinolin-2-(1H)-ones. Various nucleophiles including amines, amides, sulfonamides, carbamates and ureas have been used successfully. In all the cases, the reactions take place rapidly in 1,4-dioxane and proceed in good to excellent yield using palladium acetate as a catalyst, Xantphos as a ligand and Cs₂CO₃ as a base.     

Palladium-catalyzed arylation of N,N-dialkylhydrazines and the subsequent conversion to anilines

Palladium-catalyzed aminations of different ArBr with N,N-dialkylhydrazines are described. The reaction proceeded in moderate to excellent yield (up to 90%) with good functional groups compatibilities as cyano, ester, ketone and Boc-amine groups are all well tolerated. Several hydrazines were proved to be good coupling partners and this process provided a general method for the isosteric replacement of benzyl amines with arylhydrazines. Moreover, a method for the N-N bond cleavage of arylhydrazines was discovered, and this two-step sequence could be employed as an alternative synthesis of aniline derivatives.     

An expeditious, efficient green methodology for the Boc protection of amines and silyl protection of alcohols over tungstophosphoric acid-doped mesoporous silica

An efficient, chemoselective and eco-friendly protocol for the protection of amines as N-tert-butylcarbamate using (Boc)₂O and protection of alcohols as silyl ether using HMDS over tungstophosphoric acid/SBA15 has been developed. Solventless condition, easy work-up, short reaction time, excellent yields and reusability of the catalyst are the striking features of this methodology which can be considered to be one of the better methods for the protection of amines and alcohols.     

Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)₂O using sulfamic acid as catalyst (5 mol %) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter reaction times (1-15 min), a cost-effective catalyst, and excellent isolated yields (90-100%); it is also environmentally benign. Moreover, the combined use of ultrasound and sulfamic acid achieves a synergic effect that is especially marked in the N-Boc protection of deactivated (sterically hindered and electron-deficient) amines. The catalyst possesses distinct advantages: ease of handling, cleaner reactions, high activity, and excellent chemoselectivity.     

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.     

Efficient and rapid synthesis of 1-substituted-1H-1,2,3,4-tetrazoles in the acidic ionic liquid 1-n-butylimidazolium tetrafluoroborate

An efficient synthesis leading directly to 1-substituted-1H-1,2,3,4-tetrazoles from easily available amines and sodium azide in stoichiometric proportions using a room-temperature ionic liquid, namely, 1-n-butylimidazolium tetrafluoroborate in excellent yields is described. The inherent Brønsted acidity and high polarity of the IL results in a significant enhancement in the reaction rate.     

Gallium(III) triflate-catalyzed one-pot selective synthesis of 2,3-dihydroquinazolin-4(1H)-ones and quinazolin-4(3H)-ones

A series of 2,3-dihydroquinazolin-4(1H)-ones and quinazolin-4(3H)-ones have been synthesized in good to excellent yields and high selectivity by one-pot reaction using isatoic anhydride, ammonium acetate (or amines), and aldehydes in ethanol or in DMSO under mild conditions, respectively. The reaction was efficiently promoted by 1 mol % Ga(OTf)₃ and the catalyst could be recovered easily after the reactions and reused without evident loss of reactivity.     

Candida antarctica lipase B-catalyzed synthesis of acetamides using [BMIm(PF6)] as a reaction medium

An efficient protocol has been developed for synthesis of acetamides using Candida antarctica lipase B (CaL B) in [BMIm(PF₆)] as a greener reaction medium. The reaction is applicable to a wide variety of aliphatic esters/acetic acid and amines providing excellent yields of corresponding acetamide. The catalyst exhibits remarkable activity and is reusable for up to four consecutive cycles.     

Solvent-assisted thiocarboxylation of amines and alcohols with carbon monoxide and sulfur under mild conditions

DMSO or DMF as a solvent strongly accelerated the thiocarboxylation of amines and alcohols with carbon monoxide and sulfur. Under mild conditions (1 atm, 20 °C), this thiocarboxylation of amines assisted by DMSO with carbon monoxide and sulfur has been developed into a practical and convenient synthetic method for S-alkyl thiocarbamates in good to excellent yields, including EPTC, thiobencarb, orbencarb, and molinate (herbicides). DMF also showed the similar solvent effect. NMP slightly decreased the effect for the thiocarboxylation of amines, and the yield of S-alkyl thiocarbamate was lowered in DMAc. Surprisingly, no formation of S-alkyl thiocarbamate was observed at the use of the other solvents, such as THF, hexane, toluene, AcOEt, MeCN, MeOH, and H₂O. The present solvent-assisted thiocarboxylation with carbon monoxide and sulfur could be also applied to a new synthesis of S-alkyl O-alkyl carbonothioates from alcohols under mild conditions (1 atm, 20 °C) in DMF using DBU (1,8-diazabicyclo[5.4.0]undec-7-ene).     

A new and efficient one-pot synthesis of 2-hydroxy-1,4-dihydrobenzoxazines via a three-component Petasis reaction

The secondary amines synthesized by the reaction between 2-aminophenols and aromatic aldehydes, via the reduction of the corresponding imines, were employed in the synthesis of new 2-hydroxy-2H-1,4-benzoxazine derivatives through a one-pot Petasis multicomponent reaction in good to excellent yields.     

N,N′,N″-Tri-Boc-guanidine (TBG): a common starting material for both N-alkyl guanidines and amidinoureas

In this Letter, we describe the unexpected reaction pattern of N,N′N″-tri-Boc-guanidine (TBG) with amines at room temperature and under reflux conditions affording N-substituted guanidines and amidinoureas, potentially important compounds with extensive applications in medicinal chemistry. This investigation shows that TBG is an excellent, readily available common starting material for the synthesis of various N-alkyl guanidines as well as N-alkyl-N′-substituted amidinoureas by simply manipulating the reaction conditions.     

Catalyst-free synthesis of functionalized dihydro-2-oxypyrroles by the reaction of enaminones and N,N′-bis(phenylmethylidene)phenylmethane

A catalyst-free and convenient approach for the preparation of substituted dihydro-2-oxypyrrole is described. This three-component reaction between primary amines, dialkyl acetylenedicarboxylate, and N,N′-bis(phenylmethylidene)phenylmethane proceeds in MeOH under reflux conditions in good to excellent yields.     

Lanthanum(III) nitrate hexahydrate or p-toluenesulfonic acid catalyzed one-pot synthesis of 4(3H)-quinazolinones under solvent-free conditions

The one-pot synthesis of quinazolinone derivatives from the reaction of anthranilic acid, trialkyl orthoformate and amines in the presence of lanthanum(III) nitrate hexahydrate or p-toluenesulfonic acid has been carried out. The reaction occurred in a few minutes under solvent-free conditions and in excellent yields.     

Copper nanoparticles catalyzed N-H functionalization: An efficient solvent-free N-tert-butyloxycarbonylation strategy

A chemoselective transformation of amines to their tert-butyloxycarbonyl (Boc) protected derivatives (NBoc) is described using Cu-NPs under solvent-free conditions. Simple method, rapid reaction rate, mild conditions, tolerance of a wide range of functional groups, excellent yield, ease recovery and high catalytic turnover are the salient features of this approach. tert-Butyloxycarbonylation of chiral amino acid esters and amino alcohols were performed without racemization.     

Palladium(II)/2,2′-bipyridine-catalyzed addition of arylboronic acids to N-tosyl-arylaldimines

A Pd(II)/NO₂-bpy-catalyzed addition of the arylboronic acids to N-tosylaldimines to yield diarylmethylamines with moderate to excellent yield was developed. The use of bipyridines as the ligands is crucial in this reaction. The asymmetric version of the reaction also showed that a moderate high yield and ee value can be obtained using the pymox ligands.     

Regioselective synthesis of pyrano[3,2-f]quinoline and phenanthroline derivatives using molecular iodine

A series of polysubstituted pyrano[3,2-f]quinoline and phenanthroline derivatives have been synthesized by molecular iodine-catalyzed tandem reaction of various propargylic alcohols with or without substituted amines in excellent yields. Moreover, the cyclized side products are also pyrano[3,2-f]quinoline and phenanthroline derivatives.     

γ-Selective allylic substitution reaction with Grignard reagents catalyzed by copper N-heterocyclic carbene complexes and its application to enantioselective synthesis

The reaction of allylic compounds with alkyl Grignard reagents in the presence of a catalytic amount of copper N-heterocyclic carbene (NHC) complexes proceeded predominantly in an S_N2′ reaction pathway to give γ-substituted product in excellent yield. The method was applied to asymmetric reaction by using optically active NHC ligands.     

Efficient oxidative N-dealkylative addition of trialkylamines to dimethyl acetylenedicarboxylate using BrCCl3 as the terminal oxidant

Herein we present a continuous improvement of visible-light mediated N-dealkylative addition of tertiary amines to dimethyl acetylenedicarboxylates (DMAD) using alkyl halogenides as external oxidants together with base additives. This method is highlighted by excellent tolerance with various tertiary amines and good to excellent yields in short reaction time under mild conditions.