Regioselective SNAr reactions of substituted difluorobenzene derivatives: practical synthesis of fluoroaryl ethers and substituted resorcinols

In this Letter, we describe a practical and highly selective method for the preparation of fluoroaryl ethers and differentially substituted resorcinol derivatives. This synthetic strategy relies on a selective S_NAr of substituted difluorobenzene derivatives with various alcohols.     

Regioselective synthesis of 1,3,5- and 1,3,4,5-substituted pyrazoles via acylation of N-Boc-N-substituted hydrazones

Acylation of N-Boc-N-methylhydrazones followed by TFA treatment affords regioselective access to substituted pyrazoles. Both regioisomers of 1-methyl-3,5-disubstituted-1H-pyrazoles can be selectively obtained. This procedure can also be employed for the regioselective preparation of fully substituted 1H-pyrazoles.     

Synthesis of cyclopropanoid analogues of N-acyl-muramyldipeptide as potential immunostimulants

The preparation of diastereomerically pure cyclopropanoid muramyldipeptide analogues from suitable substituted cyclopropylamines is described.     

Specific syntheses and electrochemistry of isomeric [Mn(CO)6-n(CNMe)n] (n = 3, 4) complexes

1'1,-Ferrocenediacetic acid anhydride has been prepared and it has been shown to be useful in the preparation of new heteroannularly substituted ferrocenyl-penicillins and -cephalosporins; these compounds exhibit antibiotic activity.     

A facile protocol for the preparation of 5-alkylidene and 5-imino substituted hydantoins from N,N′-disubstituted parabanic acids

A convenient procedure for the preparation of various substituted (thio)hydantoins is described. The method is based on Wittig and aza-Wittig reactions of parabanic acids with phosphonium ylides. The reactions occurred both regio- and stereo-selectively.     

Mono C-alkylation and mono C-benzylation of barbituric acids through zinc/acid reduction of acyl, benzylidene, and alkylidene barbiturate intermediates

Through systematic exploration of reaction conditions, very efficient preparative procedures for obtaining large quantities of substituted 5-alkyl and 5-benzylbarbituric acids were developed. The procedure involves a two step preparation in which the second step is zinc dust/acid reduction. For preparation of 5-alkylbarbiturates, the first step is the preparation of either 5-acyl or 5-alkylidenebarbiturate. If 5-benzylbarbiturate is the target product, then the first step includes the preparation of 5-benzylidene. Regardless of the nature of the first step, all reactions presented synthetic yields around 90% and isolation and purification involves only crystallization.     

Synthesis of cyclopropanoid 2-epi-muramyldipeptide analogues as potential immunostimulants

The preparation of cyclopropanoid 2-epi-muramyldipeptide analogues from suitable substituted cyclopropylamines is described.     

Synthesis of substituted [1,3]thiazolo[4,5-b]pyridines and [1,3]thiazolo[4,5-d][1,2,3]triazines

In this work, we described an easy preparation of substituted 4-amino-5-cyano-1,3-thiazoles. These compounds have been used as starting materials to obtain two classes of compounds. New substituted [1,3]thiazolo[4,5-e]pyridines were synthesized in one step via Friedländer reaction. Diazotation of 4-amino-5-cyano-1,3-thiazoles afforded 4-chloro[1,3]thiazolo[4,5-d][1,2,3]triazines in one step. The later was substituted by a secondary amine to obtain substituted 4-amino[1,3]thiazolo[4,5-d][1,2,3]triazines.     

Unprecedented N(H)-bridged tetraaza[1.1.1.1]m,p,m,p-cyclophanes

The first uncatalyzed preparation of tetraaza[1.1.1.1]m,p,m,p-cyclophanes (symmetrical and unsymmetrical) gave access to previously unknown N(H)-bridged derivatives that could be further substituted. NMR studies and theoretical calculations show that these macrocycles adopt an 1,3-alternated conformation.     

An improved synthesis of N-aryl and N-heteroaryl substituted piperidones

An efficient Pd(0)-catalyzed protocol for the rapid and efficient preparation of N-aryl and N-heteroaryl substituted piperidones is described. The two step syntheses proceed with an overall yield of 50-70% using X-Phos as optimal ligand for the Pd(0)-catalyzed Buchwald-Hartwig amination followed by subsequent hydrolysis of resulted ketals.     

AlCl3 induced C-N bond formation followed by Pd/C-Cu mediated coupling-cyclization strategy: synthesis of pyrrolo[2,3-b]quinoxalines as anticancer agents

AlCl₃ facilitated C-N bond forming reaction between 2,3-dichloroquinoxaline and anilines affording a convenient method for the preparation of N-aryl substituted 3-chloroquinoxalin-2-amines. A related N-benzyl derivative, however, was prepared via a conventional method. These N-alkyl/aryl substituted 3-chloroquinoxalin-2-amines on coupling with terminal alkynes in toluene under Pd/C-Cu catalysis afforded a range of 1,2-disubstituted pyrrolo[2,3-b]quinoxalines within 3-5 h in good to excellent yields. Some of the compounds synthesized showed promising anti-proliferative properties when tested in vitro against two cancer cell lines. Docking studies indicated that these molecules interact well with human Akt in silico.     

Highly substituted 2,3,7,8,12,13,17,18-octaethylporphyrins with meso aryl residues

Highly substituted porphyrin-bearing meso aryl groups are useful compounds for optical applications and for studies on the interrelationship between the substituent pattern, macrocycle conformation and physical properties. They serve as biomimetic models for the function of tetrapyrroles in nature and help to elucidate modulation of cofactor properties through conformational effects. Using a sequence of lithium organic substitution reactions the synthesis of novel free base 5,10-A₂- and 5,10-AB-2,3,7,8,12,13,17,18-octaethylporphyrins bearing donating groups such as -OMe and -NMe₂ on the aryl-substituent was achieved. Larger aromatic residues (1-naphthyl, 9-anthracenyl and 9-phenanthrenyl) could be introduced into the macrocycle system as well, and these systems were used for the preparation of highly substituted porphyrins with a mixed substituent pattern. Using phenanthrenyl derivatives, the complete series of meso phenanthrenyl substituted octaethylporphyrins was successfully synthesized and the palladium complexes were prepared for photophysical investigations. Structural studies clearly showed the influence of individual substituents on the conformation of the tetrapyrrole macrocycle and conformational analyses revealed the variation of the underlying distortion modes depending on the type and arrangement of the meso substituents.     

环四甲撑四硝胺/1,3,5-三氨基-2,4,6-三硝基苯共晶炸药的分子模拟研究

构建环四甲撑四硝胺 (HMX) /1,3,5-三氨基-2,4,6三硝基苯 (TATB)不同的共晶结构模型,用分子动力学(MD)模拟得到其平衡结构。基于平衡结构进行X射线粉末衍射（XRD）图谱模拟和能量计算。结果表明,与纯组分相比,HMX/TATB共晶结构的X射线粉末衍射图与主成分HMX相似,并均有新峰出现;TATB在HMX表面自由能最高、生长速率最慢的 (0 1 1) 晶面上发生取代后的能量最低,结构最稳定,据此推测在制备HMX/TATB共晶炸药过程中,TATB分子更容易进入HMX自由能高的晶面,得到结构稳定的共晶而使HMX变得更为钝感。     

New approaches to the synthesis of pyridinium N-heteroarylaminides

Different substituted pyridinium N-heteroarylaminides have been prepared in one step from N-aminopyridinium iodide and the corresponding heteroaryl halide by two alternative routes. The use of Pd catalysis allowed the easy preparation of products from the less reactive haloheterocycles. The use of water as a solvent in conjunction with microwave heating dramatically diminishes the reaction time without having an adverse effect on reaction yields.     

An improved procedure for the preparation of 2-amino-8-alkylpyrido-[2,3-d]pyrimidin-4(3H)-ones (8-alkyl-N5-deazapterins)

We report an improved procedure for the preparation of 8-alkyl-N5-deazapterins which allows clean preparation of all ring-methyl substituted compounds, including 5- and 7-methyl substituted compounds. The procedure was also successfully applied to the preparation of N5-deazapterins with improved yield over previous reports. The uv/visible and pKa data confirm the predicted increased basicity of 8-alkyl-N5-deazapterins compared with the N5-deazapterin parents, and indicate that N5-deazapterins protonate on N8 and 8-alkyl-N5-deazapterins protonate on N3.     

A concise synthesis of asymmetrical N,N′-disubstituted guanidines

We present a new and concise method for the preparation of asymmetrical N,N′-disubstituted guanidines starting from thiourea via the reaction of N-Boc-protected N′-alkyl/aryl substituted thioureas with an amine in the presence of mercury(II) chloride and triethylamine.     

An efficient route to 5-(hetero)aryl-2,4′- and 2,2′-bipyridines through readily available 3-pyridyl-1,2,4-triazines

A new route to substituted bipyridines based on a new method for the synthesis of substituted 3-pyridyl-1,2,4-triazines and their aza-Diels-Alder reactions is shown to be an efficient strategy for the preparation of structurally diverse bipyridine ligands.     

Facile preparation of bicyclo[2.2.2]octenone derivatives via Diels-Alder cycloadditions of in situ-generated masked o-benzoquinones

Diels-Alder cycloadditions of in situ-generated, substituted 2,2-dimethoxycyclohexa-3,5-dienones with olefinic dienophiles resulted in the development of an efficient method for the preparation of highly functionalized bicyclo[2.2.2]oct-5-en-2-ones with good to excellent yields.     

Regioselective synthesis of syn disubstituted dibenzo-30-crown-10 ethers

A practical and regioselective synthetic method for the synthesis of syn substituted dibenzo-30-crown-10 ethers is reported. This novel methodology is reported with the syntheses of dibenzo crown ethers bearing nitro, formyl and carbomethoxy groups. The synthesis of macrocyclization precursors was accomplished in three steps and featured an application of para-methoxybenzyl group (PMB) as protecting group of phenol moiety that is orthogonal to NO₂, CHO and COOMe groups. General non-high dilution macrocyclization conditions have been developed that allow for the effective preparation of substituted large crown ethers.     

New method of preparation of C2F5Li and its reactions with cyclic imines and lactims: Synthesis of α-pentafluoroethyl proline

Addition of pentafluoroethyllithium to cyclic imines leads to pentafluoroethyl substituted pyrrolidines, piperidines and azepanes while reaction of cyclic lactims gives rise to 2-pentafluoroethyl imines. Oxidative cleavage of 2-furyl-2-pentafluoroethyl pyrrolidine has been found to be an effective method for the preparation of a racemic α-pentafluoroethyl proline.