Short Review on the Synthesis of Thiophene,Pyrazole, and Thiazole Derivatives

The review summarizes the synthesis of different thiophene, pyrazole, and thiazole derivatives by refluxing 9a in ethanol with a catalytic amount of TEA or leaving it in DMF containing potassium carbonate at room temperature overnight to afford the corresponding thiophene derivative 10a . In addition, cyclization of Schiff bases with thioglycollic acid in the presence of a catalytic amount of ZnCl₂ yielded novel thiophene derivatives. Condensation of 2‐substituted‐4‐methylythio semi‐carbazides 92 with carbonyl compounds under strong acidic conditions afforded 2‐thiazolines. Also, carboxylic acid reacted with 2‐thioethylamine in the presence of triphenylphosphine and triethylamine to afford 2‐thiazolines 98 .     

A Water‐Soluble Polycarbonate With Dimethylamino Pendant Groups Prepared by Enzyme‐Catalyzed Ring‐Opening Polymerization

A water‐soluble polycarbonate with dimethylamino pendant groups, poly(2‐dimethylaminotrimethylene carbonate) (PDMATC), is synthesized and characterized. First, the six‐membered carbonate monomer, 2‐dimethylaminotrimethylene carbonate (DMATC), is prepared via the cyclization reaction of 2‐(dimethylamino)propane‐1,3‐diol with triphosgene in the presence of triethylamine. Although the attempted ring‐opening polymerization (ROP) of DMATC with Sn(Oct)₂ as a catalyst fails, the ROP of DMATC is successfully carried out with Novozym‐435 as a catalyst to give water‐soluble aliphatic polycarbonate PDMATC with low cytotoxicity and good degradability.     

New Approach to 3‐Aminothiophene‐ 2‐carboxylic Acid Derivatives: Access to 5‐Aryl‐4‐(ethylsulfanyl) Compounds

Treatment of DMSO/water solutions of β‐bromo‐α‐(ethylsulfanyl)cinnamonitriles with sodium sulphide and α‐halo acetic acids derivatives followed by cyclization in a potassium carbonate/acetone/DMSO mixture gave the expected 3‐amino‐5‐aryl‐4‐(ethylsulfanyl)thiophene‐2‐carboxylic acids derivatives in fair yields.     

Synthesis of new isoxazoles derivatives attached to sugar moieties

This work reports the synthesis of isoxazoles linked to sugar derivatives in different positions of furanosidic rings, by intramolecular oxidative cyclization of α,β‐unsaturated oximes with iodine, potassium iodide and sodium hydrogen carbonate. These oximes were obtained from aldehyde‐sugar derivatives.     

Stereospecific Decarboxylative Nazarov Cyclization Mediated by Carbon Dioxide for the Preparation of Highly Substituted 2‐Cyclopentenones

Highly substituted 2‐cyclopentenones were stereospecifically and regioselectively constructed with high catalytic efficiency through Lewis‐acid catalyzed decarboxylative Nazarov cyclization of the cyclic carbonate derivative, which is prepared by reacting the propargyl alcohol with carbon dioxide in the presence of a silver catalyst. The stereochemistry of the 2‐cyclopentenone is strictly controlled by the geometry of the alkene in the starting material. This method is applicable for various substrates.     

Protonation‐Assisted Conjugate Addition of Axially Chiral Enolates: Asymmetric Synthesis of Multisubstituted β‐Lactams from α‐Amino Acids

β‐Lactams with contiguous tetra‐ and trisubstituted carbon centers were prepared in a highly enantioselective manner through 4‐exo‐trig cyclization of axially chiral enolates generated from readily available α‐amino acids. Use of a weak base (metal carbonate) in a protic solvent (EtOH) is the key to the smooth production of β‐lactams. Use of the weak base is expected to generate the axially chiral enolates in a very low concentration, which undergo intramolecular conjugate addition without suffering intermolecular side reactions. Highly strained β‐lactam enolates thus formed through reversible intramolecular conjugate addition (4‐exo‐trig cyclization) of axially chiral enolates undergo prompt protonation by EtOH in the reaction media (not during the work‐up procedure) to give β‐lactams in up to 97 % ee.     

An Efficient Synthesis and In Vitro Antibacterial Activity of Novel Spiro‐aminopyrimidones

A highly efficient one‐pot synthesis of some new spiro‐2‐aminopyrimidinones via a three‐component reaction of cyclic ketones, methylcyanoacetate or malononitrile, and guanidinium carbonate has been developed through a domino Knoevenagel/Michael/cyclization sequence. The hydrogen bonding capacity of these compounds would make these structures especially stable. Furthermore, the antibacterial study reveals that these types of compounds exhibit good antibacterial activity.     

The Thermal Instability of 2,4 and 2,6‐N‐Alkylamino‐disubstituted and 2‐N‐Alkylamino‐substituted Nitrobenzenes in Weakly Alkaline Solution: sec‐Amino Effect

We report herein the preparation of two families of secondary amines by the reactions of two equivalents of monoamines with either 2,4 or 2,6‐difluoronitrobenzenes in N,N‐dimethylacetamide in the presence of anhydrous potassium carbonate, as precursors of biologically important nitric oxide donating N‐nitrosamines. In both instances, these compounds could be prepared in quantitative yield when the reaction temperature was held below 130°C. Above this reaction temperature, an unexpected cyclization reaction between the nitro and newly formed adjacent secondary amine group leads to the formation of benzimidazole or quinoxaline rings in low yields. Reasonable reaction mechanisms for the cyclization reaction are proposed.     

Convenient and useful synthesis of N‐carboxyanhydride monomers through selective cyclization of urethane derivatives of α‐amino acids

A new convenient synthesis of N‐carboxyanhydrides (NCAs) of α‐amino acids was achieved by selective cyclization of urethane derivatives of α‐amino acids. The urethanes were readily synthesized via N‐carbamoylation of α‐amino acids by bis(4‐nitrophenyl)carbonate quantitatively. These urethanes having 4‐nitrophenoxy moiety were tolerant to air and moisture to allow their facile purification and storage. When the obtained urethanes were heated in 2‐butanone at 60 °C, they underwent the selective cyclization via intramolecular nucleophilic attack of the carboxyl moiety to the urethane moiety with releasing 4‐nitrophenol, leading to the successful formation of the corresponding NCAs. Addition of carboxylic acids remarkably stabilized the formed NCAs during the reaction, allowing their isolation in high yields. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3839–3844, 2009     

Alkali Carbonate Effects on N‐(2‐Hydroxyethyl)urea Cyclization: Application to a 2‐Imidazolidinone Scale‐Up

An imidazolidinone intermediate ( 3 ) used in the synthesis of novel HIV‐entry inhibitors was prepared on multihundred gram scales in four steps and 40% overall yield. The penultimate step in the synthesis involved regioselective N‐cyclization of N‐(2‐hydroxylethyl)urea ( 11 ) by in situ activation of the terminal hydroxyl group with p‐TsCl in the presence of base. The ratio of N‐cyclized to O‐cyclized products followed a group IA periodic trend relative to the alkali carbonate base employed. The use of Cs₂CO₃ as base effected the desired N‐cyclization with a high degree of regiocontrol (>98%).     

Synthesis of (+)-juruenolide c: use of sequential 5-exo-digonal radical cyclization, 1,5-intramolecular hydrogen transfer, and 5-endo-trigonal cyclization.

Acetylenic alcohol 10 was converted successively into silane 11 and phenylseleno carbonate 14. On treatment with Ph3SnH, the latter underwent 5-exo-digonal radical cyclization, intramolecular hydrogen transfer, and 5-endo-trigonal cyclization, yielding 15. Conversion of the lactone into the lactol benzyl ether 17, carbon-silicon bond cleavage, and regeneration of the lactone carbonyl gave (+)-juruenolide C (1).     

Stereoselective Total Synthesis of Passifloricin A

The stereoselective total synthesis of passifloricin A ( 1 ), a naturally occurring dihydropyranone with leishmanicidal and antiprotozoal activities, has been accomplished starting from protected glyceraldehyde using Maruoka asymmetric allylation, diastereoselective iodo‐carbonate cyclization, and Grubbs' olefin metathesis reactions as the key steps.     

Hg(OTf)2-Catalyzed cyclization of alkynyl tert-butylcarbonate leading to cyclic enol carbonate

Mercuric triflate was shown to be a powerful catalyst for the cyclization of alkynyl tert-butylcarbonates giving rise to cyclic enol carbonates under mild conditions. Internal alkynyl carbonate affords endo cyclization product selectively, while terminal alkynyl carbonate provides only exo cyclization product.     

Platinum‐Catalyzed Friedel–Crafts‐Type C−H Coupling–Allylic Amination Cascade to Synthesize 3,4‐Fused Tricyclic Indoles

A novel platinum‐catalyzed cascade cyclization reaction was developed by intramolecular Friedel–Crafts‐type C?H coupling of aniline derivatives with a propargyl carbonate unit‐allylic amination sequence. Treatment of various propargyl carbonates tethered to meta‐aniline derivatives with a Pt(dba)₃/DPEphos catalyst system afforded the corresponding 3,4‐fused tricyclic 3‐alkylidene indolines in 42–99 % yield, which were transformed into 3,4‐fused indole derivatives by reaction with trifluoroacetic acid. The reaction products exhibited antiproliferative activities against cancer cells, but not normal cells, revealing the potential usefulness of this reaction for medicinal chemistry.     

An improved coupling procedure for the barton‐zard pyrrole synthesis

An improved final step in the Barton‐Zard pyrrole synthesis uses inexpensive potassium carbonate as base in the coupling‐cyclization reaction of vic‐nitro‐acetates with isocyanides. In this modification the isolated yields of synthetically useful 2‐carboalkoxypyrroles ( 1a,b and 3 ) and 2‐(p‐toluenesulfonyl)pyrroles (2a,b) consistently rise to the 78‐89% range. Conversion of 2a to 5‐(p‐toluenesulfonyl)‐2‐pyrrolinone 4 is conveniently and directly achieved by reaction with 30% hydrogen peroxide in acetic acid, thus circumventing the commonly used two step procedure involving bromination followed by solvolysis.     

Further studies on the synthesis of quinazolines from 2-fluorobenzonitriles

Recently, we reported that appropriately substituted 2-fluorobenzonitriles undergo cyclization with guanidine carbonate to afford 2,4-diaminoquinazolines usually in good to excellent yield. This paper describes the preparation of a variety of new 2,4-diaminoquinazolines substituted at positions five or seven. In addition, the reactions of selected 2-fluorobenzonitriles with formamidine acetate or acetamidine acetate were examined. The results obtained demonstrate that the analogous 4-amino- and 2-methyl-4-aminoquinazolines can be prepared by this approach but that the yields are considerably lower than when guanidine carbonate is employed as the cyclization reagent.     

MOF‐promoted Three‐component Synthesis of Functionalized Pyrano[3,2‐c]chromen under Mild Conditions

A convenient and efficient route for synthesis of various derivatives of 3‐benzoyl‐4‐phenyl‐2‐(trifluoromethyl)pyrano[3,2‐c]chromen‐5(4H)‐one has been used via tandem Knoevenagel condensation–Michael addition and intramolecular cyclization sequence. These products have been synthesized in the presence of catalytic amount of metal–organic framework (MOF) and potassium carbonate as one‐pot, three‐component reaction. MOF catalyst has been separated easily with external magnet, and high purity of products has been obtained after washing with ethanol. This protocol has advantages of simplicity, mild condition, and high yield. More importantly, MOF has been easily recycled for three times.     

一种新光致变色二芳基乙烯化合物的合成、光致变色反应动力学、荧光和结构研究

The photochromic diarylethene, 1,2-bis[2-methyl-5-（3-trifluoromethylphenyl）-3-thienyl]perfluorocyclopentene （BMTTP）, was synthesized and its photochromic kinetics, fluorescence and X-ray structure were investigated. This compound underwent a photochromic reaction both in solution and the single crystalline phase. Its cyclization/cycloreversion process was determined to be zeroth/first order reaction, respectively, and this is the first report on the cyclization/cycloreversion reaction order. In addition, its fluorescence property was also discussed.     

The Reaction Studies of α‐Chloroformylarylhydrazines with Thiols,Thioureas and α‐Cyclodiketones

The reactions of α‐chloroformylarylhydrazines 1 with various types of mercaptan, thiourea and α‐cyclodiketone have been studied intensively. 1‐Arylhydrazinecarbothioates 2 were obtained via thioesterization when α‐chloroformylarylhydrazines reacted with thiols. On the other hand, compounds 3 were obtained when α‐chloroformylarylhydrazines reacted with thio‐containing heterocyclic compounds, which suggested a totally different mechanism in these types of reactions. Further studies on the reaction of α‐chloroformylarylhydrazines 1 with thiourea compounds confirmed a novel cyclization and de‐cyclization mechanism, which led to give 2‐arylhydrazinecarboximidamides 5 and 1,3,4‐thiadiazolin‐5‐ones 6 . In addition, various 1,3,4‐oxadiazines 9 were obtained by reacting α‐chloroformylarylhydrazines with α‐cyclodiketones, showing ring cyclization was involved in this type of reaction.     

Branched Oligovinylcyclopropane by Transfer to Allylic Carbonate Comonomers via Radical Ring‐Opening Polymerization

Summary: Radical copolymerization of 1,1‐bis(ethoxycarbonyl)‐2‐vinylcyclopropane (ECVCP) with allyl carbonates that contain isopropyl groups yields highly branched polyvinylcyclopropanes. The polymerizations were carried out in the presence of 2,2‐azoisobutyronitrile at 150 °C in chlorobenzene. Structural analysis of the polymers suggested that radical ring‐opening polymerization proceeded through 1,5‐ring‐opening followed by transfer to the allylic carbonate comonomers. Intra‐molecular cyclization, which yields polycyclobutane units, was also observed during the polymerization.

Synthesis of branched 1,1‐bis(ethoxycarbonyl)‐2‐vinylcyclopropane by transfer to the isopropoxy functional allyl carbonate comonomers.