Total synthesis of (±)-Scrodentoid A

An efficient total synthesis of scrodentoid A was accomplished starting from a Hagemann's ester and a substituted (2-bromoethyl)benzene. Key reactions in this synthesis include C-alkylation of the Hagemann's ester, 6-endo-Trig cationic cyclization of an enone and Lewis acid promoted isomerization of a cis-fused ketone.     

Easy access to optically active Hagemann's esters

The synthesis of optically active Hagemann's esters was investigated. The starting materials in this approach were enamino esters (R,Z)-8, prepared through the condensation of keto ester 6 with (R)-1-phenylethylamine 7. Michael addition reaction of the enamino esters (R,Z)-8 with methyl vinyl ketone gave the expected adducts 10 with good e.e.s of 93–96%. Subsequent annulation of the adducts furnished optically active Hagemann's esters.     

Concise Synthesis of 2‐Arylpropanoic Acids and Study of Unprecedented Reduction of 3‐Hydroxy‐2‐arylpropenoic Acid Ethyl Ester to 2‐Arylpropenoic Acid Ethyl Ester by BH3⋅THF

We have developed a concise method of synthesizing racemic arylpropanoic acids, which have been widely used as nonsteroidal anti‐inflammatory drugs (NSAIDs). The synthesis involves only four steps from commercially available benzaldehyde. The synthesis incorporates an unprecedented reduction reaction, conversion of 3‐hydroxy‐2‐arylpropenoic acid ethyl ester to 2‐arylpropenoic acid ethyl ester by BH₃?THF. The reduction reaction has been investigated and optimized.     

Microwave‐Assisted Aqueous Synthesis of 6‐Ferrocenyl Pyridin‐2(1H)‐one Derivative

A clean and green method for synthesizing a series of new ferrocenyl pyridin‐2(1H)‐one derivative was developed via the one‐pot reactions of aldehydes, Meldrum's acid, acetylferrocene, and ammonium acetate using high‐temperature water as a solvent and microwave heating. This method had several advantages such as good yields, reduced environmental impact, and convenient procedure.     

Boron: Its Role in Energy‐Related Processes and Applications

Boron's unique position in the Periodic Table, that is, at the apex of the line separating metals and nonmetals, makes it highly versatile in chemical reactions and applications. Contemporary demand for renewable and clean energy as well as energy‐efficient products has seen boron playing key roles in energy‐related research, such as 1) activating and synthesizing energy‐rich small molecules, 2) storing chemical and electrical energy, and 3) converting electrical energy into light. These applications are fundamentally associated with boron's unique characteristics, such as its electron‐deficiency and the availability of an unoccupied p orbital, which allow the formation of a myriad of compounds with a wide range of chemical and physical properties. For example, boron's ability to achieve a full octet of electrons with four covalent bonds and a negative charge has led to the synthesis of a wide variety of borate anions of high chemical and electrochemical stability—in particular, weakly coordinating anions. This Review summarizes recent advances in the study of boron compounds for energy‐related processes and applications.     

Cationic organoiron polyelectrolyte three‐arm stars

With nucleophilic aromatic substitution and ester condensation reactions, several new first‐generation dendrimers and star‐shaped molecules containing cationic cyclopentadienyl iron moieties were prepared. Although the solubility of the organoiron star‐shaped molecules with ether bridges in polar solvents was found to decrease with an increase in the size of the molecule, the addition of ester linkages resulted in a sharp decrease in the solubility, regardless of the size. The thermal behavior of these molecules was examined with differential scanning calorimetry and thermogravimetric analysis. The glass‐transition temperatures (T_g's) of these star‐shaped molecules ranged from 123 to 170 °C. However, the addition of the ester functionality allowed for an increase in the T_g's to 151–194 °C. The star‐shaped molecules were thermally stable up to 200 °C, above which a loss of the cationic cyclopentadienyl iron moieties occurred. Degradation of the ester chains started at 321 °C, and degradation of the ether chains started at 408 °C. Electrochemical studies of the ether star‐shaped molecules showed a reduction of the 18‐electron iron centers to 19‐electron centers. This redox system was reversible at low temperatures, whereas it was irreversible at room temperature. Moreover, an increase in the number of metal moieties caused an overlap and broadening of the redox wave. Viscosity studies showed a polyelectrolyte effect for the organoiron star‐shaped molecules. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1382–1396, 2005     

New polymer syntheses. 107. Aliphatic poly(thio ester)s by ring‐opening polycondensation of 2‐stanna‐1,3‐dithiacycloalkanes

We prepared 2,2‐dibutyl‐2‐stanna‐1,3‐dithiacycloalkanes from dibutyltin oxide and α,ω‐dimercaptoalkanes. Heterocycles with five‐, six‐, seven‐, or nine‐ring members were used as bifunctional monomers for polycondensations with aliphatic dicarboxylic acid chlorides. These polycondensations conducted in bulk were highly exothermic and yielded poly(thio ester)s with number average molecular weights (M_n's) in the range of 5000–30,000 Da. These poly(thio ester)s proved to be rapidly crystallizing materials with melting temperatures in the range of 90–150 °C. In addition to the success of the new synthetic approach, two interesting and unpredictable results were obtained. All volatile species detectable by matrix assisted laser desorption induced‐time of flight (MALDI‐TOF) mass spectrometry were cyclic oligo‐ and poly(thio ester)s. Second, several polyesters showed a reversible first‐order change of the crystal modification as identified by differential scanning calorimetry measurements and X‐ray scattering with variation of the temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3656–3664, 2000     

One‐step ring‐closure procedure for 4,5‐dihydro‐1,3‐thiazino[5,4‐b]indole derivatives with Lawesson's reagent. The fifth dihydro‐1,3‐thiazino[b]indole isomer

We report a convenient approach for the synthesis of a new ring system: 4,5‐dihydro‐1,3‐thiazino[5,4‐b]indoles. The procedure involves the use of Lawesson's reagent in the presence of silica to achieve the one‐step ring‐closure reactions of 2‐benzoylamino‐3‐hydroxymethylindole intermediates to furnish 4,5‐dihydro‐2‐aryl‐1,3‐thiazino[5,4‐b]indoles. 2‐Phenylimino‐1,3‐thiazino[5,4‐b]indoles were obtained via the corresponding 3‐phenylthiourea‐2‐carboxylic acid ester derivatives by chemoselective reduction of the ester group, followed by ring closure under acidic conditions. The structures of the novel products were elucidated by IR, ¹H‐NMR, and ¹³C‐NMR spectroscopy, including 2D‐HMQC, 2D‐HMBC, and DEPT measurements. J. Heterocyclic Chem., (2011).     

pH‐ and temperature‐sensitive statistical copolymers poly[2‐(dimethylamino)ethyl methacrylate‐stat‐2‐vinylpyridine] with Functional succinimidyl‐ester chain ends synthesized by nitroxide‐mediated polymerization

Statistical copolymerizations of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) with 2‐vinylpyridine (2VP) with 80 to 99 mol % DMAEMA in the feed utilizing a succinimidyl ester‐terminated alkoxyamine unimolecular initiator (NHS‐BlocBuilder) at 80 °C in bulk were performed. The effectiveness of 2VP as a controlling comonomer is demonstrated by linear increases in number‐average molecular weight versus conversion, relatively low PDI (1.5–1.6 with up to 98% DMAEMA) and successful chain extensions with 2VP. Additional free nitroxide does not significantly improve control for the DMAEMA/2VP copolymerizations. The succinimidyl ester on the initiator permits coupling to amine‐terminated poly(propylene glycol) (PPG), yielding an effective macroinitiator for synthesizing a doubly thermo‐responsive block copolymer of PPG‐block‐P(DMAEMA/2VP). A detailed study of the thermo‐ and pH‐sensitivities of the statistical and block copolymers is also presented. The cloud point temperature of the statistical copolymers is fine tuned from 14 to 75 °C by varying polymer composition and pH. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

Tandem dynamic kinetic resolution and enzymatic polycondensation to synthesize mPEG‐functionalized poly(amine‐co‐ester)‐type chiral prodrugs

Amphiphilic poly(amine‐co‐ester)s, which contain a single effective enantiomer of an asymmetric drug and thus can avoid potentially serious side effects, are difficult to prepare through nonselective chemical routes not only in the process of introducing chiral drugs to the polymer, but also in the synthesis of the polymer's backbone by metal catalysts. A model of racemic mexiletine, an important antiarrhythmic agent, was used to demonstrate the tandem combination of Candida antarctica lipase B (CAL‐B)‐ and Pd/C‐catalyzed dynamic kinetic resolution (DKR) and subsequent CAL‐B‐catalyzed polycondensation, as an efficient protocol to prepare poly(ethylene glycol)‐functionalized poly(amine‐co‐ester)s containing (R)‐mexiletine with 99% ee value. Chemoenzymatic DKR and enzymatic polymerization conditions were optimized, and the optical purity of incorporated (R)‐mexiletine was confirmed through its hydrolysis from polyester. The copolymers can readily self‐assemble into nanometer‐scale‐sized micelles with well‐dispersed spheres, which have a size distribution that can be efficiently adjusted by changing the polymer concentration. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

New segmented poly(ester‐urethane)s from renewable resources

The physical and mechanical properties of aliphatic homopolyesters from monomers obtainable from renewable resources, namely, 1,3‐propanediol and succinic acid, were improved by their combination with aromatic urethane segments capable of establishing strong intermolecular hydrogen bonds. Segmented poly(ester‐urethane)s were synthesized from dihydroxy‐terminated oligo(propylene succinate)s chain‐extended with 4,4′‐diisophenylmethane diisocyanate. The newly synthesized materials were exhaustively characterized by ¹H NMR spectroscopy, size exclusion chromatography, differential scanning calorimetry, dynamic mechanical analysis, and with respect to their main static mechanical properties, an Instron apparatus was used. The average repeat number of the hard segments, evaluated by NMR, ranged from 4 to 9, whereas that of the flexible segments was about 14. The degree of crystallinity, glass‐transition temperature, melting point, tensile strength, elongation, and Young's modulus were influenced by the ratio between hard and soft segments of the segmented copolymer in a predictable way. The results demonstrated that poly(ester‐urethane)s from 1,3‐propanediol and succinic acid are promising thermoplastics. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 630–639, 2001     

Synthesis,characterization, and crystallization of thermoplastic aromatic semi‐crystalline poly(ester‐imide)s based on bis(trimellitic acid anhydride) phenyl ester

A high molecular weight aromatic homopoly(ester‐imide) (homoPEI) was synthesized from homopoly(ester‐amic acids) (homoPEAA), which was obtained from the reaction of bis(trimellitic acid anhydride) phenyl ester (BTAH) with 4‐4'‐oxydianiline ether (ODA). This homoPEI was melt‐processable semi‐crystalline polymer and displayed dual endothermic transitions which were attributed to the different levels of crystal perfection and size in the crystal structures. Four high molecular weight aromatic copoly(ester‐imide)s (coPEIs) were synthesized via copoly(ester‐amic acids)s (coPEAA) from the reaction of 4, 4'‐oxydiphthalic anhydride (ODPA) and BTAH with ODA. The molar percentage of BTAH varied from 10 to 40%. When the molar percentages of BTAH were 30 and 40%, the resulting two coPEIs were crystallinable and their melting temperatures were 361°C and 356/371°C, respectively. Differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) results indicated that the crystal structures included short segments of BTAH/ODA and ODPA/ODA. The initial crystallization of the two coPEIs took place during imidization process. Thermogravimetric (TA) and mechanical analysis confirmed that both homoPEI and coPEIs showed almost no weight loss until 400°C in N₂ and good mechanical properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Kurt Gottlob – ein Leben für den Kautschuk

The chemist Kurt Gottlob (1881–1925) was one of the best‐known rubber technologists of the early 20th century. Kurt Gottlob's contributions were covering nearly all areas of rubber chemistry. Kurt Gottlob was one of the most important and creative members of the team around Fritz Hofmann (1866–1956) at Farbenfabriken, vorm. Friedr. Bayer, which developed methyl rubber, the world's first synthetic rubber. Together with Fritz Hofmann he discovered the organic accelerators, which revolutionized the vulcanization process of rubber. With his polymerization of isoprene in the presence of aqueous colloidal solutions of albumin he applied the principle of emulsion polymerization for the first time.     

Synthesis and Reactions of 1‐Amino‐5‐morpholin‐4‐yl‐6,7,8,9‐tetrahydrothieno[2,3‐c]isoquinoline

The pyrazolone derivative 4 was synthesized by reaction of carbohydrazide 2 with ethyl benzoylacetate in ethanol and p‐toluene sulphonic acid followed by cyclization upon heating in acetic acid. Chloroacylation of amino ester and amino benzoyl compounds 1 , 19 gave the chloro acetylamino derivatives 5 and 20 respectively which both of them react with different amines to afford compounds 6 , 23a‐d . Hydrolysis and decarboxlation of compound 1 yielded the aminothienotetrahydroisoquinoline 8 which was used as versatile material for synthesizing other heterocyclic compounds 9‐18 . Compound 20 react with hexamethylenetetramine and malononitrile yielded thediazepino and pyrrolo derivatives 21 , 22 respectively.     

Synthesis and thermal stability of S‐trimethylsilyl esters of tetracoordinated phosphorus amidothioacids

S‐(Diethylamino)dimethylsilyl bis(diethylamido)dithiophosphate 3 was obtained by the reaction of tetraphosphorus decasulfide 1 with bis(diethylamino)dimethylsilane 2a . The reactions of Lawesson's reagent 5 with 2a and the alkyl homologues of Davy's reagent 8a,b with trimethyl(diethylamino)silane 6 were studied. On the basis of these reactions, methods of synthesizing S‐(diethylamino)dimethylsilyl or S‐(diethylamino)diphenylsilyl 4‐methoxyphenyl (diethylamido)dithiophosphonates 7a and 7b and S‐trimethylsilyl S‐alkyl(diethylamido)trithiophosphates 9a,b are described. The optimal reaction conditions and thermal stability of S‐trimethylsilyl S‐ethyl(diethylamido)trithiophosphate 9a were defined by differential thermal analyses. Compound 9a have been decomposed to form 2,4‐bis(diethylamido)‐1,3,2,4‐dithiadiphosphetane‐2,4‐disulfide 10 which structure was established by X‐ray single crystal diffraction. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:670–675, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20231     

Facile Synthesis of Well‐Defined Branched Sulfur‐Containing Copolymers: One‐Pot Copolymerization of Carbonyl Sulfide and Epoxide

Topological polymers possess many advantages over linear polymers. However, when it comes to the poly(monothiocarbonate)s, no topological polymers have been reported. Described herein is a facile and efficient approach for synthesizing well‐defined branched poly(monothiocarbonate)s in a “grafting through” manner by copolymerizing carbonyl sulfide (COS) with epichlorohydrin (ECH), where the side‐chain forms in situ. The lengths of the side‐chains are tunable based on reaction temperatures. More importantly, enhancement in thermal properties of the branched copolymer was observed, as the T_g value increased by 22 °C, compared to the linear analogues. When chiral ECH was utilized, semicrystalline branched poly(monothiocarbonate)s were accessible with a T_m value of 112 °C, which is 40 °C higher than that of the corresponding linear poly(monothiocarbonate)s. The strategy presented herein for synthesizing branched polymers provides efficient and concise access to topological polymers.     

Synthesis and liquid crystalline properties of new amide‐modified poly(1,4‐cyclohexanedimethylene terephthalate)

New series of cycloaliphatic poly(ester‐amide)s, poly(1,4‐cyclohexanedimethyleneterephthalate‐co‐1,3‐cyclohexanedimethylene terephthalamide), were synthesized through solution polymerization route. The compositions of ester/amide units in the copolymers were varied from 0 to 100% by varying the amount of 1,4‐cyclohexanedimethanol and 1,3‐cyclohexanebis(methylamine) in the feed. The structures of the polymers were confirmed by NMR and FTIR, and the molecular weights were determined by inherent viscosity. The composition analysis by NMR reveals that the reactivity of the diamine toward the acid chlorides is lowered than that of diol, which results in the formation of more ester content in the poly (ester‐amides). The thermal analysis indicate that the new poly(ester‐amide)s having less than 10 mol % of amide linkages are thermotropic liquid crystalline from 200 to 250 °C and a thread like nematic phases are observed under the polarizing microscope. WXRD studies suggest that the liquid crystalline domains promote the nucleation process in the polyester chains and increases the percent crystallinity of the poly(ester‐amide)s. The glass transition temperature of the copolymers initially increases with increase in amide units because of the presence of nematic phases and subsequently follows the Flory–Fox behavior. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 42–52, 2006     

Synthesis of [2‐aryl‐6‐oxo‐6H‐chromeno[6,7‐d]oxazol‐8‐yl]‐acetic acid ethyl esters

A number of coumarino[6,7‐d]oxazoles (nitrogen analogs of psoralens) have been synthesized from (7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 1 . The synthetic route began with the nitration of 1 with nitric acid in acetic acid to give (6‐nitro‐7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 2 ; (3,6‐dinitro‐7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 3 and (3,6,8‐trinitro‐7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 4 . The reduction of 2 was accomplished with tin(II) chloride, tin, and concentrated hydrochloric acid in ethanol giving (6‐amino‐7‐hydroxy‐2‐oxo‐2H‐chromen‐4‐yl) acetic acid ethyl ester 5 . After the condensation of aminocoumarin 5 with aromatic aldehyde in glacial acetic acid medium, followed the dehydrocyclization to coumarino[6,7‐d]oxazoles 7a‐k . The intermediate Schiff's bases 6a‐k have been obtained from 5 with aromatic aldehyde in ethanol. Antibacterial and antifungal activities of the compounds have been evaluated.     

Polymer Structure‐Guided Self‐Assisted Preparation of Poly(ester‐thioether)‐Based Hollow Porous Microspheres and Hierarchically Interconnected Microcages for Drug Release

Porous polymer microspheres (PPMs) have been widely applied in various biomedical fields. Herein, the self‐assisted preparation of poly(ester‐thioether)‐based porous microspheres and hierarchical microcages, whose pore sizes can be controlled by varying the polymer structures, is reported. Poly(ester‐thioether)s with alkyl side chains (carbon atom numbers were 2, 4, and 8) can generate hollow porous microspheres; the longer alkyl chain length, the larger pore size of microspheres. The allyl‐modified poly(ester‐thioether) (PHBDT‐g‐C₃) can form highly open, hierarchically interconnected microcages. A formation mechanism of these PPMs is proposed; the hydrophobic side chains‐mediated stabilization of oil droplets dictate the droplet aggregation and following solvent evaporation, which is the key to the formation of PPMs. The hierarchically interconnected microcages of PHBDT‐g‐C₃ are due to the partially crosslinking of polymers. Pore sizes of PPMs can be further tuned by a simple mixing strategy of poly(ester‐thioether)s with different pore‐forming abilities. The potential application of these PPMs as H₂O₂‐responsive vehicles for delivery of hydrophobic (Nile Red) and hydrophilic (doxorubicin hydrochloride) cargos is also investigated. The microspheres with larger pore sizes show faster in vitro drug release. The poly(ester‐thioether)‐based polymer microspheres can open a new avenue for the design of PPMs and provide a H₂O₂‐responsive drug delivery platform.     

Synthesis and Thermal Properties of Biodegradable Poly(ester‐urethane)s Based on Chemo‐Synthetic Poly[(R,S)‐3‐hydroxybutyrate]

A series of telechelic oligo[(R,S)‐3‐hydroxybutyrate]‐diols (PHB‐diols) was synthesized from ethyl (R,S)‐3‐hydroxybutyrate (ethyl (HB)) and four different aliphatic diols, namely, 1,4‐butanediol, 1,6‐hexanediol, 1,8‐octanediol and 1,10‐decanediol by transesterification and condensation in bulk. The structures of the synthesized oligomers were confirmed by ¹H NMR spectroscopy and MALDI‐TOF mass spectroscopy. The use of 1,4‐butanediol results in an oligoester with hydroxyl functionality of approximately 2. In the case of the higher aliphatic diols, the number average functionalities were found to be lower than 2. These differences were ascribed to side reactions which occur during polymerization, yielding unreactive end groups. Other novel families of biodegradable poly(ester‐urethane)s were synthesized either from PHB‐diol alone, or PHB‐diol mixed with poly(ε‐caprolactone)‐diol (PCL‐diol), poly(butylene adipate)‐diol (PBA‐diol) or poly(diethylene glycol adipate)‐diol (PDEGA‐diol). In each case, 1,6‐hexamethylene diisocyanate was used as a nontoxic connecting agent. The homopolymers prepared from PCL‐diol, PBA‐diol and PDEGA‐diol were also synthesized for the sake of comparison. All the prepared copolymers possess high molecular weight with glass transition temperature (T_g) values varying from –54 to –23°C. Some of the prepared copoly(ester‐urethane)s are partially crystalline with melting temperatures (T_m's) varying from 37 to 56°C.