Photosensitive polybenzoxazole based on a poly(o‐hydroxy amide), a dissolution inhibitor,and a photoacid generator

A positive‐type photosensitive polybenzoxazole (PSPBO), based on a poly(o‐hydroxy amide) (PHA), the dissolution inhibitor (DI) 9,9‐bis(4‐tert‐butoxycarbonyloxyphenyl)fluorene (t‐Boc BHF), and the photoacid generator (5‐propylsulfonyloxyimino‐5H‐thiophene‐2‐ylidene)‐(2‐methylphenyl)acetonitrile (PTMA), was developed. Several new tert‐butoxycarbonylated compounds as DIs for PSPBOs were prepared from phenolic compounds having a cardolike structure with di‐tert‐butyl dicarbonate in the presence of 4‐dimethylaminopyridine. Among them, t‐Boc BHF and 5,5′,6,6′‐tetra(tert‐butoxycarbonyl)‐3,3,3′,3′‐tetramethyl‐1,1′‐spirobiindane acted as excellent DIs, giving a large dissolution contrast between the exposed and unexposed areas in a 2.38 wt % tetramethylammonium hydroxide solution (TMAHaq)/5 wt % iso‐propanol (i‐PrOH). The dissolution behavior of this PSPBO system was studied in relation to the PTMA and t‐Boc BHF loadings and postexposure baking temperature. A PSPBO consisting of PHA (77 wt %), t‐Boc BHF (20 wt %), and PTMA (3 wt %) exhibited a sensitivity of 34 mJ/cm² and a contrast of 5.8 when exposed to 365‐nm light (i‐line) and developed with an aqueous alkaline developer, 2.38 wt % TMAHaq/5 wt % i‐PrOH. A clear, positive image with 6‐μm features and a 10‐μm‐thick pattern with high sensitivity and contrast was produced by contact printing and converted into polybenzoxazole patterns upon heating at 350 °C for 1 h. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 661–668, 2007     

Biosynthesis of Streptolidine Involved Two Unexpected Intermediates Produced by a Dihydroxylase and a Cyclase through Unusual Mechanisms

Streptothricin‐F (STT‐F), one of the early‐discovered antibiotics, consists of three components, a β‐lysine homopolymer, an aminosugar D ‐gulosamine, and an unusual bicyclic streptolidine. The biosynthesis of streptolidine is a long‐lasting but unresolved puzzle. Herein, a combination of genetic/biochemical/structural approaches was used to unravel this problem. The STT gene cluster was first sequenced from a Streptomyces variant BCRC 12163, wherein two gene products OrfP and OrfR were characterized in vitro to be a dihydroxylase and a cyclase, respectively. Thirteen high‐resolution crystal structures for both enzymes in different reaction intermediate states were snapshotted to help elucidate their catalytic mechanisms. OrfP catalyzes an Fe^II‐dependent double hydroxylation reaction converting L ‐Arg into (3R,4R)‐(OH)₂‐L ‐Arg via (3S)‐OH‐L ‐Arg, while OrfR catalyzes an unusual PLP‐dependent elimination/addition reaction cyclizing (3R,4R)‐(OH)₂‐L ‐Arg to the six‐membered (4R)‐OH‐capreomycidine. The biosynthetic mystery finally comes to light as the latter product was incorporation into STT‐F by a feeding experiment.     

Toward the Total Synthesis of Onchidin,a Cytotoxic Cyclic Depsipeptide from a Mollusc

The total synthesis of onchidin ( 1 ), a cytotoxic, C₂‐symmetric cyclic decadepsipeptide from a marine mollusc, according to the published structure, is described. A novel β‐amino acid, (2S,3S)‐3‐amino‐2‐methyl‐7‐octynoic acid (AMO), was efficiently prepared in high yield with high diastereo‐ and enantioselectivity based on a catalytic asymmetric three‐component Mannich‐type reaction with a chiral zirconium catalyst. The formation of sterically unfavorable N‐methyl amide and hindered ester bonds were successfully demonstrated, and final macrocyclization was achieved at a secondary‐amide site. Completion of the synthesis of 1 suggested that a revision of the structure of the natural product is required. Two diastereomers were also synthesized as candidates for the actual structure of onchidin. Furthermore, efficient solid‐phase methods were employed for the combinatorial synthesis of other derivatives to clarify the real structure of onchidin. The solid‐phase assembly of a pentadepsipeptide containing all the building blocks was established followed by dimeric cyclization in solution.     

Morphological change of a diblock copolymer film induced by selective doping of a photoactive chromophore

Tetrakis‐5,10,15,20‐(4‐carboxyphenyl)porphyrine (TCPP) was position‐selectively introduced into a diblock copolymer film of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) with a sea–island microphase structure. By immersing the PS‐b‐P4VP film into a solution of TCPP/methanol, TCPP was introduced into the island parts comprising P4VP phase. The morphology of the island parts depended on the immersion time and TCPP concentration. A schematic model for the morphological change caused by the phase‐selective introduction of TCPP was proposed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 368–375, 2007     

Synthetic Studies on Kinamycin Antibiotics: Synthesis of a Trioxygenated Benz[f]indenone and its Diels–Alder Reaction to a Kinamycin Skeleton

A benzo[b]fluorene skeleton such as 10 , a basic four‐ring system in the revised diazo structures 3 of kinamycin antibiotics, was synthesized by Diels‐Alder reaction between dienophile 4,7,8‐trioxygenated 1H‐benz[f]inden‐1‐one 11 and Danishefsky‐type diene 7 . The indenone 11 was prepared by deoxygenation of 2,3‐dihydro‐1H‐benz[f]inden‐1‐one 12 with the inexpensive 1‐hydroxy‐1,2‐benziodoxol‐3(1H)‐one 1‐oxide (IBX) after modification of the known protocol. Indenone 12 in turn was obtained from naphthalene‐1,5‐diol ( 14 ) via an intramolecular Friedel‐Crafts cyclization of naphthalene‐2‐propanoic acid 13 as a key step.     

Porphyrin Analogues of a Trityl Cation and Anion

Porphyrin‐stabilized meso‐ or β‐carbocations were generated upon treatment of the corresponding bis(4‐tert‐butylphenyl)porphyrinylcarbinols with trifluoroacetic acid (TFA). Bis(4‐tert‐butylphenyl)porphyrinylcarbinols were treated with TFA to generate the corresponding carbocations stabilized by a meso‐ or β‐porphyrinyl group. The meso‐porphyrinylmethyl carbocation displayed more effective charge delocalization with decreasing aromaticity compared with the β‐porphyrinylmethyl carbocation. A propeller‐like porphyrin trimer, tris(β‐porphyrinyl)carbinol, was also synthesized and converted to the corresponding cation that displayed a more intensified absorption reaching over the NIR region. meso‐Porphyrinylmethyl carbanion was generated as a stable species upon deprotonation of bis(4‐tert‐butylphenyl)(meso‐porphyrinyl)methane with potassium bis(trimethylsilyl)amide (KHMDS) and [18]crown‐6, whereas β‐porphyrinylmethyl anions were highly unstable.     

Photocontrol of the Catalytic Activity of a β‐Cyclodextrin Bearing Azobenzene and Histidine Moieties as a Pendant Group

An azobenzene group was linked to β‐cyclodextrin via a histidine spacer ( 1 ) to produce a photoresponsive catalyst. The ester hydrolysis of p‐nitrophenyl acetate, Boc‐L ‐alanine‐p‐nitrophenyl ester and Boc‐D ‐alanine‐p‐nitrophenyl ester was examined in the presence of trans‐ 1 or cis‐ 1 . In the case of cis‐ 1 , the cyclodextrin cavity was used as the substrate binding site during imidazole‐catalyzed ester hydrolysis. This was not possible in the case of trans‐ 1 due to the inclusion of the trans‐azobenzene moiety in the cyclodextrin cavity. Consequently, the catalytic mechanism switches in an on‐off fashion on UV irradiation, associated with the conversion of the azobenzene moiety of 1 from trans to cis.     

A Concise Route to Racemic Anatoxin a from Cycloocta‐1,5‐diene

The synthesis of racemic anatoxin a ( 1a ) from cycloocta‐1,5‐diene via its 1 : 1 cycloadduct with N‐chlorosulfonyl isocyanate is described. The N‐unsubstituted β‐lactam 2b was converted to a β‐amino ester 3 which was then submitted to a Pd‐catalyzed cyclization to afford the conjugated ester 4a . The N‐tosyl derivative 4b was then elaborated into N‐tosylanatoxin a ( 1b ) via a Weinreb amide.     

Paranolin: a New Xanthene‐Based Metabolite from Paraphaeosphaeria nolinae

A new xanthene‐based, polycyclic metabolite, paranolin (= (2R,3aS,12aR)‐3,3a‐dihydro‐3a‐hydroxy‐8‐(hydroxymethyl)‐2‐(1‐hydroxy‐1‐methylethyl)‐9‐methoxy‐10‐methylfuro[3,2‐d]xanthen‐6(2H)‐one; 1 ) was isolated from a culture of Paraphaeosphaeria nolinae (IFB‐E011), an endophytic fungus residing in the normal stem of the artemisinin‐producing plant Artemisia annua (Asteraceae). The structure of 1 was elucidated by extensive spectroscopic analyses. Although not substantially active against the human colon (SW1116) and human cervical carcinoma (Hela) cell lines, this metabolite seems to be the first example of a xanthene‐derived secondary metabolite. Its possible biosynthetic origin (Scheme) and its significance as a phyllogenetic marker are discussed in brief.     

Direct patterning of poly(amic acid) and low‐temperature imidization using a crosslinker,a photoacid generator,and a thermobase generator

A positive‐type photosensitive polyimide (PSPI) based on poly(amic acid) (PAA), a crosslinker 1,1,1‐tris{4‐[2‐(vinyloxy)ethoxy]phenyl}ethane (TVPE), a photoacid generator (PAG) (5‐propylsulfonyloxyimino‐5H‐thiophen‐2‐ylidene)‐2‐(methylphenyl)acetonitrile (PTMA), and a thermobase generator (TBG) t‐butyl 2,6‐dimethylpiperidine‐1‐carboxylate (BDPC) has been developed as a promising material in microelectronics. The PAA was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianiline (ODA) in dimethyl sulfoxide (DMSO). The PSPI, consisting of PAA (69 wt %), TPVE (21 wt %), PTMA (3 wt %), and BDPC (7 wt %), showed high sensitivity of 21 mJ/cm² and a high contrast of 6.8 when it was exposed to a 436‐nm line (g‐line), postbaked at 90 °C for 5 min, and developed with 1.69 wt % TMAHaq. A clear positive image of 8 μm line and space pattern was printed on film, which was exposed to 50 mJ/cm² of g‐line by a contact printing mode and fully converted to the corresponding polyimide (PI) pattern on heating at 200 °C, confirmed by FTIR spectroscopy. Thus, this system will be a good candidate for next generation PSPIs. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3362–3369, 2009     

Atom transfer radical polymerization of cyclohexyl methacrylate at a low temperature

The atom transfer radical polymerization of cyclohexyl methacrylate (CHMA) is reported. Controlled polymerizations were performed with the CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalytic system with ethyl 2‐bromoisobutyrate as the initiator in bulk and different solvents (25 vol %) at 40 °C. The polymerization of CHMA in bulk resulted in a controlled polymerization, although the concentration of active species was relatively elevated. The addition of a solvent was necessary to reduce the polymerization rate, which was dependent on the dipole moment. Well‐controlled polymers were obtained in toluene, diphenyl ether, and benzonitrile solutions. Poly(cyclohexyl methacrylate) as a macroinitiator was used to synthesize the poly(cyclohexyl methacrylate)‐b‐poly(tert‐butyl methacrylate) block copolymer, which allowed a demonstration of its living character. In addition, two difunctional initiators, 1,4‐bis(bromoisobutyryloxy) benzene and 1,2‐bis(bromoisobutyryloxy) ethane, were used to initiate the atom transfer radical polymerization of CHMA. The experimental molecular weights of the obtained polymers were very close to the theoretical ones. These, along with the relative narrow molecular weight distributions, indicated that the polymerization was living and controlled. For confirmation, two different poly(tert‐butyl methacrylate)‐b‐poly(cyclohexyl methacrylate)‐b‐poly(tert‐butyl methacrylate) triblock copolymers were also synthesized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 71–77, 2005     

Azadirachtol,a tetranortriterpenoid from neem kernels

The title compound, di­methyl (?)‐(2aR,3R,4R,4aS,5R,7aS,8R,10S,10aR)‐3,8,10‐tri­hydroxy‐4‐[(2R,6R)‐2‐hydroxy‐11‐methyl‐5,7,10‐trioxatetra­cyclo­[6.3.1.0^2,60^9,11]­dodec‐3‐en‐9‐yl]‐4‐methyl­per­hydro­isobenzo­furano­[5,4,3a‐cd]­isobenzofuran‐5,10a‐di­acetate, C₂₈H₃₆O₁₃, which exhibits higher antifeedant activity than azadirachtin‐A, a known potent antifeedant, was isolated from neem kernels. The asymmetric unit of the structure contains two independent mol­ecules, which differ in the conformations of their functional groups and also in the conformations of some of the rings. The relative orientation between the decalin and furan­yl moieties is similar to that observed in the majority of azadirachtin structures, but is different from that in azadirachtin‐A. The two symmetry‐independent mol­ecules are linked into dimeric units by intermolecular O—H?O hydrogen bonds.     

Characteristic properties of film prepared from poly(L‐lactide)‐grafted dextran of a relatively high sugar unit content as a degradable biomaterial

To develop novel biomedical soft materials with degradability, amphiphilic poly(L ‐lactide)‐grafted dextrans (Dex‐g‐PLLAs) of relatively high sugar unit contents were synthesized with the trimethylsilyl protection method. The characteristic properties of solution‐cast films prepared from the obtained Dex‐g‐PLLAs were investigated. The water absorption and degradation rate of the Dex‐g‐PLLA films increased with increasing sugar unit content. The morphology of the bulk phase and top surface of the Dex‐g‐PLLA films was evaluated with transmission electron microscopy and atomic force microscopy, respectively. The bulk phase of the Dex‐g‐PLLA films with a sugar unit content of 16–25 wt % was found by transmission electron microscopy to form a lamellar type of phase‐separated structure composed of approximately 80–100‐nm‐wide nanodomains because of their amphiphilic and branched structures. The hydrophobic top surface for a Dex‐g‐PLLA film with a sugar unit content of 25 wt % covered with PLLA segments was confirmed by atomic force microscopy phase images to be easily converted to a wettable top surface covered with hydrophilic dextran aggregates showing an 8–10‐nm‐wide honeycomb pattern by means of annealing in water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6402–6409, 2006     

Quantitative analysis of 3‐OHB[a]P and (+)‐anti‐BPDE as biomarkers of B[a]P exposure in rats

The aim of this study was to develop an analytical method for the determination the levels of metabolites of benzo[a]pyrene (B[a]P), 3‐hydroxybenzo(a)pyrene (3‐OHB[a]P) and (+)‐anti‐benzo(a)pyrene diol‐epoxide [(+)‐anti‐BPDE, combined with DNA to form adducts], in rat blood and tissues exposed to B[a]P exposure by high‐performance liquid chromatography with fluorescence detection (HPLC/FD), and to investigate the usefulness of 3‐OHB[a]P and (+)‐anti‐BPDE as markers of intragastrical exposure to B[a]P in rats. The levels of 3‐OH‐B[a]P and B[a]P‐tetrol I‐1 released after acid hydrolysis of (+)‐anti‐BPDE in the samples were measured by HPLC/FD. The calibration curves were linear (r² > 0.9904), and the lower limit of quantification ranged from 0.34 to 0.45 ng/mL for 3‐OHB[a]P and from 0.43 to 0.58 ng/mL for (+)‐anti‐BPDE. The intra‐ and inter‐day stability assay data suggested that the method is accurate and precise. The recoveries of 3‐OHB[a]P and (+)‐anti‐BPDE were in the ranges of 73.6 ± 5.0 to 116.5 ± 6.3% and 73.3 ± 8.5 to 141.2 ± 13.8%, respectively. A positive correlation was found between the concentration of intragastrical B[a]P and the concentrations of 3‐OH‐B[a]P and (+)‐anti‐BPDE in the blood and in most of the tissues studied, except for the brain and kidney, which showed no correlation between B[a]P and 3‐OHB[a]P and between B[a]P and (+)‐anti‐BPDE, respectively. A sensitive, reliable and rapid HPLC/FD was developed and validated for analysis of 3‐OHB[a]P and (+)‐anti‐BPDE in rat blood and tissues. There was a positive correlation between the concentration of 3‐OHB[a]P or (+)‐anti‐BPDE in the blood and the concentration of 3‐OHB[a]P or (+)‐anti‐BPDE in the most other tissues examined. The concentration of 3‐OHB[a]P or (+)‐anti‐BPDE in the blood could be used as an indicator of the concentration of 3‐OHB[a]P or (+)‐anti‐BPDE in the other tissues in response to B[a]P exposure. These results demonstrate that 3‐OHB[a]P and (+)‐anti‐BPDE are potential biomarkers of B[a]P exposure, which would also be useful to assess the carcinogenic risks from B[a]P exposure. Copyright © 2015 John Wiley & Sons, Ltd.     

Oligonucleosides with a Nucleobase‐Including Backbone. Part 12

In contradistinction to the corresponding Grignard reagent, bis[(trimethylsilyl)ethynyl]zinc reacted with the 5′‐oxoadenosine 3 diastereoselectively to the β‐D ‐allo‐hept‐6‐ynofuranosyladenine 5 . Lithiation/iodination of the monomeric propargyl alcohol 5 and of the dimeric propargyl alcohol 22 provided the 8‐iodoadenosines 7 and 18 , respectively, considerably shortening the synthesis of the dimeric O‐silylated 8‐iodoadenosine 25 . The mixed uridine‐ and adenosine‐derived tetramers 21 and 32 were synthesised. The tetramer 21 was prepared by a linear sequence. Sonogashira coupling of 9 and 13 yielded the trimer 16 that was C‐desilylated to 17 . A second Sonogashira coupling of 17 and 19 yielded the tetramer 21 . Tetramer 32 was prepared in higher yields by a convergent route, coupling the acetylene 29 and the iodide 30 . The uridine‐derived iodides proved more reactive than the adenosine‐derived analogues, and the N⁶‐unprotected adenosine‐derived alkynes were more reactive than their N⁶‐benzoylated analogues.     

Alkyl substituted phenoxyl decay in a hydrogen transfer equilibrium

The kinetics of radical decay in the equilibrium: 2,4,6‐tri‐tert‐butylphenoxyl radical 1 + 2,6‐di‐tert‐butyl‐4‐methylphenol 2 = 2,4,6‐tri‐tert‐butylphenol 3 + 2,6‐di‐tert‐butyl‐4‐methylphenoxyl radical 4 was studied at 298 and 273 K by means of EPR spectroscopy. At 298 K second order prevails, whereas at 273 K the best fit was order 3/2. The extinction of 4 takes place in two steps: dimerization followed by disproportionation of the dimer, but the stable radical 1 enters in crossed dimerization with 4 to yield nonradical products. The mechanism ensures a constant [ 4 ]/[ 1 ] ratio along the decay. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 1–4, 2005     

Preparation of a monolithic column with a mixed‐mode stationary phase of reversed‐phase/hydrophilic interaction for capillary liquid chromatography

A monolithic capillary column with a mixed‐mode stationary phase of reversed‐phase/hydrophilic interaction chromatography was prepared for capillary liquid chromatography. The monolith was created by an in‐situ copolymerization of a homemade monomer N,N‐dimethyl‐N‐acryloxyundecyl‐N‐(3‐sulfopropyl) ammonium betaine and a crosslinker pentaerythritol triacrylate in a binary porogen agent consisting of methanol and isopropanol. The functional monomer was designed to have a highly polar zwitterionic sulfobetaine terminal group and a hydrophobic long alkyl chain moiety. The composition of the polymerization solution was systematically optimized to permit the best column performance. The columns were evaluated by using acidic, basic, polar neutral analytes, as well as a set of alkylbenzenes and Triton X100. Very good separations were obtained on the column with the mixed‐mode stationary phase. It was demonstrated that the mixed‐mode stationary phase displayed typic dual retention mechanisms of reversed‐phase/hydrophilic interaction liquid chromatography depending on the content of acetonitrile in the mobile phase. The method for column preparation is reproducible.     

Identification of the Structural Determinants for Anticancer Activity of a Ruthenium Arene Peptide Conjugate

Organometallic Ru(arene)–peptide bioconjugates with potent in vitro anticancer activity are rare. We have prepared a conjugate of a Ru(arene) complex with the neuropeptide [Leu⁵]‐enkephalin. [Chlorido(η⁶‐p‐cymene)(5‐oxo‐κO‐2‐{(4‐[(N‐tyrosinyl‐glycinyl‐glycinyl‐phenylalanyl‐leucinyl‐NH₂)propanamido]‐1H‐1,2,3‐triazol‐1‐yl)methyl}‐4H‐pyronato‐κO)ruthenium(II)] ( 8 ) shows antiproliferative activity in human ovarian carcinoma cells with an IC₅₀ value as low as 13 μM , whereas the peptide or the Ru moiety alone are hardly cytotoxic. The conjugation strategy for linking the Ru(cym) (cym=η⁶‐p‐cymene) moiety to the peptide involved N‐terminal modification of an alkyne‐[Leu⁵]‐enkephalin with a 2‐(azidomethyl)‐5‐hydroxy‐4H‐pyran‐4‐one linker, using Cu^I‐catalyzed alkyne–azide cycloaddition (CuAAC), and subsequent metallation with the Ru(cym) moiety. The ruthenium‐bioconjugate was characterized by high resolution top‐down electrospray ionization mass spectrometry (ESI‐MS) with regard to peptide sequence, linker modification and metallation site. Notably, complete sequence coverage was obtained and the Ru(cym) moiety was confirmed to be coordinated to the pyronato linker. The ruthenium‐bioconjugate was analyzed with respect to cytotoxicity‐determining constituents, and through the bioconjugate models [{2‐(azidomethyl)‐5‐oxo‐κO‐4H‐pyronato‐κO}chloride (η⁶‐p‐cymene)ruthenium(II)] ( 5 ) and [chlorido(η⁶‐p‐cymene){5‐oxo‐κO‐2‐([(4‐(phenoxymethyl)‐1H‐1,2,3‐triazol‐1‐yl]methyl)‐4H‐pyronato‐κO}ruthenium(II)] ( 6 ) the Ru(cym) fragment with a triazole‐carrying pyronato ligand was identified as the minimal unit required to achieve in vitro anticancer activity.     

N‐N migration of a carbamoyl group in a pyrazole derivative revealed by NMR

During a synthesis of 5‐amino‐4‐(6‐methoxy‐2‐methylpyridin‐3‐yl)‐3‐methyl‐1H‐pyrazole‐1‐carboxamide (see Scheme 1), a side‐reaction produced 3‐amino‐4‐(6‐methoxy‐2‐methylpyridin‐3‐yl)‐5‐methyl‐1H‐pyrazole‐1‐carboxamide as a by‐product that forms an equilibrium with the target‐compound. The structure of the by‐product was elucidated by the interpretation of 1D and 2D (HMQC, HMBC) NMR data where ¹H‐¹⁵ N HMBC correlations revealed the position of carbamoyl group attachment on the pyrazole. Comparison of structures of the target‐compound and the by‐product showed that the latter resulted from N‐N migration of the carbamoyl group in the target‐compound. Copyright © 2013 John Wiley & Sons, Ltd.     

Anionic ring‐opening polymerization of a five‐membered cyclic carbonate having a glucopyranoside structure

Anionic ring‐opening polymerizations of methyl 4,6‐O‐benzylidene‐2,3‐O‐carbonyl‐α‐D ‐glucopyranoside (MBCG) were investigated using various anionic polymerization initiators. Polymerizations of the cyclic carbonate readily proceeded by using highly active initiators such as n‐butyllithium, lithium tert‐butoxide, sodium tert‐butoxide, potassium tert‐butoxide, and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene, whereas it did not proceed by using N,N‐dimethyl‐4‐aminopyridine and pyridine as initiators. In a polymerization of MBCG (1.0 M), 99% of MBCG was converted within 30 s to give the corresponding polymer with number‐averaged molecular weight (M_n) of 16,000. However, the M_n of the polymer decreased to 7500 when the polymerization time was prolonged to 24 h. It is because a backbiting reaction might occur under the polymerization conditions. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013