New class of cationic ring‐opening polymerizations of 2,2‐diphenyl‐1,3‐oxathiolanes accompanying quantitative elimination of benzophenone

Cationic polymerizations of three 2‐substituted 1,3‐oxathiolanes, 2,2‐diphenyl‐1,3‐oxathiolane ( 1a ), 5‐methyl‐2,2‐diphenyl‐1,3‐oxathiolane ( 1b ), and 4‐methyl‐2,2‐diphenyl‐1,3‐oxathiolane ( 1c ), were carried out with boron trifluoride etherate (BF₃ · OEt₂) in dichloromethane at 30 °C to obtain poly(alkylene sulfide)s accompanying the elimination of benzophenone. In the cationic polymerization of 1b and 1c , the consumption of the monomers and formation of benzophenone proceeded simultaneously. The obtained poly(propylene sulfide)s from 1b and 1c contain 41% head–head units, which is in good agreement with that of the polymer from methylthiirane with BF₃ · OEt₂. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2943–2949, 2004     

PPh3‐catalyzed knoevenagel condensation: A facile synthesis of 5‐(1H‐indol‐3‐yl)Meth‐ ylene)‐2, 2‐Dimethyl‐1, 3‐Dioxane‐4, 6‐dione,and their N‐alkyl derivatives by using peg‐600 as the reaction medium

Triphenylphosphine (TPP) has been utilized as a novel and efficient catalyst for the Knoevenagel condensation of indole‐3‐carboxaldehydes 1(a–e) , 1‐methyl‐1H‐indole‐3‐carboxaldehydes 4(a–e) , and 1‐ethyl‐1H‐indole‐3‐carboxaldehydes 6(a–e) with the active methylene compound, that is, meldrum's acid ( 2 ), to afford substituted derivatives 5‐((1H‐indol‐3‐yl) methylene)‐2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione 3(a–e) , 2,2‐dimethyl‐5‐((1‐methyl‐1H‐indol‐3‐yl)methylene)‐1,3‐dioxane‐4,6‐dione 5(a–e) , and 2,2‐dimethyl‐5‐((1‐ethyl‐1H‐indol‐3‐yl)methylene)‐1,3‐dioxane‐4,6‐dione 7(a–e) , respectively, in ethanol medium at RT just within 1 h in excellent yields. The products 3(a–e) were reacted independently with alkylating agents, that is, DMS and DES in the presence of PEG‐600 as an efficient and green solvent, to afford the corresponding N‐substituted methyl and ethyl derivatives 5(a–e) and 7(a–e) , respectively. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:41–48, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20750     

Synthesis of phosphate‐pendant polymers and their application to thermally latent polymeric initiators

A novel phosphate monomer, O‐p‐(methacryloyloxymethyl)benzyl O,O‐diethyl phosphate (MDP) was synthesized by the reaction of diethyl phosphorochloridate with 1,4‐benzenedimethanol, followed by the reaction with methacryloyl chloride in the presence of triethylamine. The radical polymerization of MDP and copolymerization with methyl methacrylate were carried out in the presence of 2,2′‐azobisisobutyronitrile (3 mol %) in dimethylacetamide at 60 °C for 20 h to afford phosphate‐pendant polymers. The polymerization of glycidyl phenyl ether (GPE) was carried out with the phosphate‐pendant polymer as an initiator in the presence of ZnCl₂. The polymerization did not proceed below 90 °C but rapidly proceeded above 90 °C to afford polyGPE. The phosphate‐pendant polymer served as a good thermally latent polymeric initiator. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3365–3370, 2001     

Hydrogen‐transfer polymerization of vinyl monomers derived from 4‐methylbenzoyl isocyanate and acrylamide derivatives

The anionic polymerization of N‐acryloyl‐N′‐(4‐methylbenzoyl)urea (1) was carried out at 80°C for 24 h in DMF, DMSO, acetonitrile, or toluene by t‐BuOK or DBU (3 mol %) as an initiator to obtain polymer 3 in a good yield. The structure of 3 was dependent upon the initiator used, in which t‐BuOK selectively conducted the hydrogen‐transfer polymerization, while DBU partially induced the vinyl polymerization (16–20%). Likewise, N‐acryloyl‐N‐methyl‐N′‐(4‐methylbenzoyl)urea (2, i.e., an N‐methylated derivative of 1) was subjected to the hydrogen‐transfer polymerization. Although the yield of the polymer was lower in comparison with 1, the structure of the obtained polymer 4 was similarly governed by the initiator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 465–472, 1999     

Controlled cationic ring‐opening polymerization of cyclic thiocarbonates with ester groups

This work deals with the cationic ring‐opening polymerization of the cyclic thiocarbonates 5‐benzoyloxymethyl‐5‐methyl‐1,3‐dioxane‐2‐thione ( 1 ), 5,5‐dimethyl‐1,3‐dioxane‐2‐thione ( 2 ), and 4‐benzoyloxymethyl‐1,3‐dioxane‐2‐thione ( 3 ). The polymerization was carried out with 2 mol % trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, boron trifluoride etherate, or triethyloxonium tetrafluoroborate as the initiator to afford the polythiocarbonate with a narrow molecular weight distribution accompanying isomerization of the thiocarbonate group. The molecular weight of the obtained polymer could be controlled by the feed ratio of the monomer to the initiator and increased when the second monomer was added to the polymerization mixture after the quantitative consumption of the monomer in the first stage. The block copolymerization of 2 and 3 was also achieved, and this supported the idea that the cationic ring‐opening polymerization of these monomers proceeded via a living process. The order of the polymerization rate was 3 > 2 > 1 . The cationic ring‐opening polymerization of 1 and 3 involved the neighboring group participation of ester groups according to the polymerization rate and molecular orbital calculations with the ab initio method. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 185–195, 2003     

Synthesis and chemical modification of hyperbranched polyethers with terminal hydroxy groups by the anionic ring‐opening polymerization of 3‐alkyl‐3‐hydroxymethyl oxetanes

The anionic ring‐opening polymerization of oxetanes containing hydroxyl groups was carried out with potassium tert‐butoxide as an initiator in the presence of 18‐crown‐6‐ether in N‐methylpyrrolidinone at 180 °C; it yielded corresponding multifunctional hyperbranched polymers: poly(3‐ethyl‐3‐hydroxymethyloxetane)s, with number‐average molecular weights of 2200–4100 in 83–95% yields, and poly(3‐methyl‐3‐hydroxymethyloxetane)s, with number‐average molecular weights of 4600–5200 in 70–95% yields. The synthesized poly(3‐ethyl‐3‐hydroxymethyloxetane)s and poly(3‐methyl‐3‐hydroxymethyloxetane)s were hyperbranched polyethers containing an oxetane moiety and many hydroxy groups at the ends. The postpolymerization of poly(3‐ethyl‐3‐hydroxymethyloxetane)s was performed in the presence of potassium tert‐butoxide and 18‐crown‐6‐ether in N‐methylpyrrolidinone at 180 °C; it yielded corresponding polymers with higher molecular weights in good yields. The cationic polymerization of poly(3‐ethyl‐3‐hydroxymethyloxetane) derivatives was carried out with boron trifluoride etherate as an initiator and was followed by alkaline hydrolysis; this yielded a new branched polymer, a poly(hyperbranched polyether), with many pendant hydroxy groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3739–3750, 2004     

Effective Methods for the Synthesis of N‐Methyl β‐Amino Acids from All Twenty Common α‐Amino Acids Using 1,3‐Oxazolidin‐5‐ones and 1,3‐Oxazinan‐6‐ones

N‐Methyl β‐amino acids are generally required for application in the synthesis of potentially bioactive modified peptides and other oligomers. Previous work highlighted the reductive cleavage of 1,3‐oxazolidin‐5‐ones to synthesise N‐methyl α‐amino acids. Starting from α‐amino acids, two approaches were used to prepare the corresponding N‐methyl β‐amino acids. First, α‐amino acids were converted to N‐methyl α‐amino acids by the so‐called ‘1,3‐oxazolidin‐5‐one strategy’, and these were then homologated by the Arndt–Eistert procedure to afford N‐protected N‐methyl β‐amino acids derived from the 20 common α‐amino acids. These compounds were prepared in yields of 23–57% (relative to N‐methyl α‐amino acid). In a second approach, twelve N‐protected α‐amino acids could be directly homologated by the Arndt–Eistert procedure, and the resulting β‐amino acids were converted to the 1,3‐oxazinan‐6‐ones in 30–45% yield. Finally, reductive cleavage afforded the desired N‐methyl β‐amino acids in 41–63% yield. One sterically congested β‐amino acid, 3‐methyl‐3‐aminobutanoic acid, did give a high yield (95%) of the 1,3‐oxazinan‐6‐one ( 65 ), and subsequent reductive cleavage gave the corresponding AIBN‐derived N‐methyl β‐amino acid 61 in 71% yield (Scheme 2). Thus, our protocols allow the ready preparation of all N‐methyl β‐amino acids derived from the 20 proteinogenic α‐amino acids.     

Polycondensation of α‐amino acid esters in the presence of yttrium triflate as a Lewis acid

To develop polycondensation methods for poly(α‐amino acid)s, we describe a first examination to use yttrium triflate as a Lewis acid for polycondensation of α‐amino acid esters. In the absence of Lewis acid, no polycondensation of 2‐methoxyphenyl glycinate ( 1b ) at room temperature proceeded. While the polycondensation of 1b was carried out with 5 mol % yttrium triflate, a condensation product of glycine was obtained in 16% yield. Although polycondensation of 4‐nitrophenyl L ‐leucinate ( 1c ) and 4‐nitrophenyl L ‐valinate ( 1d ) were also promoted with 5 mol % yttrium triflate, the condensation products of both α‐amino acid esters were obtained in only a few percent yield. When 1d was polymerized in the presence of 100 mol % yttrium triflate, high molecular weight poly(L ‐valine) was obtained in 91% yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4731–4735, 2006     

Formation of 2‐(Phenylsulfonyl)resorcinols (=2‐(Phenylsulfonyl)benzene‐1,3‐diols) from Symmetrically Substituted Maleic Anhydrides (=Furan‐2,5‐diones)

Treatment of symmetrically substituted maleic anhydrides (=furan‐2,5‐diones) 6 with lithium (phenylsulfonyl)methanide, followed by methylation of the adduct with MeI/K₂CO₃ in acetone, give the corresponding 4,5‐disubstituted 2‐methyl‐2‐(phenylsulfonyl)cyclopent‐4‐ene‐1,3‐diones 8 (Scheme 3). Reaction of the latter with lithium (phenylsulfonyl)methanide in THF (?78°) and then with 4 mol‐equiv. BuLi (?5° to r.t.) leads to 5,6‐disubstituted 4‐methyl‐2‐(phenylsulfonyl)benzene‐1,3‐diols 9 (Scheme 4).     

Polymerization of o‐quinodimethanes. IV. Radical polymerization of 1‐cyano‐o‐quinodimethane in the presence of TEMPO

The radical polymerization behavior of 1‐cyano‐o‐quinodimethane generated by thermal isomerization of 1‐cyanobenzocyclobutene in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxide (TEMPO) and the block copolymerization of the obtained polymer with styrene are described. The radical polymerization of 1‐cyanobenzocyclobutene was carried out in a sealed tube at temperatures ranging from 100 to 150 °C for 24 h in the presence of di‐tert‐butyl peroxide (DTBP) as a radical initiator and two equivalents of TEMPO as a trapping agent of the propagation end radical to obtain hexane‐insoluble polymer above 130 °C. Polymerization at 150 °C with 5 mol % of DTBP in the presence of TEMPO resulted in the polymer having a number‐average molecular weight (M_n ) of 2900 in 63% yield. The structure of the obtained polymer was confirmed as the ring‐opened polymer having a TEMPO unit at the terminal end by ¹H NMR, ¹³C NMR, and IR analyses. Then, block copolymerization of the obtained polymer with styrene was carried out at 140 °C for 72 h to give the corresponding block copolymer in 82% yield, in which the unimodal GPC curve was shifted to a higher molecular weight region. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3434–3439, 2000     

Polar,functionalized diene‐based material. III. Free‐radical polymerization of 2‐[(N,N‐dialkylamino)methyl]‐1,3‐butadienes

The bulk free‐radical polymerization of 2‐[(N,N‐dialkylamino)methyl]‐1,3‐butadiene with methyl, ethyl, and n‐propyl substituents was studied. The monomers were synthesized via substitution reactions of 2‐bromomethyl‐1,3‐butadiene with the corresponding dialkylamines. For each monomer the effects of the polymerization initiator, initiator concentration, and reaction temperature on the final polymer structure, molecular weight, and glass‐transition temperature (T_g) were examined. Using 2,2′‐azobisisobutyronitrile as the initiator at 75 °C, the resulting polymers displayed a majority of 1,4 microstructures. As the temperature was increased to 100 and 125 °C using t‐butylperacetate and t‐butylhydroperoxide, the percentage of the 3,4 microstructure increased. Differential scanning calorimetry indicated that all of the T_g values were lower than room temperature. The T_g values were higher when the majority of the polymer structure was 1,4 and decreased as the percentage of the 3,4 microstructure increased. The Diels–Alder side products found in the polymer samples were characterized using NMR and gas chromatography‐mass spectrometry methods. The polymerization temperature and initiator concentration were identified as the key factors that influenced the Diels–Alder dimer yield. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4070–4080, 2000     

Synthesis of photosensitive and thermosetting poly(phenylene ether) based on poly[2,6‐di(3‐methyl‐2‐butenyl)phenol‐co‐2,6‐dimethyl‐phenol] and a photoacid generator

A chemically amplified photosensitive and thermosetting polymer based on poly[2,6‐di(3‐methyl‐2‐butenyl)phenol (15 mol %)‐co‐2,6‐dimethylphenol (85 mol %)] ( 3c ) and a photoacid generator [(5‐propylsulfonyloxyimino‐5H‐thiophen‐2‐ylidene)‐(2‐methylphenyl)acetonitrile] was developed. Poly[2,6‐bis(3‐methyl‐2‐butenyl)phenol]‐co‐2,6‐dimethylphenol)] ( 3 ) with high molecular weights (number‐average molecular weight ～ 24,000) was prepared by the oxidative coupling copolymerization of 2,6‐di(3‐methyl‐2‐butenyl)phenol with 2,6‐dimethylphenol in the presence of copper(I) chloride and pyridine as the catalyst under a stream of oxygen. The structures of 3 were characterized with IR, ¹H NMR, and ¹³C NMR spectroscopy. 3 was crosslinked by a thermal treatment at 300 °C for 1 h under N₂. The 5% weight loss temperatures and glass‐transition temperatures of the cured copolymers reached around 420 °C in nitrogen and 300 °C, respectively. The average refractive index of the cured copolymer ( 3c ) film was 1.5452, from which the dielectric constant at 1 MHz was estimated to be 2.6. The resist showed a sensitivity of 35 mJ cm^?2 and a contrast of 1.6 when it was exposed to 436‐nm light, postexposure‐baked at 145 °C for 5 min, and developed with toluene at 25 °C. A fine negative image featuring 8‐μm line‐and‐space patterns was obtained on a film exposed to 100 mJ cm^?2 with 436‐nm light in the contact‐printed mode. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 149–156, 2005     

Cationic ring‐opening polymerization of novel 1,3‐dehydroadamantanes with various alkyl substituents: Synthesis of thermally stable poly(1,3‐adamantane)s

Cationic ring‐opening polymerizations of 5‐alkyl‐ or 5,7‐dialkyl‐1,3‐dehydroadamantanes, such as 5‐hexyl‐ ( 4 ), 5‐octyl‐ ( 5 ), 5‐butyl‐7‐isobutyl‐ ( 6 ), 5‐ethyl‐7‐hexyl‐ ( 7 ), and 5‐butyl‐7‐hexyl‐1,3‐dehydroadamantane ( 8 ), were carried out with super Brønsted acids, such as trifluoromethanesulfonic acid or trifluoromethanesulfonimide in CH₂Cl₂ or n‐heptane. The ring‐opening polymerizations of inverted carbon–carbon bonds in 4–8 proceeded to afford corresponding poly(1,3‐adamantane)s in good to quantitative yields. Poly( 4–8 )s possessing alkyl substituents were soluble in 1,2‐dichlorobenzene, although a nonsubstituted poly(1,3‐adamantane) was not soluble in any organic solvent. In particular, poly( 8 ) exhibited the highest molecular weight at around 7500 g mol^?1 and showed excellent solubility in common organic solvents, such as THF, CHCl₃, benzene, and hexane. The resulting poly( 4–8 )s containing adamantane‐1,3‐diyl linkages showed good thermal stability, and 10% weight loss temperatures (T₁₀) were observed over 400 °C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4111–4124     

Synthesis of α‐maleimide‐ω‐dienyl heterotelechelic poly(methyl methacrylate) and its cyclization by the intramolecular Diels–Alder reaction

The synthesis of heterotelechelic poly(methyl methacrylate) (PMMA) containing α‐maleimide‐ω‐dienyl end‐groups and its subsequent intramolecular cyclization are described. The anionic polymerization of methyl methacrylate was carried out with 3‐tert‐butyldimethylsilyloxypropyl‐1‐lithium and 5‐bromo‐1,3‐pentadiene as the initiator and terminator, respectively, to synthesize α‐hydroxy‐ω‐dienyl‐PMMA. The introduction of the maleimide group to the α chain end by the reaction of the sodium salt of the polymer with N‐(3‐chloromethylphenyl)‐maleimide or N‐(3‐bromomethylphenyl)‐maleimide was not successful because of the nucleophilic addition of alkoxide to the carbon carbon double bond of the maleimide group. When 4,4′‐bismaleimidediphenylether was allowed to react with the alkoxide, the aimed α‐maleimide‐ω‐dienyl‐PMMA was obtained in a good yield. Ring closure by the intramolecular Diels–Alder reaction was carried out by the heating of the dilute polymer solution in tetrahydrofuran. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 237–246, 2000     

Synthesis of new amphiphilic and lypophilic polymer networks containing 2‐methyl‐ and 2‐nonyl‐2‐oxazoline by the macroinitiator method

New amphiphilic and lypophilic polymer networks were obtained by the copolymerization of 2‐methyl‐2‐oxazoline (MeOXA), and/or 2‐nonyl‐2‐oxazoline (NoOXA) and 2,2′‐tetramethylenebis(2‐oxazoline) (BisOXA), respectively, initiating the copolymerization by random copolymers of chloromethylstyrene and methyl methacrylate or of chloromethylstyrene and styrene (macroinitiator method). Potassium iodide was used as an activator agent and the reaction was carried out in benzonitrile at 110 °C. In general, the polymer gels were obtained with a yield of 62 to 88%. The networks were characterized by high‐resolution magic angle spinning (HRMAS) NMR spectroscopy and by its absorption of polar and nonpolar solvents. In the case of amphiphilic polymer networks, the absorption of solvents depends on the molar ratio of 2‐methyl‐ to 2‐nonyl‐2‐oxazoline inside the polymer network favoring the absorption of polar solvents with a higher content of 2‐methyl‐2‐oxazoline. These gels showed a maximal swelling degree of 13 mL of water, 20 mL of methanol, and 13 mL of chloroform, respectively, per g of polymer. The lypophilic polymer networks containing only 2‐nonyl‐2‐oxazoline showed a maximal swelling degree of 8 mL of toluene, 14 mL of chloroform, and 2 mL of methanol, respectively, per g of the lypophilic network. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 122–128, 2005     

Temperature‐induced aggregation of the copolymers of N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate in aqueous solutions

A series of random copolymers of N‐isopropylacrylamide (NIPAM) and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulphonate (AMPS) was synthesized by free‐radical copolymerization. The content of AMPS in the copolymers ranged from 1.1 to 9.6 mol %. The lower critical‐solution temperature (LCST) of copolymers in water increased strongly with an increasing content of AMPS. The influence of polymer concentration on the LCST of the copolymers was studied. For the copolymers with a higher AMPS content, the LCST decreased faster with an increasing concentration than for copolymers with a low content of AMPS. For a copolymer containing 1.1 mol % of AMPS the LCST dropped by about 3 °C when the concentration increased from 1 to 10 g/L, whereas for a copolymer containing 9.6 mol % of AMPS the LCST dropped by about 10 °C in the concentration range from 2 to 10 g/L. It was observed that the ionic strength of the aqueous polymer solution very strongly influences the LCST. This effect was most visible for the copolymer with the highest content of AMPS (9.6 mol %) for which an increase in the ionic strength from 0.2 to 2.0 resulted in a decrease in the LCST by about 27 °C (from 55 to 28 °C), whereas for the copolymer containing 1.1 mol % of AMPS the LCST decreased only by about 6 °C (from 37 to 31 °C) when the ionic strength increased from 0.005 to 0.3. The reactivity ratios for the AMPS and NIPAM monomer pairs were determined using different methods. The values of r_AMPS and r_NIPAM obtained were 11.0–11.6 and 2.1–2.4, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2784–2792, 2001     

Synthesis and characterization of poly(4‐alkyl‐4‐methyl‐2‐azetidinone)s

Poly‐β‐amides (nylons 3) were synthesized via the anionic polymerization of a series of 4‐alkyl‐4‐methyl‐2‐azetidinones where the alkyl group is a methyl, ethyl, propyl, butyl, or pentyl. The “non‐assisted” polymerization was conducted under vacuum, in the bulk, at 160°C, using potassium 2‐pyrrolidonate as catalyst, whereas the “assisted” polymerization was carried in dimethylsulfoxide, at room temperature, using N‐acetylpyrrolidinone‐2 as activator but it gave no polymer with a propyl or bulkier side group. Side reactions occur in all cases. X‐ray spectra showed that poly(4‐alkyl‐4‐methyl‐2‐azetidinone)s are amorphous with propyl, butyl, and pentyl groups, and semi‐crystalline with methyl or ethyl substituents. Both semi‐crystalline polyamides exhibit an extended planar zigzag conformation, with a fiber identity period along the c axis of 4.9 Å. Glass transition temperatures, melting temperatures, and/or decomposition temperatures are also reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 761–769, 1999     

Organosoluble and light‐colored fluorinated polyimides from 4,4′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl and aromatic dianhydrides

A novel fluorinated diamine monomer based on 4,4′‐biphenol was synthesized via a straightforward, high‐yielding two‐step procedure. 4,4′‐Biphenol was reacted with 2‐chloro‐5‐nitrobenzotrifluoride in the presence of potassium carbonate to yield the intermediate dinitro compound, which was subsequently reduced to afford the fluorinated diamine, 4,4′‐bis(4‐amino‐3‐trifluoromethylphenoxy)biphenyl. A series of organosoluble fluorinated polyimides were prepared from the diamine with various aromatic dianhydrides via a conventional two‐step thermal imidization method. All polyimides were soluble in strong dipolar solvents such as N‐methyl‐2‐pyrrolidone and N,N‐dimethylacetamide. The polyimides showed excellent thermal and thermooxidative stability and good mechanical properties. No significant weight loss was observed below a temperature of 520 °C in nitrogen or in air, and the glass‐transition temperatures ranged from 247 to 313 °C. Low dielectric constants (2.57–3.65 at 10 kHz), low moisture absorption (0.1–0.7 wt %), and low color intensity were also observed. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 524–534, 2002; DOI 10.1002/pola.10113     

Synthesis of 9‐[2‐(2‐hydroxymethyl‐2‐methyl‐, ‐(2‐acetoxymethyl‐2‐methyl‐, ‐(2,2‐di(hydroxymethyl)‐, and ‐(2,2‐Di(acetoxymethyl)‐1,3‐dioxan‐5‐yl)ethyl] derivatives of guanine and 2‐aminopurine

Synthesis of 9‐[2‐(2‐hydroxymethyl‐2‐methyl‐, ‐(2‐acetoxymethyl‐2‐methyl‐, ‐(2,2‐di(hydroxymethyl)‐, and ‐(2,2‐di(acetoxymethyl)‐1,3‐dioxan‐5‐yl)ethyl] derivatives of guanine and 2‐aminopurine, 2–9 , has been accomplished in seven to eight step sequences from readily available 1‐(tert‐butyldiphenylsilyloxy)‐acetone, 1,3‐di(tert‐butyldiphenylsilyloxy)acetone, and the diol 10 . Formation of cyclic ketals 11 and 12 was carried out successfully under an acidic condition using a catalytic amount of methanesulfonic acid along with excess anhydrous copper(II) sulfate in toluene. Subsequent reactions of desilylation, acetylation, hydrogenolysis, and bromination afforded the key intermediates 19 and 20 , which were coupled with 2‐amino‐6‐chloropurine to produce the purine compounds 21 and 22 in good yields. Guanine derivatives 2–5 were obtained from 21 and 22 by hydrolysis and acetylation, while the dechlorination and hydrolysis of 21 and 22 yielded the 2‐aminopurine compounds 6–9 .     

Reversible 1,3‐dipolar cycloaddition of dimethyl 2‐thiono‐1,3‐dithiole‐4,5‐dicarboxylate with dimethyl acetylenedicarboxylate

It was shown that dimethyl 2‐thiono‐1,3‐dithiole‐4,5‐dicarboxylate ( 2 ) and dimethyl acetylenedicarboxylate (DMAD) undergo a 1,3‐dipolar cycloaddition to produce a short‐lived ylide intermediate ( 3 ). The 1,3‐dipolar cycloaddition took place even at room temperature, although sluggishly, but took place much more rapidly under application of a high pressure of 500 MPa. The 1,3‐dipolar cycloaddition is reversible and the ylide 3 immediately splits into 2 and DMAD. When the reaction of 2 with DMAD was carried out at room temperature without solvent, a spiro‐1,3‐dithiole ( 11 ) was formed in 11% yield, whereas the reaction at 150°C provided a thiophene derivative ( 13 ) in 41% yield. It was found that 11 undergoes a thermal rearrangement to 13 . Results of attempted chemical trapping of the ylide 3 are also reported. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:434–440, 2000