THE EFFECTS OF MONOMER STRUCTURE OF CYCLIC KETENE ACETALS ON THE BEHAVIOR OF CONTROLLED RADICAL RING-OPENING POLYMERIZATION

Polymerization of three cyclic ketene acetals: i.e., 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), 2-methylene-4-phenyl-1,3-dioxolane (MPDO) and 4, 7-dimethyl-2-methylene-1, 3-dioxepane(DMMDO) were carried out in the presence ofethyl α-bromobutyrate/CuBr/2, 2'-bipyridine respectively. The structures of poly(BMDO), poly(MPDO) and poly(DMMDO)were characterized by ~1H and ~(13)C-NMR spectra. The effects of monomer structure on the behavior of atom transfer freeradical ring-opening polymerization were investigated and the mechanism of controlled free radical ring-openingpolymerization was discussed.     

Cationic copolymerization of 2-vinyl-1,3-dioxane with styrene and 1,3-dioxolane

Copolymerization of 2-vinyl-1,3-dioxane with styrene and 1,3-dioxolane was carried out in methylene chloride at 0°C with triethyloxonium tetrafluoroborate as an initiator. Random copolymers were obtained from both of these monomer pairs, but attempted copolymerization of 2-vinyl-1,3-dioxane with 3,3-bis(chloromethyl)oxetane under similar conditions resulted in the homopolymer of the latter monomer. There were three structural units of 2-vinyl-1,3-dioxane in these copolymers as in its homopolymer: the “ester” unit, which was formed by vinyl addition with hydride shift followed by ring-opening rearrangement, the “vinyl” unit produced by ring-opening reaction, and the unit with a pendant 1,3-dioxane ring formed by simple vinyl addition. The fractions of the ester and vinyl units to the total 2-vinyl-1,3-dioxane units in the copolymer of 2-vinyl-1,3-dioxane with styrene decreased with decreasing 2-vinyl-1,3-dioxane content. On the contrary, the fraction of the vinyl unit in the copolymer of 2-vinyl-1,3-dioxane with 1,3-dioxolane increased slightly with decreasing 2-vinyl-1,3-dioxane content, while that of the ester unit decreased. The reactivities of the propagating species are discussed on the basis of these results.     

Lewis acid-mediated highly regioselective SN2-Type ring-opening of 2-aryl-N-tosylazetidines and aziridines by alcohols

Lewis acid-mediated highly regioselective SN2-type ring-opening of 2-aryl-N-tosylazetidines with alcohols to afford various 1,3-amino ethers in excellent yields with good enantiomeric excess is described. Similar SN2-type ring-opening of chiral 2-phenyl-N-tosylaziridine with various alcohols produces the corresponding nonracemic 1,2-amino ethers in excellent yields and good ee. The mechanism of the ring-opening of aziridines and azetidines via an SN2 pathway is supported by the formation of nonracemic amino ethers.     

Imidazopyridinium and pyridopyrimidium bromides: synthesis and hydrolysis

The reactions of symmetrical and unsymmetrical 2,2'-dipyridylamines with 1,2-dibromoethane and 1,3-dibromopropane give imidazopyridinium and pyridopyrimidium bromides, respectively. These acetone/CH(2)Cl(2)-insoluble, highly fluorescent quaternary ammonium salts undergo addition/ring opening upon treatment with methanolic KOH to give pyridin-2-one derivatives. A sequential N,N-dialkylation/ring-opening hydrolysis/N,N-dialkylation/ring-opening hydrolysis strategy was developed for the construction of unsymmetrical bis(pyridin-2-ones).     

Preparation and radical ring-opening polymerization of 2-substituted-4-methylene-1,3-dioxolanes

2-Methyl-2-phenyl-4-methylene-1,3-dioxolane ( IIa ), 2-ethyl-2-phenyl-4-methylene-1,3-dioxolane ( IIb ), 2-phenyl-2-(n-propyl)-4-methylene-1,3-dioxolane ( IIc ), 2-phenyl-2-(i-propyl)-4-methylene-1,3-dioxolane ( IId ), 2-(n-heptyl)-2-phenyl-4-methylene-1,3-dioxolane ( IIe ), 2-methyl-2-(2-naphthyl)-4-methylene-1,3-dioxolane ( IIf ), and 2,2-diphenyl-4-methylene-1,3-dioxolane ( IIg ) were prepared and polymerized in the presence of a radical initiator. IIa–IIf were found to undergo vinyl polymerization with ring-opening reaction accompanying the elimination of ketone groups in bulk. IIg was found to undergo the quantitative ring-opening reaction accompanying the elimination of benzophenone in solution to obtain polyketone without any side reaction.     

Unexpected nitrilimine cycloaddition of thiazolo[3,2-a]pyrimidine derivatives

1,3-Dipolar cycloaddition of 2-arylidene-6,7-dihydro-5H-thiazolo[3,2-a]pyrimidine-3(5H)-ones to diphenylnitrilimine (generated in situ by triethylamine dehydrohalogenation of the N′-phenylbenzohydrazonoyl chloride) proceeded regio- and site-selectively affording a mixture of two unexpected isomer products at reflux temperature. The cycloaddition/ring-opening/rearrangement/substitution, mechanism of the reaction was also discussed.     

Dual Behavior of Ammonium Acetate for the Synthesis of Diverse Symmetrical/Unsymmetrical Bis[1,3]oxazines Possessing Anticancer Activity

A simple and efficient approach was developed to synthesize symmetrical/unsymmetrical bis[1,3]oxazines using ammonium acetate with controllable substitution patterns in a one-pot fashion. In a representative crystal structure, the [1,3]oxazine ring is in a distorted semichair conformation with C2-carbon and nitrogen atoms residing above and below the naphthalene plane, leading to strain in the ring that allows ring-opening polymerization to take place. A few of the derivatives were found to possess anticancer activity. This current modest protocol affords numerous advantages such as mild reaction condition, shorter reaction time, operational simplicity, and excellent yield.     

Single-component catalyst/initiators for the organocatalytic ring-opening polymerization of lactide

The synthesis and characterization of a series of primary and secondary alcohol adducts of 1,3-dimesitylimidazolin-2-ylidene is described. These adducts are stable as solids at room temperature, but readily release alcohol and the free carbene in solution. These alcohol adducts function as excellent single-component catalyst/initiators for the ring-opening polymerization of lactide under mild conditions, providing polymers with controlled molecular weights and narrow polydispersities. Multifunctional adducts were used to prepare poly(lactide)s of more complex architectures.     

Synthesis and reactivities of 10-S-3 trithiadiazapentalene derivatives

1,3-Bis(p-substituted-phenylthiocarbamoyl)-2-imidazolidinethiones 3a-f reacted with bromine to give trithiadiazapentalene derivatives 5a-f , bearing the exocyclic C-N double bonds, in moderate yields. The molecular structure of 5b was elucidated by the X-ray crystallographic analysis. The treatment of 5b-f with hydrochloric acid gave the ring-opening products, 1,3-bis(p-substituted-phenylthiocarbamoyl)-2-imidazo-lidinones 9b-f , accompanied by the production of elemental sulfur. Reduction of 5b , 5d , and 5e with sodium borohydride gave the ring-opening compounds, 1,3-bis(p-substituted-phenylthiocarbamoyl)-2-imidazolidines 13b , 13d , and 13e respectively.     

2-亚甲基-1,3-二氧己烷衍生物的合成及自由基开环聚合

本文报道了四种2-亚甲基-1,3-二氧己烷类单体:4-甲基-2-亚甲基-1,3-二氧己烷(Ⅱ)、4,6-二甲基-2-亚甲基-1,3-二氧己烷(Ⅳ)、5,5-二甲基-2-亚甲基-1,3-二氧己烷(Ⅵ)和5,5-二乙基-2-亚甲基-1,3-二氧己烷(V Ⅲ)的合成以及自由基开环聚合。结果表明,上述单体在聚合过程中出现异构化开环现象。Ⅲ和Ⅳ的甲基位置在环上氧原子的α-碳原子上时,显示对异构化反应的影响比Ⅵ及Ⅷ的甲基和乙基在β-碳原子上时更显著。上述现象与异构化开环形成仲碳自由基中间体的倾向更大有关。 Ⅳ在苯溶液中及过氧化二叔丁基存在下,120℃反应,得到全部是聚-δ-戊内酯骨架结构的聚合物。提出了一种合成聚-δ-戊内酯类链结构的聚酯的新的途径和方法。     

Generation of acyloxyketenes from unstable mesoionic 1,3-dioxolium-4-olates and their reaction with ketenophiles to give [2 + 2] cycloadducts

Fast ring opening of mesoionic 1,3-dioxolium-4-olates, generated by Rh(2)(OAc)(4)-catalyzed decomposition of phenyldiazoacetic anhydride derivatives, to acyloxyphenylketenes was demonstrated by trapping the ketenes with several ketenophiles. Reactions of phenyldiazoacetic anhydride derivatives with several ketenophiles such as dihydrofuran, carbodiimides, and imines were carried out. No 1,3-dipolar cycloadducts of the latter with 1,3-dioxolium-4-olates were observed. Instead, only their [2 + 2]-cycloadducts with the acyloxyketenes generated by ring-opening of the initially formed 1,3-dioxolium-4-olates were isolated. In the reaction with cyclopentadiene, 1,3-dipolar cycloadducts with 1,3-dioxolium-4-olates were formed as main products along with the [2 + 2]-ketene adduct. PM3 calculation of heats of formation of 2,5-diphenyl-1,3-dioxolium-4-olate and the corresponding benzoyloxyphenylketene indicates that the ring-opened acyloxyketenes are ca. 9 kcal/mol more stable than the corresponding 1,3-dioxolium-4-olates.     

Copolymerization of cyclic ketene N,O-acetals with phenylisothiocyanate via zwitterionic intermediates

The reaction of 3-methyl-2-methylene-1,3-oxazolidine ( 1a ) and phenylisothiocyanate (PhNCS) gives 3-methyl-2-(phenylthiocarbamoyl)methylene-1,3-oxazolidine ( 3 ) whereas that of 2-isopropylidene-3-methyl-1,3-oxazolidine ( 1b ) and PhNCS gives 1:1 alternating copolymers. It is assumed that the reaction of 1b and PhNCS forms a zwitterionic intermediate ( 2b ), followed by the successive combination of 2b to give 1:1 alternating copolymers 4 and/or 5 . Consequently, it was demonstrated that the copolymerization of 1b and PhNCS proceeds via a zwitterionic mechanism with complete ring-opening to afford the 1:1 alternating copolymer 5 .     

An approach to synthesis of (Z)-2-chloro-1,3-diarylpropen-1-ones by Vilsmeier reagent (bis-(trichloromethyl) carbonate/DMF)

A series of(Z)-2-chloro-1,3-diarylpropen-1-ones were unexpectedly synthesized in moderate yields by treatment of easily available 2,3-epoxy-1,3-diarylpropan-1-ones with Vilsmeier reagent,which was derived from bis(trichloromethyl) carbonate(BTC, triphosgene) and DMF.A possible mechanism was also proposed,where sequential ring-opening,halogenation and elimination reactions were involved.     

Evidence for a nucleophilic anti-attack on the cleaved C(2)-oxygen bond in Cl2AlH-catalyzed ring-opening of 2-substituted 1,3-dioxolanes

The Cl₂AlH-mediated ring-opening of 2-substituted cis-4-methyl-5-trifluoromethyl-1,3-dioxolanes was found to occur with regioselective cleavage of the O1-C2 bond by attack of the aluminum hydride from the direction anti to the departing oxygen. This stereochemical outcome, which appears to be unprecedented in the reductive cleavage of chiral acetals by aluminum reagents, is interpreted on the basis of theoretical calculations.     

Ring-opening reactions of 2-alkoxy-3,4-dihydropyrans with thiols or thiophenols

An electrophilic ring-opening reaction of 2-alkoxy-3,4-dihydropyran with a thiophenol or thiol is developed for the first time. The generated product contains not only a 1,3-dicarbonyl moiety but also a fragment of bis(alkylthio)methane. A possible mechanism is also proposed on the basis of postulating a ring-opening monotransthioacetalization product, which was prepared by using LiBr as catalyst as an intermediate.     

Preparation of vinyl alkanedithioates

S-vinyl dithioesters are prepared by ring-opening of 2-alkylidene-1,3-dithiolanes in basic medium.     

A novel and facile synthesis of 2-oxo-1,2-dihydropyridine-fused 1,3-diazaheterocycles via heterocyclic ketene aminals and Konevenagel adducts formed by phthalic anhydride and ethyl cyanacetate

An efficient synthetic pathway to 2-oxo-1,2-dihydropyridine-fused 1,3-diaza heterocycles from heterocyclic ketene aminals,phathalic anhydride and ethyl cyanacetate was established.This protocol involved aza-ene reaction/imine-enamine tautomerization/enamine-ester exchange/ring-opening reaction sequence.     

Réaction du n-bromosuccinimide sur les aryl-2 dioxolannes-1,3 d'eroulement de la réaction

Reaction of NBS with 1,3-dioxolanes fused to a bicyclo[2.2.1] skeleton involves two intermediates, the dioxolanylium ion and the 2-succinimido-1,3-dioxolane. Evidence is presented that the unusual stability of the former ionic species is due to the steric hindrance towards endo attack by bromide ion, thus leading to the succinimido compound which by action of hydrobromic acid formed insitu, yields the former ionic species which finally gives the dioxolane ring-opening products. Some factors influencing the efficiency of the NBS reaction with hindered dioxolanes are pointed out.     

Selective C−C Coupling of Vinyl Epoxides with Diborylmethide Lithium Salts

Vinyl epoxides and styrene oxide can react with diborylmethide lithium salts through an exclusive S_N2 borylmethylation/ring opening in a regio- and diastereoselective way, depending on the nature of the substrate. The ring-opening protocol provides homoallylboronates that can be transformed into challenging diastereomeric bishomoallylic alicyclic 1,3-diols. Unprecedented 3-borylated 1,2-oxaborolan-2-ol products were prepared by borylmethylation/ring opening of 2-methyl-2-vinyloxirane followed by intramolecular cyclization.     

Anionic ring-opening polymerization behavior of a seven-membered cyclic carbonate; 1, 3-dioxepan-2-one

Anionic ring-opening polymerization of a seven-membered cyclic carbonate, 1,3-dioxepan-2-one ( 1 ), was carried out to observe that the higher the polymerization temperature and lower the initial monomer concentration were, the lower the yield and molecular weight, and wider the molecular weight distribution of the obtained polymers were. The back-biting reaction and the formation of cyclic oligomers of 1 were observed during the polymerization of 1 . The relative polymerization rate of 1 was about 35 times faster than that of six-membered carbonate, 1,3-dioxan-2-one ( 3 ). The ΔHps of 1 and 3 estimated by MO (PM3) calculations were −9.8 and −4.4 kcal/mol, respectively. 1 could easily undergo the ring-opening polymerization based on larger ring strain. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1375–1380, 1997