Cationic polymerization of 2-vinyl-1,3-dioxane

The cationic polymerization of 2-vinyl-1,3-dioxane initiated with triethyloxonium tetrafluoroborate was studied with particular emphasis on elucidation of the structure of the polymer. The polymer was a light yellow powdery material with a molecular weight of several thousands which was soluble in most organic solvents. The infrared and NMR investigations on the polymer, together with chemical analyses, showed that the polymer consisted of the three structural units I, II, and III, the contents of which were estimated to be 5–10%, 20–25%, and 65–70%, respectively. The formation of the structural units I and II was discussed in detail.     

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.     

Polymerization of cyclic acetals. I. Polymerization of 1,3,6-trioxacyclooctane and copolymerization with p-methoxystyrene

The polymerization of 1,3,6-trioxacyclooctane initiated by trityl salts with various counterions in CH₂Cl₂ was investigated. The reaction mixtures and the isolated polymers were analyzed by GPC (double detection—IR and UV at 254 nm),¹H-, and¹³C-NMR spectroscopy. In the early stage of polymerization only oligomers (mainly cyclic) were formed. With longer reaction times, linear polymers (yield 86–94%, M = 70,000–80,000) were obtained. The concentration of each individual oligomer passed through a maximum and decreased, reaching its equilibrium concentration. The time interval necessary to reach the maximum concentration increased with n. The total concentration of the oligomers was 0.2 mol L^?1 regardless of the initiator used. Conditions for polymerization with virtually no termination were found. Addition of p-methoxystyrene to the “living” polyacetals resulted in block copolymers. GPC,¹H- and ¹³C-NMR and acidolytic degradation were used to prove the formation of AB block copolymers. The reactive alkoxycarbenium growing species are responsible for the formation of block polyacetal-polymethoxystyrene copolymer.     

Kinetics and mechanism of bromination of cyclic acetals with 1,4-dioxane dibromide

It is shown that the reactivities of cyclic formals in the case of bromination with dioxane dibromide increase in the order 1,3-dioxepane > 1,3-dioxalane 1,3-dioxane, which is explained not only by steric factors but also by the ease of cleavage of the C₄-O₃ bond of the dioxacyclane ring. The bromination of cyclic acetals takes place through prior enolization of the cyclic acetal with subsequent electrophilic addition of bromine to the double bond.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 176–179, February, 1981.     

Polymerization of cyclic acetals. II. Synthesis of amphiphilic block copolymers

The sequential copolymerization of 1,3,6-trioxacyclooctane (TOC) and 1,3-dioxolane (DOL) (B) with various vinyl monomers (A) was investigated. Under appropriate conditions amphiphilic block copolymers of the type AB and ABA were formed. The reaction mixtures and the isolated polymers were analyzed by GPC (double detection—IR and UV at 254 nm), IR, ¹H-, and ¹³C-NMR spectroscopy. Block copolymers with chosen molecular weights and low polydispersity could be obtained only by sequential copolymerization of p-methoxystyrene on “living” TOC. In the polymerization of DOL with α-methylstyrene and i-butyl vinyl ether (IBVE) transfer reactions take place to a larger degree.     

Cationic copolymerization of 2-methylene-5,5-dimethyl-1,3-dioxane with 2-methylene-1,3-dioxolane and 2-methylene-1,3-dioxane

Copolymers of the cyclic ketene acetals, 2-methylene-5,5-dimethyl-1,3-dioxane, 3 , (M₁) with 2-methylene-1,3-dioxolane, 4 , (M₂) or 2-methylene-1,3-dioxane, 5 , (M₂), were synthesized by cationic copolymerization. An experimental method was designed to study the reactivity of these very reactive and extremely acid sensitive cyclic ketene acetal monomers. The reactivity ratios, calculated using a computer program based on a nonlinear minimization algorithm, were r₁ = 6.36 and r₂ = 1.25 for the copolymerization of 3 with 4 , and r₁ = 1.56 and r₂ = 1.42 for the copolymerization of 3 with 5. FTIR and ¹H-NMR spectra when combined with the values of r₁ and r₂ showed that these copolymers were formed by a cationic 1,2-polymerization (ring-retained) route. Furthermore the tendency existed to form very short blocks of M₁ or M₂ within the copolymers. Cationic copolymerization of cyclic ketene acetals have the potential to be used for synthesis of novel polymers. © 1996 John Wiley & Sons, Inc.     

Rotamere 2-Phenyl-1,3-dioxane

By means of dipole moment measurements, NMR-spectroscopical methods and force field calculations of o-, m- and p-substituted 2-phenyl-1,3-dioxanes a systematic study concerning the rotameric behaviour of the phenyl group was performed.In o-substituted 2-phenyl-1,3-dioxanes the preferred conformation of the phenyl ligand was found to be displaced about 60 degs. from thecisoid-bisectional conformer. Introduction of an additional substituent in the second o-position gives rise to a change in the rotameric state, the preferred conformation now being bisectional. In contrast, the barriers resisting rotation about the C_ar–C-2-bond in 2-phenyl-1,3-dioxane and its m- and p-substituted derivates turn out to be much lower. Thus at room temperature an ensemble of approximately bisectional rotamers exists.The conformations and rotational barriers determined are discussed in terms of non bonded and dipole-dipole interactions.

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6. Mitt.:H. Lehner, Mh. Chem.107, 565 (1976).     

Synthesis and characterization of acrylated phosphonates and their polymers having 1,3-dioxolane and 1,3-dioxane moieties derived from brominated cyclic acetals of polyols through the Arbuzov reaction. II

Glycerol, D -mannitol, and D -sorbitol were converted into their mono- and di-O-1,3-dioxolane and 1,3-dioxane bromoethylidene derivatives through a transacetalation reaction with bormoacetaldehyde diethyl acetal under controlled conditions. These brominated dioxolane or dioxane derivatives were subsequently phosphonylated through the Arbuzov reaction. The phosphonylated cyclic acetals were used as precursors for the synthesis of acrylated phosphonate monomers. All these compounds have been characterized by elemental analysis and spectroscopic (IR, ¹H-,¹³C-, ³¹P-NMR and mass) methods. A mixture of 1,3-dioxane and 1,3-dioxolane derivatives was obtained with D -sorbitol, whereas the reaction products with glycerol and D -mannitol yielded primarily the 1,3-dioxolane derivatives. The acrylated phosphonates of glycerol and mannitol have been polymerized and studied on the basis of gel permeation chromatography and their spectral and thermal properties. The acrylated phosphonates, monomers, and polymers, were shown to have a large capacity to solvate and dissolve heavy metal salts. This results in a dramatic increase (> 100°C) of the glass transition temperature of these polymers.     

Polymers of 2-vinyl-1,3-dioxolanes

Lewis acid-initiated polymerizations of 2-vinyl-1,3-dioxolanes have been studied. Evidence is presented showing at least three types of structural units in the polymer. Polymerization is propagated by 1,2 addition, by acetal ring opening, and by rearrangement, ring opening mechanisms. Polymerization is accompanied by the formation of a dimer consisting of a 1,4-dioxepane and 1,3-dioxolane ring. Film formers from methacrylate esters of vinyl dioxolane compounds are also described.     

Ring-opening reactions of cyclic acetals and 1,3-oxazolidines with halosilane equivalents

Reactions of acetal and 1,3-oxazolidine rings were examined using two kinds of iodosilane equivalent reagents, a 1:2 mixture of Me3SiNEt2 and MeI (reagent 1a) and a 1:1 mixture of Et3SiH and MeI containing a catalytic amount of PdCl2 (reagent 1b). In the reactions of alkanone ethylene acetals with reagent 1a, a C-O bond in the acetal ring readily cleaved to give 2-(trimethylsiloxy)ethyl enol ethers. Similarly, the C-O bond of 1,3-oxazolidine rings cleaved to give ring-opened imine or enamine derivatives. The reactions of aromatic ketone ethylene acetals and cyclohexanone trimethylene acetal led to deprotection of the acetal unit to liberate free ketones. With reagent 1b, cycloalkanone ethylene acetal afforded a dimeric product with 2-iodoethyl alkenoate moieties, while aromatic ketone ethylene or trimethylene acetals produced deprotected ketones.     

Cationic ring-opening polymerization of 2-isopropenyl-4-methylene-1,3-dioxolane

Preparation and cationic ring-opening polymerization of 2-isopropenyl-4-methylene-1,3-dioxolane ( VI ) was performed. Unsaturated cyclic acetal VI was prepared by dehydrochlorination of 2-isopropenyl-4-chloromethyl-1,3-dioxolane, which was easily obtained from methacrolein and epichlorohydrin, with sodium methoxide at ambient temperature. The cationic polymerization of VI with BF₃OEt₂ or CF₃SO₃H at ?78°C afforded only crosslinked polymers, whereas the polymerization by CH₃SO₃H gave soluble poly(keto-ether) which consisted of units VII containing an isopropenyl group in the side chain and units VIII containing a carbon-carbon double bond in the main chain. The reaction of VI with ethanethiol in the presence of protic acid was also carried out as a model reaction of the polymerization. The reaction initiated by the addition of proton to the 4-methylene group of VI , and quantitative ring-opening isomerization followed by the addition of ethanethiol afforded acyclic ketone IX and X . On the basis of the model reaction, the polymerization mechanism is also discussed. © 1993 John Wiley & Sons, Inc.     

Novel catalytic rearrangements of 2-vinyl-1,3-thiazetidines

The thiazetidines (1) and (2) undergo a novel and high yielding rearrangement on hydrogenation with heterogeneous catalysis to give the thiazolidines (5) and (8) whilst reaction with the homogeneous catalyst Rh(Ph₃P)₃Cl results in the alternative high yielding rearrangement to give a thiazine.     

Lactam and amide acetals. 52. Reaction of dimethylformamide diethylacetal with 2,2-dimethyl-4,6-dioxo-1,3-dioxane (Meldrum's acid)

Depending on the conditions of carrying out the reaction of dimethylformamide diethylacetal with the Meldrum's acid, either 2,2-dimethyl-4,6-dioxo-5-(N,N-dimethyl-aminomethylene)-1,3-dioxane or N,N,N¹N¹-tetramethylformamidinium salt of 2,2-dimethyl-4,6-dioxo-5-(2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-yl)methylene-1,3-di-oxane are formed. The two compounds can react with primary amines to form N-substituted 2,2-dimethyl-4.,6-dioxo-5-aminomethylene-1,3-dioxanes.For Communication 51, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 184–187, February, 1988.     

Synthesis of amino sugars via isoxazolines DL- and D-lividosamine (2-amino-2,3-dideoxy-ribo-hexose) derivatives from 4-vinyl-1,3-dioxolanes and nitroacetaldehyde acetals

1,3-Dipolar cycloaddition of nitrile oxides, generated from nitroethanol and nitroacetaldehyde derivatives 3, 21 and 22, respectively, and of benzonitrile oxide to 4-vinyldioxolanes 1, 2 gave ca 4:1 erythro/threo mixtures of corresponding isoxazolines. LAH reduction of erytho isoxazolines proceeded with similar (ca 4:1) selectivity to furnish protected ribo-amino-polyols 11, 15,19, DL- and D-lividosamines 31 and 33, respectively, as main products. The DL-lividosamine derivative 33 was obtained pure by crystallization. In the D-series, the corresponding ribo/arabino mixture D-31/D-32 was transformed to the known α-methyl D-lividosaminide D-37.     

Comparative conformational analysis of 1,3-dioxane and 1,3-dithiane

It was shown by ab initio quantum-chemical approximations HF/6-31G(d) and MP2/6-31G(d)//HF/6-31G(d) that the conformational isomerization of 1,3-dioxane and 1,3-dithiane proceeded along common routes. The potential energy surface of both compounds contains six minima including the chair invertomers and enantiomeric flexible forms. They are separated by several potential barriers. It was established by molecular dynamics method that the flexible conformers at heating and keeping at 295–300 K transformed into each other and in the chair conformer.     

Liquid-crystalline derivatives of 1,3-dioxane

Some 5-(2-pentyl-1,3-dioxanyl) 4-(4-substituted benzylidenamino)benzoates with smectic and nematic liquidcrystalline properties have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 759–760, June, 1993.     

Studies on the copolymerization of unsaturated 1,3-dioxane derivatives—IV. Radical copolymerization of 2-furyl-5,5-dimethyl-1,3-dioxane with maleic anhydride

The copolymerization of 2-furyl-5,5-dimethyl-1,3-dioxane with maleic anhydride in the presence of a radical catalyst yields equimolar, alternating copolymers in which the furyl units have 2,5-linkage. It has been shown that 2-furyl-5,5-dimethyl-1,3-dioxane forms a charge transfer complex with maleic anhydride. The equilibrium constant for the complex was determined by NMR spectroscopy.