The use of carbon black-supported sulfuric acid to initiate the cationic polymerization of cyclic ketene acetals

Stable polymers were made by the cationically initiated 1,2-polymerization of cyclic ketene acetals employing heterogeneous, activated carbon-supported sulfuric acid catalysts. A methodology has been established for the preparation of the carbon black of different acidic strengths. By adjusting either the acid strength or the amount of carbon black used, cyclic ketene acetals with different activities can be polymerized efficiently to form stable high molecular weight polymers. This methodology will be a useful tool for polymerization, copolymerization, and studies of the relative reactivities of the cyclic ketene acetals. The polymer structures were determined by FTIR, ¹³C-NMR, and ¹H-NMR studies. © 1996 John Wiley & Sons, Inc.     

Ketene acetal monomers: Cationic photopolymerization

A study of the photoinduced cationic polymerization of a novel series of cyclic and acyclic ketene acetal monomers was carried out. It was observed that the cyclic monomers underwent facile cationic polymerization to give high molecular weight polymers while the acyclic ketene acetals did not. Thermally induced polymerization was also observed on standing catalyzed by glass surfaces. Photoinduced cationic polymerizations employing both diaryliodonium and triarylsulfonium salt photoinitiators were studied. It was observed that the position and type of substitutents in the cyclic ketene acetals was the major factor in determining the proportion of vinyl and ring-opening polymerizations that take place. © 1996 John Wiley & Sons, Inc.     

Ketene acetal monomers: Synthesis and characterization

A new, facile, and high-yield synthesis of ketene acetals derived from readily available and inexpensive starting materials has been developed. For example, an α,β-unsaturated aldehyde can be condensed with an alkane diol to afford a 2-vinyl substituted cyclic acetal. This latter compound can be converted to the desired cyclic ketene acetal by isomerization of the double bond in the presence of tris(triphenylphosphine)ruthenium(II) dichloride. Good to excellent yields of cyclic ketene acetals were obtained employing this method. The novel monomers were fully characterized by IR, NMR, and by elemental analysis. © 1996 John Wiley & Sons, Inc.     

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.     

Ring opening during the cationic polymerization of 2-methylene-1,3-dioxepane: Cyclic ketene acetal initiation with sulfuric acid supported on carbon

The stable cyclic ketene acetal, 2-methylene-1,3-dioxepane, 7, has been polymerized cationically in pentane, CH₂Cl₂ and THF at 25°C to form a polymer which is composed of both ring-opened (40–50%) and ring-retained (50–60%) structures. Initiation was catalyzed by using H₂SO₄-supported on activated carbon black. This unique outcome differs significantly from the cationic polymerization of several other five- and six-membered ring cyclic ketene acetals which gave 100% 1,2-vinylpolymerization under these conditions. As the polymerization temperature increased in cationic polymerization of 7 the ring-opened content increased and the molecular weight of the polymers decreased in such solvents as cyclohexane, 1,2-dichloroethane, dimethoxyethane, and bis-(2-methoxyethyl) ether. The mechanism of this polymerization is discussed. This research also illustrated the ability to initiate the cationic polymerization of cyclic ketene acetals by acidified carbon black while avoiding subsequent polymer decomposition. © 1997 John Wiley & Sons, Inc.     

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.     

13C NMR study of the structures of some acyclic and cyclic ketene acetals

A ¹³C NMR study of the spatial structures of some acyclic and cyclic ketene acetals (for example, ketene dimethyl acetal and 2-methylene-1,3-dioxolane) has been carried out. The conclusions obtained are based on observation of the effect of structural changes on the ¹³C NMR chemical shift of the β carbon on the ketene moity. Since the extent of p-π conjugation and hence the ¹³C chemical shift of this carbon depend on the spatial orientation of the alkoxy groups about the O-C(sp²) bonds, the shift concerned may be used as a measure of the planarity of the system. The most stable retamers of ketene dimethyl acetal are s-cis,s-cis (planar) and s-cis,gauche (slightly nonplanar), in the order of decreasing stability. For ketene dialkyl acetals, the relative stability of the planar s-cis,s-cis form decreases with increasing bulkiness of the alkyl groups, but at least for primary and secondary alkyl groups, the s-cis,s-cis rotamer appears to be the most favored species. The conformations of 5- to 8-membered cyclic ketene acetals are discussed and compared with those of the corresponding cyclic vinyl ethers and hydrocarbons.     

A dipole moment study of the structures of some ketene acetals

The dipole moments of several acyclic and cyclic ketene acetals have been determined in benzene solution at 293 K using the Halverstadt-Kumler method. For ketene dialkyl acetals (alkyl = Me, Et) the results point to a predominance of the s-cis,s-trans retamer, which disagrees with the conclusions drawn previously from ¹³C NMR chemical shift data, i.e. the s-cis,s-cis form is the more stable species. In the case of 2-methoxyfuran, the dipole moment measurements confirm the previous findings based on the ¹³C NMR spectra, viz the s-cis form is the predominating rotamer. The dipole moments and structures of some other ketene acetals are also discussed.     

THEORETICAL INVESTIGATION OF KETENE BONDING MODES IN BIS(PHOSPHINE) PALLADIUM KETENE COMPLEXES

Abstract

Theoretical studies were carried out on a series of bis(phosphine) palladium ketene complexes (PR₃)₂Pd(CH₂=C=O), and on the related CH₂=C=O and Pd(PR₃)₂ molecular fragments in order to investigate the electronic structure and the bonding of the ketene ligand to the metal fragment in these complexes. An analysis of the frontier MOs has been performed in order to understand the interactions between the ketene and the metal fragments. The calculated results have shown that the η²-(C,C) mode is preferred over the η²-(C,O) mode by 10–15 kcal/mol in bis(phosphine) palladium ketene complexes. The basicity and bulkiness of the phosphine ligands PR₃ have little effect on the bonding mode in (PR₃)₂Pd(CH₂=C=O) complexes. The most stable structure was calculated to be the η²-(C,C) square planar geometry with the CH₂ group of ketene out of the molecular plane. Comparison and discussion between the two bonding modes were also presented in this paper.     

Mapping the characteristics of the radical ring‐opening polymerization of a cyclic ketene acetal towards the creation of a functionalized polyester

Radical ring‐opening polymerization of cyclic ketene acetals is a means to achieve novel types of aliphatic polyesters. 2‐methylene‐1,3‐dioxe‐5‐pene is a seven‐membered cyclic ketene acetal containing an unsaturation in the 5‐position in the ring structure. The double bond functionality enables further reactions subsequent to polymerization. The monomer 2‐methylene‐1,3‐dioxe‐5‐pene was synthesized and polymerized in bulk by free radical polymerization at different temperatures, to determine the structure of the products and propose a reaction mechanism. The reaction mechanism is dependent on the reaction temperature. At higher temperatures, ring‐opening takes place to a great extent followed by a new cyclization process to form the stable five‐membered cyclic ester 3‐vinyl‐1,4‐butyrolactone as the main reaction product. Thereby, propagation is suppressed and only small amounts of other oligomeric products are formed. At lower temperatures, the cyclic ester formation is reduced and oligomeric products containing both ring‐opened and ring‐retained repeating units are produced at higher yield. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4587–4601, 2009     

α—羰基烯酮式环二硫代缩醛类化合物的制备

从具有α-亚甲基的酮出发,利用溶液稀释的方法,提高了用Dieter法合成α-羰基烯酮式环二硫代缩醛类化合物的产率,并用改进方法合成了4个该类化合物。     

a -Oxo Ketene Dithioacetals Chemistry-A Facile Route to the Synthesis of Fused Heterocyclic Compounds

The fused heterocyclic compounds 2 : imidazo [1,2-a] pyridine 2a-c and pyrido [1,2-a] pyrimidine 2d were obtained from the reaction of a -cinnamoyl ketene dibenzylthio acetals 1 with diamine. When a -cinnamoyl -a '-benzoyl ketene N, N-acetals 3a-b were treated by t-BuONa/t-BuOH solution, 8- benzoyl-pyrido[1,2-a] pyrimidine 4 was produced.     

Novel Cyanoketene N,S‐Acetals and Pyrazole Derivatives using Potassium 2‐Cyanoethylene‐1‐thiolates

Novel ketene N,S‐acetals 3 were readily prepared by the reaction of cyanoacetamide or cyanothioacetamide with phenylisothiocyanate in the presence of potassium hydroxide, followed by alkylation of the produced salts with methyl iodide. The reaction of compounds 3 with hydrazines afforded different substituted pyrazoles 6.     

Cationic polymerization of cyclic ketene acetals via zwitterion formation with cyanoallene

This article deals with the polymerization of the cyclic ketene acetals (CKAs) 2‐methylene‐4‐phenyl‐1,3‐dioxolane (2), 2‐methylene‐4‐phenyl‐1,3‐dioxane (3), 4,7‐dimethyl‐2‐methylene‐1,3‐dioxepane (4), 2‐ethylidene‐4‐phenyl‐1,3‐dioxolane (5), 2‐phenylmethylene‐1,3‐dioxolane (6), and 2‐isopropylidene‐4‐phenyl‐1,3‐dioxolane (7) in the presence of cyanoallene (1). For 2 and 3, the homopolymerization of the CKAs proceeded without ring opening, and the number‐average molecular weights of the obtained polymers depended on the feed ratio of 1. However, the reactions of 1 with 4–7 afforded no polymers but did afford spirocyclic 1 : 1 adducts possessing cyclobutane rings. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2075–2081, 2000     

BF3·OEt2-initiated polymerization of 2-methylene-1,3-dioxepanes

BF₃·OEt₂-initiated polymerizations of 2-methylene-1,3-dioxepane gave polymers composed of both ring-retained and ring-opened structures. The ring-opening content increased with an increase in polymerization temperature. Poly(4,7-dimethyl-2-methylene-1,3-dioxepane) propagated slower during BF₃·OEt₂-initiated polymerization and had a lower ring-opened content than poly(2-methylene-1,3-dioxepane). The type of acid initiator used also affected the amount of ring opening observed. Stronger acids gave less ring opening. Attempted BF₃·OEt₂-initiated copolymerizations of these seven-membered ring cyclic ketene acetals with isobutyl vinyl ether at room temperature resulted in formation of the two homopolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 873–881, 1998     

Straightforward access to tetrahydropyridine and piperidine-fused fluorolactones from pyridines and bis(trimethylsilyl)ketene acetals

The interaction of bis(trimethylsilyl)ketene acetals with various pyridines provides a direct, general, diastereoselective access to fluorolactones via the formation of dihydropyridine-substituted carboxylic acids. These in turn reacted with selectfluor as the source of electrophilic fluorine. Whereas a discrimination of the double bonds devoid of fluorine and those bearing fluorine was observed in the case of electrophiles such as iodine, bromine and peracids, no such differentiation took place in the case of selectfluor since, besides 3,5-difluorolactones, the formation of gem-difluorolactones also took place. Moreover, the formation of two stereoisomeric fluorolactones during the lactonization of tetrahydropyridine-substituted carboxylic acids, obtained upon the interaction of (trimethylsilyl)ketene acetals with the previous lactones, could be ascribed to conformational modifications. In all the cases examined a trans, diaxial addition of the electrophile and of the carboxylate is observed. The stereochemical outcome of these reactions was assessed both by NMR spectroscopy and by X-ray crystallography.     

Polyesters by a Radical Pathway: Rationalization of the Cyclic Ketene Acetal Efficiency

Radical ring-opening polymerization (rROP) of cyclic ketene acetals (CKAs) combines the advantages of both ring-opening polymerization and radical polymerization thereby allowing the robust production of polyesters coupled with the mild polymerization conditions of a radical process. rROP was recently rejuvenated by the possibility to copolymerize CKAs with classic vinyl monomers leading to the insertion of cleavable functionality into a vinyl-based copolymer backbone and thus imparting (bio)degradability. Such materials are suitable for a large scope of applications, particularly within the biomedical field. The competition between the ring-opening and ring-retaining propagation routes is a major complication in the development of efficient CKA monomers, ultimately leading to the use of only four monomers that are known to completely ring-open under all experimental conditions. In this article we investigate the radical ring-opening polymerization of model CKA monomers and demonstrate by the combination of DFT calculations and kinetic modeling using PREDICI software that we are now able to predict in silico the ring-opening ability of CKA monomers.     

Hydroalumination of Thioacetylenes: A Versatile Generation and Reactions of α-Aluminate Sulfides Intermediates

Hydroalumination of thioacetylenes using DIBAL-H and lithium di-(isobutyl)-n-(butyl)-aluminate hydride (Zweifel's reagent), followed by addition of water, furnished exclusively the (Z)- and ( E )-vinyl sulfides, respectively. The regio- and stereochemistry of the intermediates generated, (Z)- and ( E )-phenylthio vinyl alanates, were determined by capture with iodine, which afforded the corresponding ( E )- and (Z)-1-iodo-1-phenylthio-2-organoyl ethenes. Reactions of the ( E )-iodo(thio)ketene acetals with n-BuLi followed by addition of hexanal afforded the (Z)-phenylthio allylic alcohol, while the (Z)-iodo(thio)ketene acetals under similar reactions conditions gave the ( E )-phenylthio allylic alcohol exclusively.     

A Metal-Metal Bonded Dinuclear Ruthenium Ketene Complex

We report the synthesis of metal-metal bonded dinuclear ruthenium ketene complex [CpRu(CO)]₂(μ-CH₂CO)(μ-CO), 3 , (Cp=η⁵-C₅H₅) which contains the unique structural feature, of a μ-η²(C,C) ketene group bridging two metal centers. Complex 3 is prepared by a rare intramolecular CO insertion to the methylene group of a Ru complex [CpRu(CO)₂]₂(μ-CH₂), 1 , in the absence of CO or any donor ligand. The cis and trans isomers of 3 originating from the arrangement of the Cp groups and the unsymmetrically bridging ketene group, are observed in the NMR spectra. Unlike a ketene complex without a metal-metal bond [CpRu(CO)₂]₂(μ-CH₂CO), 2 , complex 3 exhibits the chemistry of a ketene molecule and might be used as a stoichiometric ketene precusor in organic reactions.     

Polyesters by a Radical Pathway: Rationalization of the Cyclic Ketene Acetal Efficiency

Radical ring‐opening polymerization (rROP) of cyclic ketene acetals (CKAs) combines the advantages of both ring‐opening polymerization and radical polymerization thereby allowing the robust production of polyesters coupled with the mild polymerization conditions of a radical process. rROP was recently rejuvenated by the possibility to copolymerize CKAs with classic vinyl monomers leading to the insertion of cleavable functionality into a vinyl‐based copolymer backbone and thus imparting (bio)degradability. Such materials are suitable for a large scope of applications, particularly within the biomedical field. The competition between the ring‐opening and ring‐retaining propagation routes is a major complication in the development of efficient CKA monomers, ultimately leading to the use of only four monomers that are known to completely ring‐open under all experimental conditions. In this article we investigate the radical ring‐opening polymerization of model CKA monomers and demonstrate by the combination of DFT calculations and kinetic modeling using PREDICI software that we are now able to predict in silico the ring‐opening ability of CKA monomers.