Synthesis and radical ring-opening polymerization behavior of vinylcyclopropane bearing six-membered cyclic acetal moiety

Synthesis and radical ring-opening polymerization of vinylcyclopropane bearing six-membered cyclic acetal moiety, 1-vinyl-4,8-dioxaspiro[2.5]octane (1), were carried out. 1 was prepared by the reaction of 1,1-dichloro-2-vinylcyclopropane and 1,3-propanediol in DMF in the presence of a base. Radical polymerization of 1 was carried out in the presence of an appropriate initiator (3 mol % vs. 1) at 60 and 120°C in degassed sealed ampoules for 20 h. A colorless transparent viscous polymer was obtained by the isolation with preparative HPLC. The structure of poly(1) was determined to consist of two 1,5-ring-opened units and a unit bearing no olefinic moiety. The difference of the activation energies for the ring-opening reaction of the cyclopropane ring calculated by the molecular orbital method could explain the selectivity in the direction of the cleavage of the cyclopropane ring. Acid hydrolysis of poly(1) afforded the corresponding polyketone in quantitative conversion. © 1996 John Wiley & Sons, Inc.     

Investigation of reactions of the organozinc reagents prepared from zinc and dialkyl dibromomalonates with the derivatives of 2-arylmethyleneindan-1,3-dione and 5-arylmethylene-2,2-dimethyl-1,3-dioxane-4,6-dione

Organozinc compounds prepared from dialkyl dibromomalonates and zinc react with 2-arylmethyl-eneindan-4,6-diones, 5-arylmethylene-2,2-dimethyl-1,3-dioxane-4,6-diones, as well as with 2-[4-(1,3-dioxoindan-2-ylidenemethyl)phenyl]methyleneindan-1,3-dione and 5-[4-(2,2-dimethyl-4,6-dioxo-1,3-dioxane-2-ylidenemethyl)phenyl]methylene-2,2-dimethyl-1,3-dioxane-4,6-diones to form dialkyl 3-aryl-1′3′-dioxaspiro(cyclopropane-2,2′-indan)-1,1-dicarboxylates, dimethyl 3-aryl-6,6-dimethyl-5,7-dioxa-4,8-dioxaspiro[2,5]octan-2,2-dicarboxylates, dialkyl 2-{4-[3,3-bis (alkoxycarbonyl)-1′,3′-dioxaspiro(cyclopropane-2,2′-indan)-1-yl]phenyl}-1′,3′-dioxaspiro[cyclopropane-2,2′-indan]-1,1-dicarboxylates, and dialkyl 2-{4-[2,2-bis(alkoxycarbonyl)-6,6′-dimethyl-4,8-dioxo-5,7-dioxaspiro[2,5]oct-1-yl]phenyl}-6,6-dimethyl-4,8-dioxo-5,7-dioxaspiro[2,5]octan-1,1-dicarboxylate respectively.     

Reduction of the shrinkage of thermosets by the cationic curing of mixtures of diglycidyl ether of bisphenol A and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione)

Ytterbium and lanthanum triflates were used as initiators to cure mixtures of diglycidyl ether of bisphenol A and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione) in several proportions. The evolution of the epoxy and 6,6‐dimethyl‐(4,8‐dioxaspiro[2.5]octane‐5,7‐dione) bands during curing and the linear ester groups in the final materials were evaluated with Fourier transform infrared in the attenuated‐total‐reflection mode. The use of a conventional cationic initiator, boron trifluoride monoethylamine, was also studied to test the advantages of lanthanide triflates. The shrinkage after curing and the thermal degradability of the materials with variations in the comonomer ratio and the initiator were evaluated and related to the chemical structure of the final network. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6869–6879, 2006     

On the structure of compounds obtained from the reaction of amines with 6,6-dimethyl-5,7-dioxaspiro[2.5]octane-4,8-dione

Recent literature data on the reaction of aromatic amines with 6,6-dimethyl-5,7-dioxaspiro[2.5]octane-4,8-dione need to be corrected.     

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     

Reactions of 6,6-dialkyl-5,7-dioxo-4,8-dioxaspiro[2.5]octane-1,1,2,2-tetracarbonitriles with O-centered nucleophiles

The reactions of 6,6-dialkyl-5,7-dioxo-4,8-dioxaspiro[2.5]octane-1,1,2,2-tetracarbonitriles with primary aliphatic alcohols lead to the formation of alkyl 2,2,3,3-tetracyanocyclopropanecarboxylates; the reactions of the same compounds with ketone oximes give 2-amino-4,4-bis(alkylideneaminooxy)-6-(alkylidene-aminooxycarbonyl)-3-azabicyclo[3.1.0]hex-2-ene-1,5-dicarbonitriles, while with aldehyde oximes 2-amino-2-oxo-1,5-dicyano-3-azabicyclo[3.1.0]hex-2-ene-6-carboxylic acid is formed.     

Esr studies of the ring opening of cyclopropane radical cations in freon matrices

The radical cations of cyclopropane and several of its methyl derivatives have been characterized by ESR spectroscopy following their generation by γ irradiation of dilute solutions of the parent compounds in Freon matrices at 77 K. In the CFCl₃, CF₃CCl₃, and CF₂ClCCl₃, matrices, only the ring-closed species is usually observed in the accessible temperature range up to ca 160 K. In the CFCl₂CF₂Cl matrix, however, the ring-closed radical cations initially formed at 77 K undergo ring opening between 83 and 110 K, the more highly substituted radical cations requiring a higher temperature for this transformation. The ring-closed radical cations are ²A₁ species for C_2v symmetry, the most substituted cyclopropane C-C bond being elongated with the spin density largely confined to the basal carbons in a face-to-face (90°, 90°) structure. In the ring-opened radical cations, the radical center is localized on the most substituted carbon atom following the breaking of the weakened C-C bond of the ring-closed species. The radical conformations of the ring-opened species have been determined, the RCH₂CH₂· center produced from cyclopropane having a bisected conformation while the RCH₂CMe₂· center obtained from 1,1,2,2-tetramethylcyclopropane is eclipsed, as expected for the presence of α-methyl substituents at the radical site. The nature of the putative carbocation center in the ring-opened radical cations is discussed with reference to recent proposals that this center is strongly coordinated to an electrophile (Cl^- or RCl) thereby negating the requirement for an orthogonal structure. Consideration of the strong matrix dependence of the ring-opening reaction suggests a possible solvation effect, however, in which the CFCl₂CF₂Cl matrix assists the twisting of one of the CR₁R₂ groups at the most substituted bond, leading to the rupture of this one-electron σ bond. A strong solvation effect also explains why ring-opening can occur in a suitable polar solvent despite theoretical calculations of unfavourable energetics for a similar gas-phase reaction. Experiments are also described on spiro[2.5]octane, the cyclopropane ring undergoing scission at the CH₂-CH₂ bond of this radical cation to give an RCH₂· radical center. this radical then undergoes a H-atom abstraction with a neutral spiro[2.5]octane molecule in the CFCl₂CF₂Cl matrix at higher temperature to give the spiro[2.5]oct-6-yl radical.     

Reactions of bromine-containing organozinc compounds derived from α,α-dibromo ketones with 2-arylmethylideneindan-1,3-diones and 5-arylmethylidene-2,2-dimethyl-1,3-dioxane-4,6-diones

Bromine-containing organozinc compounds generated from 1,1-dibromo-3,3-dimethylbutan-2-one reacted with 2-arylmethylideneindan-1,3-diones and 5-arylmethylidene-2,2-dimethyl-1,3-dioxane-4,6-diones to give 3-aryl-2-(2,2-dimethylpropanoyl)spiro[cyclopropane-1,2′-indan]-1′,3′-diones and 1-aryl-6,6-dimethyl-2-(2,2-dimethylpropanoyl)-5,7-dioxaspiro[2.5]octan-4,8-diones, respectively. Reactions of 2-arylmethylideneindan-1,3-diones with bromine-containing zinc enolates derived from 1-aryl-2,2-dibromopropan-1-ones and 2,2-dibromo-1,2,3,4-tetrahydronaphthalen-1-one resulted in the formation of 2-aroyl-3-aryl-2-methylspiro-[cyclopropane-1,2′-indan]-1′,3′-diones and 2,3: 8,9-dibenzo-12-phenyldispiro[4.0.5.1]dodecane-1,4,7-trione, respectively.     

Kinetics of the thermal decomposition of 1,2-dioxaspiro[2,5]octane

The products and kinetics of the thermolysis of 1,2-dioxaspiro[2,5]octane in cyclohexanone and cyclohexanone-CCl₄ mixtures are studied. 1,2-Dioxaspiro[2,5]octane is consumed via two parallel routes: isomerization to oxepan-2-one and solvent (cyclohexanone) oxidation with the partial escape of radicals from the cage (17% at 25 °C). Under an inert atmosphere, the alkyl radicals formed by solvent oxidation initiate the chain radical decomposition of 1,2-dioxaspiro[2,5]octane. The mechanism of 1,2-dioxaspiro[2,5]octane thermolysis is discussed on the basis of the results obtained. The activation parameters of 1,2-dioxaspiro[2,5]octane isomerization to oxepan-2-one and reactions of dioxaspiro[2,5]octane with cyclohexanone are discussed.     

贫电子环丙烷衍生物与甲醇的反应

顺-1-呋喃乙酰基-2-对位取代苯基-6,6-二甲基-5,7-二氧-螺-[2,5]-4,8-辛二酮和顺-1-噻吩乙酰基-2-对位取代苯基-6,6-二甲基-5,7-二氧-螺-[2,5]-4,8-辛二酮与甲醇于封管中80℃反应72 h得到β-呋喃甲酰基-γ-甲氧基-γ-对取代苯基-丁酸甲酯及β-噻吩甲酰基-γ-甲氧基-γ-对取代苯基-丁酸甲酯,其结构经1H NMR,13C NMR,IR,MS及APT。讨论了反应机理。     

Hydrolysis of 6,6-dimethyl-4,8-dioxo-5,7-dioxaspiro[2.5]octane-1,1,2,2-tetracarbonitrile

Hydrolysis of 6,6-dimethyl-4,8-dioxo-5,7-dioxaspiro[2.5]octane-1,1,2,2-tetracarbonitrile in aqueous dioxane in the presence of hydrogen bromide gave a mixture of 2,2,3,3-tetracyanocyclopropane-1-carboxylic acid and ammonium 3-cyano-4-dicyanomethylidene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate. Hydrolysis of the same compound in the presence of sulfuric acid was accompanied by nitrogen migration and led to the formation of (1R*,2S*,3S*)-1,3-dicyanocyclopropane-1,2-dicarboxamide whose structure was proved by X-ray analysis.     

A stereoselective synthetic route to 1,6-Dioxaspiro[4.4]non-3-en-2-ones from cyclopropyl alkyl ketones and alpha-ketoesters

[reaction: see text] The SnCl(4)-mediated reactions of cyclopropyl alkyl ketones with alpha-ketoesters afford a novel method for the synthesis of 1,6-dioxaspiro[4.4]non-3-en-2-ones with high stereoselectivities in moderate to good yields. This process is a sequential reaction involving a nucleophilic ring-opening reaction of the cyclopropane by H(2)O, an aldol-type reaction, and a cyclic transesterification mediated by Lewis acid.     

Synthesis of highly functionalised enantiopure bicyclo[3.2.1]- octane systems from carvone

The commercially available monoterpene carvone has been efficiently converted into the tricyclo[3.2.1.0(2.7)]octane and bicyclo[3.2.1]octane systems characteristic of some biologically active compounds. The sequence used for this transformation involves as key features an intramolecular Diels-Alder reaction of a 5-vinyl-1,3-cyclohexadiene and a cyclopropane ring opening.     

Polymerization systems driven by aromatization energy: Anionic polymerization of 4-allylidene-2,6-dimethyl-2,5-cyclohexadien-1-one and spiro[2,5]octadienone derivatives

To investigate the polymerization systems driven by aromatization energy, 4-allylidene-2,6-dimethyl-2,5-cyclohexadien-1-one ( Ia ), 5,7-dimethyl-1-vinylspiro[2,5]octa-4,7-dien-6-one ( Ib ), 4,7-dimethyl-1-vinylspiro[2,5]octa-4,7-dien-6-one [ Ic ], 2-vinyl-2′-methylspiro[cyclopropane-1,4′-(1′-naphthalenone)] ( Id ), and 2-phenyl-2′-methylspiro[cyclopropane-1,4′-(1′-naphthalenone)] ( Ie ) were prepared and polymerized with sodium cyanide in N,N-dimethylformamide. Monomer Ia was highly polymerizable even at ?65°C. Monomers Ib–Ie also polymerized well, giving powdery polymers that were soluble in common solvents. All the polymerizations took place through the aromatization of the cyclohexadienone ring, suggesting that the aromatization energy is the driving force for the polymerization of these monomers.     

Synthesis and cationic photopolymerization of monomers based on nopol

Starting with nopol [(R)‐(−)‐2‐(2′‐hydroxyethyl)‐6,6‐dimethyl‐8‐oxatricyclo[3.1.1.1^2,3]octane, I] as a substrate, two new, interesting monomers, allyl nopol ether epoxide III and nopol 1‐propenyl ether epoxide IV, were prepared. The photoinitiated cationic polymerizations of these two monomers as well as several other model compounds were studied using real‐time infrared spectroscopy. Surprisingly, the rates of epoxide ring‐opening polymerization of both monomers were enhanced as compared to those of the model compounds. Two different mechanisms which involve the free radical induced decomposition of the diaryliodonium salt photoinitiator were proposed to explain the rate acceleration effects. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1199–1209, 1999     

New construction of the bicyclo[3.3.1]nonane system via Lewis acid promoted regioselective ring-opening reaction of the tricyclo[4.4.0.0]dec-2-ene derivative

A new access to the bicyclo[3.3.1]nonane system, which is a common structure in a number of polyisoprenylated phloroglucinol derivatives (phloroglucins), has been developed via the Lewis acid promoted regioselective ring-opening reaction of the cyclopropane, a tricyclo[4.4.0.0^5,7]dec-2-ene derivative.     

ESI‐MS Studies on Alcoholysis Mechanism of Electron‐deficient Cyclopropane Derivatives

Electrospray ionization mass spectrometry (ESI‐MS) was utilized to perform monitoring of the intermediates in the reaction of 1,2,3‐trisubstituted electron‐deficient cyclopropane derivatives, cis‐1‐thien‐2′‐oyl‐2‐(p‐subustituted phenyl‐6,6‐dimethyl)‐5,7‐dioxaspiro[2.5]‐4,8‐octadiones, with methanol. Key intermediates, either cationic or protonated forms of neutral species, were intercepted and characterized by ESI‐MS and its tandem version (ESI‐MS/MS). Therefore, the mechanism of the ring‐opening process for electron‐deficient cyclopropane derivatives was fully confirmed by the intermediates monitored.     

Recent Advances in Free-Radical Ring-Opening Polymerization

Although cyclic ketene acetals, such as 2-methylene-1, 3-dioxepane, undergo quantitative free-radical ring-opening polymerization, their reactivity in copolymerization is rather low. In order to find a series of monomers that have high reactivities in copolymerization and still undergo free radical ring-opening polymerization, a series of cyclic acrylates was synthesized and polymerized. For example, β-bromolactic acid condensed with benzaldehyde to give a cyclic acetal lactone which on treatment with base gave the cyclic acrylate. Free-radical solution polymerization at 140°C of the cyclic acrylate, which produced a benzyl radical upon ring opening, gave quantitative ring opening. However, in bulk at 120°C, only 20% of the rings were opened during poiymerization. The resulting polymers containing the pyruvate ester units were shown to be highly biodegradable with microorganisms. Vesicles containing these cyclic acrylates on the end of one of the hydrophobic chains of the lipidlike molecules were shown to undergo free-radical ring-opening polymerization to give polymerized vesicles which were biodegradable. In order to discover groups other than carbonyl groups and strained rings that would promote free-radical ring-opening polymerization, a series of spiromethylenecyclohexadienes were prepared and polymerized. Thus, 3-methylenespiro [5,5] undeca-1,4-diene in bulk at 130°C gave a polymer in which 79% of the rings had opened and in solution at 130°C gave a polymer in which nearly all of the rings had opened. A benzo derivative, 3-methylene-8,9-benzo [5,5] undeca-1,4,8-triene, gave a polymer that is essentially an alternating copolymer of p-xylylene and o-xylylene and has a very high thermal decomposition temperature. A tricyclic dispirocyclohexadiene derivative was shown to undergo double free-radical ring-opening polymerization to give a polymer with expansion in volume containing a p-phenylene group in the backbone.     

Cationic polymerizations of substituted 2-methylene-1,3-dioxocyclic acetals, 2-methylene-1,3-dithiolane and copolymerization of 2-methylene-1,3-dithiolane with 4-(t-butyl)-2-methylene-1,3-dioxolane1

Carbon black-supported sulfuric acid or BF₃·Et₂O-initiated polymerizations of 2-methylene-4,4,5,5-tetramethyl-1,3-dioxolane (1), 2-methylene-4-phenyl-1,3-dioxolane (2), and 2-methylene-4-isopropyl-5,5-dimethyl-1,3-dioxane (3) were performed. 1,2-Vinyl addition homopolymers of 1–3 were produced using carbon black-supported H₂SO₄ initiation at temperatures from 0°C to 60°C whereas both ring-opened and 1,2-vinyl structural units were present in the polymers using BF₃·Et₂O as an initiator. Cationic polymerizations of 2-methylene-1,3-dithiolane (4) and copolymerization of 4 with 2-methylene-4-(t-butyl)-1,3-dioxolane (5) were initiated with either carbon black-sulfuric acid or BF₃·Et₂O. Insoluble 1,2-vinyl addition homopolymers of 4 were obtained upon initiation with the supported acid or BF₃·Et₂O. A soluble copolymer of 2-methylene-1,3-dithiolane (4) and 4-(t-butyl)-2-methylene-1,3-dioxolane (5) was obtained upon BF₃·Et₂O initiation. This copolymer is composed of three structural units: a ring-opened dithioester unit, a 1,2-vinyl-polymerized 1,3-dithiolane unit, and a 1,2-vinyl polymerized 4-(t-butyl)-1,3-dioxolane unit. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2823–2840, 1999     

A novel redox reaction between 8-aza-5,7-dimethyl-2-trifluoromethylchromone and alkyl mercaptoacetates

[reaction: see text] 8-Aza-5,7-dimethyl-2-trifluoromethylchromone reacts with alkyl mercaptoacetates to give pyrido derivatives of 2-oxa-7-thiabicyclo[3.2.1]octane, which undergo the reductive ring-opening to sulfanyl acetates. The latter compounds are useful CF(3)-containing building blocks for the preparation of a variety of 2-pyridone derivatives.