Preparation and radical ring-opening polymerization of exo-methylene substituted cyclic ketene acetals

Preparation and radical ring-opening polymerization of the exo-methylene substituted cyclic ketene acetals, 2,4-dimethylene-1,3-dioxolane ( I ) and 2,5-dimethylene-1,3-dioxane ( II ), were carried out. Ketene acetals I and II were prepared by dehydrohalogenation of the corresponding cyclic haloacetal with potassium tert-butoxide in tetrahydrofuran at –78°C and ambient temperature, respectively. I underwent radical polymerization with essentially quantitative ring-opening with di-tert-butyl peroxide in dimethylformamide at 120°C. On the other hand, II underwent both ring-opening polymerization and vinyl polymerization under the same conditions of the polymerization of I . The differences of polymerization behavior between I and II were also discussed.     

Alkylation of acetals using manganate-BF3·OEt2 mixed reagent

A mixture of `R<sub>3</sub>MnMgBr' and BF<sub>3</sub>·OEt<sub>2</sub> prepared in advance only by stirring both reagents in ether converted acetals to alkylation products, where an alkoxy group of acetals was substituted by the alkyl group of manganese reagent used. Ketals also reacted with the `mixed reagent' to afford the corresponding alkylation products in high yield. α-Alkoxy-substituted cyclic ethers and acetoxy-substituted cyclic ethers were selectively converted to ring-opening alkylation products and α-alkyl-substituted cyclic ethers, respectively.     

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.     

Synthesis and bactericidal activity of substituted cyclic acetals

A series of substituted cyclic acetals were synthesized and tested for their bactericidal activity against bacteria strain Azospirillum brasilense Sp245.     

Oligomeric Branched Polyethers with Multiple Hydroxyl Groups by Cationic Ring-Opening Polymerization for Inorganic Surface Modification

Summary: Cationic ring-opening polymerization of cyclic ethers (also esters and acetals) substituted with hydroxyl groups leads to branched multihydroxyl polymers. When 4-membered hydroxysubstituted oxetanes or 5-membered hydroxysubstuituted oxolanes (or lactone and 1,3-dioxolane) are used as monomers the polymerization products have limited molecular weights (about 1000). Polymerization of these monomers leading in situ to oligomeric products was used for inorganic surface modification. Successful polymerizations of oxetane as well as considered as difficult to polymerize 5-membered hydroxysubstituted cyclic monomers initiated from montmorillonite clay and silica nanoparticles surfaces were performed.     

Chloral Hydrate as a Water Carrier for the Efficient Deprotection of Acetals,Dithioacetals, and Tetrahydropyranyl Ethers in Organic Solvents

The efficient deprotection of several acetals, dithioacetals, and tetrahydropyranyl (THP) ethers under ambient conditions, using chloral hydrate in hexane, is described. Excellent yields were realized for a wide range of both aliphatic and aromatic substrates. The method is characterized by mild conditions (room temperatures or below), simple workup, and the ready availability of chloral hydrate. High chemoselectivity was also observed in the deprotection, acetonides, esters, and amides being unaffected under the reaction conditions. Products were generally purified chromatographically and identified spectrally. These results constitute a novel addition to current methodology involving a widely employed deprotection tactic in organic synthesis. It seems likely that the mechanism of the reaction involves adsorption of the substrate on the surface of the sparingly soluble chloral hydrate.     

环缩醛化合物在光聚合体系中的研究进展

环缩醛化合物作为一类具有光敏性的化合物,虽然在上世纪60年代有较多的研究,但由于其吸收波长较窄、引发效率较低等限制,后期研究比较少.但最近5年内,由于对胡椒环等环缩醛化合物的重新认识,尤其是将其作为光聚合引发助剂来提高引发效率或减少引发体系的毒性,获得了光聚合生物材料领域的特别关注.本文对环缩醛类化合物的光聚合行为进行了系统阐述,对当前环缩醛类化合物用作光引发剂及助引发剂的进展也进行了详细介绍.     

环状缩醛对某些含官能团烯烃的自由基加成反应

率的加成产物。这些产物通常是不易制备的,因而该反应在这一类酯的合成中将是有效的方法。结果和讨论我们应用的1和含官能团的烯烃2反应,结果列于表1。显然,在体系中存在着多个反应的竞争。要使得上述加成成为主要反应,首先要减少2的自聚和调聚反应,其次要使如下的链反应能够实现(见 p.176)。     

Synthesis of Polysubstituted γ‐Butenolides via a Radical Pathway: Cyclization of α‐Bromo Aluminium Acetals and Comparison with the Cyclization of α‐Bromoesters at High Temperature

Polysubstituted butenolides were obtained in good to high yields from α‐bromoesters derived from propargyl alcohols by a one‐pot reaction involving the radical cyclization of α‐bromo aluminium acetals, followed by the oxidation of the resulting cyclic aluminium acetals in an Oppenauer‐type process and migration of the exocyclic C?C bond into the α,β‐position. Comparison with the direct cyclization of α‐bromoesters at high temperature and under high dilution conditions is described. Deuterium‐labelling experiments allowed us to uncover “invisible” 1,5‐hydrogen atom transfers (1,5‐HATs) that occur during these cyclization processes, together with the consequences of the latter in the epimerization of stereogenic centres. Compared to the classical approach, the cyclization of aluminium acetals proved to be highly chemoselective and its efficiency was illustrated by the short total syntheses of optically enriched γ‐butenolides isolated from Plagiomnium undulatum and from Kyrtuhrix maculans.     

Reactions of cyclopropanone acetals with alkyl azides: carbonyl addition versus ring-opening pathways

The Lewis acid-mediated reactions of substituted cyclopropanone acetals with alkyl azides were found to strongly depend on the structure of the ketone component. When cyclopropanone acetal was treated with alkyl azides, N-substituted 2-azetidinones and ethyl carbamate products were obtained, arising from azide addition to the carbonyl, followed by ring expansion or rearrangement, respectively. When 2,2-dimethylcyclopropanone acetals were reacted with azides in the presence of BF3.OEt2, the products obtained were alpha-amino-alpha'-diazomethyl ketones, which arose from C2-C3 bond cleavage of the corresponding cyclopropanone, giving oxyallyl cations that were captured by azides. Aryl-substituted cyclopropanone acetals, when subjected to these conditions, afforded [1,2,3]oxaborazoles exclusively, which were also the result of C2-C3 bond rupture, azide capture, and then loss of nitrogen. In the reactions of n-hexyl-substituted cyclopropanone acetals with alkyl azides, a mixture of 2-azetidinones and regioisomeric [1,2,3]oxaborazoles was obtained. The reasons for the different behavior of the various systems are discussed.     

Synthesis and some properties of cyclic acetals of malonaldehyde

The Lewis acid-catalyzed addition of cyclic orthoformates to vinyl ethyl ether, which leads to the formation of malonaldehyde acetals, was studied. It is shown that of the linear-cyclic malonaldehyde acetals, 2-(2,2-diethoxyethyl)- and 5,5-dimethyl-2-(2,2-diethoxyethyl)-1,3-dioxanes are stable. The transacetalization of 1,1,3,3-tetraethoxypropane with 1,2- and 1,3-diols, which leads to the formation of cyclic malonaldehyde acetals, was studied. The physicochemical constants of the acetals were determined, and their ¹H and ¹³C NMR spectra are described.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 459–463, April, 1983.     

Aniline‐Promoted Cyclization–Replacement Cascade Reactions of 2‐Hydroxycinnamaldehydes with Various Carbonic Nucleophiles through In Situ Formed N,O‐Acetals

In this study, we report the harnessing of new reactivity of N,O‐acetals in an aminocatalytic fashion for organic synthesis. Unlike widely used strategies requiring the use of acids and/or elevated temperatures, direct replacement of the amine component of the N,O‐acetals by carbon‐centered nucleophiles for C?C bond formation is realized under mild reaction conditions. Furthermore, without necessary preformation of the N,O‐acetals, an amine‐catalyzed in situ formation of N,O‐acetals is developed. Coupling both reactions into a one‐pot operation enables the achievement of a catalytic process. We demonstrate the employment of simple anilines as promoters for the cyclization–substitution cascade reactions of trans‐2‐hydroxycinnamaldehydes with various carbonic nucleophiles including indoles, pyrroles, naphthols, phenols, and silyl enol ethers. The process offers an alternative approach to structurally diverse, “privileged” 2‐substituted 2H‐chromenes. The synthetic power of the new process is furthermore shown by its application in a 2‐step synthesis of the natural product candenatenin E and for the facile installation of 2‐substituted 2H‐chromene moieties into biologically active indoles.     

Preparation of acyl alkyl acetals of chloral

Conclusions The reaction of semiacetals of chloral with carboxylic acid chlorides has given acyl alkyl acetals of chloral.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1869–1871, August, 1967.     

Preparation of phosphorylated acetals of chloral

Conclusions The reaction of semiacetals of chloral with dialkyl phosphorochloridates in the presence of a base has given the corresponding phosphorylated chloral acetals. The yields of the compounds obtained amounted to 35–70%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, p. 1872, August, 1967.     

Double transacetalization of diacylium ions

A novel gas-phase reaction of diacylium ions of the O=C=X(+)=C=O type (X = N, CH) is reported: double transacetalization with cyclic acetals or ketals. The reaction is exothermic and highly efficient, and forms members of a new class of highly charged-delocalized ions: cyclic ionic diketals. Pentaquadrupole double- and triple-stage mass spectrometric (MS(2) and MS(3)) experiments reveal the high double transacetalization reactivity of O=C=N(+)=C=O and O=C=CH(+)=C=O, whereas the synthesis of differently substituted cyclic ionic diketals is performed in MS(3) experiments via sequential mono- and double transacetalization of O=C=N(+)=C=O and O=C=CH(+)=C=O with different acetals. With cyclic acetals, the acylium-thioacylium ion O=C=N(+)=C=S reacts promptly and selectively by mono-transacetalization at its acylium site, but the free thiacylium site of its cyclic ionic ketal is nearly unreactive by double transacetalization. Therefore, only the acylium site of O=C=N(+)=C=S can be efficiently protected by transacetalization. Low-energy MS(3) collision-induced dissociation of the cyclic ionic diketals of O=C=N(+)=C=O and O=C=CH(+)=C=O sequentially frees each of the protected acylium site to form the mono-derivatized ion, and then the fully deprotected diacylium ion.     

Unzipping and scrambling reaction-induced sequence control of copolymer chains via temperature changes during cationic ring-opening copolymerization of cyclic acetals and cyclic esters

A temperature change-dependent sequence transformation of copolymer chains was demonstrated by a method based on tandem depolymerization and transacetalization reactions during the cationic ring-opening copolymerization of cyclic acetals and cyclic esters. In this study, the position of polymerization-depolymerization equilibrium was controlled by the reaction temperature rather than by the decrease in monomer concentration under vacuum conditions, as in our previous study. First, the conditions for efficient copolymerization were optimized, with a particular focus on the structures of cyclic acetals and cyclic esters. Subsequently, sequence transformation induced by temperature change was examined during the copolymerization of 2-methyl-1,3-dioxepane (generated in situ from 4-hydroxybutyl vinyl ether) and δ-valerolactone using EtSO₃H. The homosequence length of cyclic acetals decreased during depolymerization (unzipping) at the oxonium chain ends upon increasing the temperature from 30 to 90 °C, while transacetalization (scrambling) of the main chain transferred midchain cyclic acetal homosequences to the oxonium chain ends. As a result of the cycle of unzipping and scrambling reactions, an alternating-like copolymer was obtained. Interestingly, the possibility of reversible sequence transformation upon heating and cooling was also demonstrated.     

Stable polymers from cyclic ketene acetals: Cationic polymerization initiated by acid-washed glassware or acid-washed glass beads

Stable polymers were made by the cationic 1,2-polymerization of cyclic ketene acetals initiated by acid-washed glassware or acid-washed glass beads. Among several reactions possible for the very reactive cyclic ketene acetals, only the corresponding acetals of polyketene were formed. These structures were demonstrated by FTIR, ¹H-NMR, and ¹³C-NMR analyses. © 1996 John Wiley & Sons, Inc.     

Cyclic Acetal-Photosensitized Polymerization. XII. Photopolymerizations of Styrene and Methyl Methacrylate in the Presence of Polycyclic Acetals

Styrene (St) and methyl methacrylate (MMA) were photopolymerized in the presence of poly-2-vinyl-1,3-dioxolane (PVDO), poly-2-vinyl-4-hydroxymethyl-1,3-dioxolane (PVHDO), or the terpolymer of vinyl formal/vinyl acetate/vinyl alcohol (PVFAcA) at 30 or 40°C. The ability to accelerate the photopolymerization increased in the order PVFAcA < PVHDO < PVDO; the ability of pendent cyclic acetal was larger than that of cyclic acetals which are not pendent. Moreover, the promoting ability per cyclic acetal increased with the increase in the number of cyclic acetal cyclic acetal group in the molecule.     

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.     

GaCl3-catalyzed insertion of isocyanides into a C-O bond in cyclic ketals and acetals

The reaction of cyclic ketals or acetals with 2,6-dibromophenylisocyanide in the presence of a catalytic amount of GaCl(3) results in the insertion of isocyanide into the carbon-oxygen bond of cyclic ketals and acetals. [reaction: see text]