4- Methylene-1,3-dioxolanes

Of the 4-methylene-1,3-dioxolanes reported thus far (Table 4.6), only the 2,2-diphenyl derivative (50) is reported to give the polyketone quantitatively (Scheme 4.32). This requires temperatures in excess of 120 °C in bulk polymerization."... 

Table 4.6 Extent of Ring-Opening During Polymerizations of 4-Methylene-1,3-dioxolane and 2-Methylene-1,4-dioxane Derivatives...

Styryl- or 2-vinyl-substituted 4-methylene-1,3-dioxolanes rearrange (Equation 41) simply by heating (80-150°C, preferably 120°C, 3—48 h) to 4,5-dihydrooxepin-3(2//)-ones <1994TL3111>. 

Lithium allenolates are obtained from 2,2-dimethy 1-4-methylene- 1,3-dioxolane and 2 equiv. of i-bu-tyllithium. These allenolates can further undergo aldol reactions (Scheme 21).71... 

The radical ring-opening elimination polymerization of 4-methylene-l,3-dioxolane stimulated us to construct a novel template polymerization (3). The concept is that polymers bear polymers. Polymer-supported monomer, which had a structure of 2,2-dipheny 1-4-methylene-1,3-dioxolane, reacted with radical species to afford polyketone and copolymer of styrene with vinylbenzophenone as newborn polymer and template, respectively (Figure 12). These polymers were easily separated by fractional precipitation without any particular chemical treatment after polymerization. On the other hand, common template polymerization requires annoying procedures for the separation of obtained polymers form template. On this point, our novel template polymerization system differs from conventional template polymerization. 

Hydroxytetrahydrofurans. Triisobutylaluminum acts both as a Lewis acid to catalyze the isomerization of 4-methylene-1,3-dioxolanes to 2-oxotetrahydrofurans (via C-O bond cleavage and C-C bond formation) and as a reducing agent for the ketone group of the intermediate. The 4-methyIene-1,3-dioxolanes are available by a Tebbe olefination. 

Poly(2-trichloromethyl-4-methylene-1,3-dioxolane-alt-MA), 321, 327 Poly(trimethylallylsilane-alt-MA), 311 Poly(2,4,4-trimethyl-l-pentene-alt-MA), 338, 586 properties, 433, 436... 

The radical polymerization behaviors of 4-methylene-1,3-dioxolane involve three polymerization modes (Scheme 27) The first one is the chain-growth radical... 

Methylene-1,3-dioxolane refluxed 10 hrs. with ethylene glycol 4-methyl-1,3-dioxole. Y almost 100%. - Ethylene glycol acts as general acid catalyst. F. e. s. A. Kankaanpera, T. Launosalo, and P. Salomaa, Acta Ghem. Scand. 20, 2622 (1966). 

Co-polymerizations and homo-polymerizations of monomers such as dienes or 4-methylene dioxolan, in which two or more types of ion may propagate simultaneously, are further examples of enieidic polymerizations. These dienes, of course, also provide examples of eniedic radical and anionic polymerizations. Indeed the idea of dieidic polymerization has been suggested by several authors in relation to anionic polymerizations it arose from the aggregation in solution of the lithium alkyls [135], and similar phenomena. 

There has been a report on the synthesis and utilization of an cvo-methylene dioxolane bearing styryl group (Scheme 28). The styryl group can be used for the copolymerization with other... 

It is stated in the basic patent that ethylene oxide (II) and 1.3-dioxolane (III) are the preferred materials. By the occasional incorporation of molecules containing two successive methylene groups the tendency of the molecules to unzip is markedly reduced. 

Tabic 4.5 Extent of Ring-opening During Polymerizations of 2-Methylene-l,3-dioxolane and Related Species... 

The monomer 2 can be regarded as a 2,4-disubstituted-1,3-dioxolane, and the thermodynamic parameters for the polymerization may be compared with those for the polymerization of 1,3-dioxolane in methylene chloride21. ... 

In Entry 11 the dienophile is an a-methylene lactam. As noted for this class of dienophiles, the stereoselectivity results from preferred exo addition (see p. 471). The reaction in Entry 12 was used in an enantiospecific synthesis of estrone. The dienophile was used in enantiomerically pure form and the dioxolane ring imparts a high facial selectivity to the dienophile. The reaction occurs through an endo TS. 

Dimethyl-4-methylene-l,3-dioxolan-2-one reacts with isonitriles in the presence of a palladium catalyst to afford iminofurans (Equation (121)).480 Successive insertion of isonitriles to the carbon-palladium bond of 7r-allylpalladium intermediate is postulated. 

The 125 mL stainless steel autoclave was flushed with nitrogen. The 5-methylene-l,3-dioxolane-2-one, the ruthenium catalyst and dichloromethane (10 mL) were placed in the autoclave under a nitrogen atmosphere. 

A new heterocyclic system, 3 ,4-dihydro-3//-benzo[4,5]imidazo[l,2-f]oxazol-l-one 462, was synthesized by reaction of 4,4-dimethyl-5-methylene-l,3-dioxolan-2-one with o-phenylenediamine in the presence of copper bromide as catalyst in carbone dioxide at 60-80 °C under high pressure (Equation 217) <1999CHC216>. 

Scheme 3.—Proposed Mechanism for Photochemieally Initiated, Radical Addition of 1,3-Dioxolane to 3-Deoxy-l,2 5,6-di-0-isopropylidene-3-C-methylene-a-D-riho-hexo-furanose (5).

Studies on the polymerization of various 4-methylene-l,3-dioxolans [94] by BF3Et20 or A1C13 showed that 4-methylene-l,3-dioxolan itself polymerises mainly through the double bond the 2-methyl and 2,2-dimethyl compounds gave polymers with a variable carbonyl content. This arises from a co-polymerization in which units of type (VII) and (VIII) are incorporated in the chain in different proportions, according to the reaction conditions ... 

Studies of the kinetics of the polymerisation of 1,3 dioxolan and of the depolymerisation of its polymer by perchloric acid in methylene dichloride have been accompanied by measurements of the electrical conductivity of the reaction mixtures [23]. These have shown that ions are present during the reactions and the evidence strongly suggests that they are essentially concerned in these. This is one of the very few direct demonstrations of the participation of ions. 

Materials 1,3-Dioxolane (1) and 1,3-dioxepane (5) were prepared and purified conventionally. Compound 1 contained no impurities detectable by GLC, but 5 contained a trace of tetrahydrofuran (THF) which could not be removed even by distillation on a Fenske column with a reflux ratio of 50 1 4-methyl-l,3-dioxolane (4) was prepared by Astle s method [10]. All monomers were dried preliminarily by storage over LiAlH4 in reservoirs attached to a conventional high-vacuum line fitted only with all-metal valves, and then stored with liquid Na-K alloy until used. Methylene dichloride was purified conventionally, distilled on a Normatron 1.5 m column, dried i.vac. over LiAlH4 on a conventional high-vacuum line, and then stored for 24 h over a fresh sodium film immediately before use, in a reservoir attached to the vacuum line. 

The first two compounds have dipole moments which do not lie in the H—C-H plane. The C-2 methylene in (3) is geometrically similar to the methylene in (2) and is similarly substituted. However, in the dioxolane the permanent dipole moment must lie in or close to the H-C-H plane. The solvent invariance of VH H in (i) and (2) in contrast to the solvent dependence of 2/H H in (3) (Table 22) provides some support for this hypothesis. 

For this reason, a reinvestigation of the cyclic ketene acetal, 2-methylene-l,3-dioxolane (I), that had been prepared by McElvain and Curry (14) was undertaken. Although McElvain and Beyerstedt (15) reported that benzoyl peroxide had no appreciable effect on diethyl ketene acetal, no such study was reported (14) for the 2-methylene-l,3-dioxolane (I). The synthesis was carried out as follows (6) ... 

A very special type of template polymerization was presented by a group of Japanese scientists. The method used was based on the observation that during radical polymerization of 2,2-diphenyl-4-methylene-l,3-dioxolane, elimination of benzophe-none occurs according to reaction ... 

Very interesting results were published in respect of application of copolymers of 4-methylene-2-phenyl-2-(4-vinylphenyl)-l,3 dioxolane with styrene as a template ... 

The infrared spectra of l,4-anhydro-3,5-0-methylene- and -2-0-methyl-DL-xylitol have been studied.60 The 2-methyl ether was obtained by converting l,4-anhydro-3,5-0-methylene-DL-xylitol into its monomethyl ether, and then hydrolyzing off the methylene group. A methyl ether prepared from the known l,4-anhydro-3,5-0-isopro-pylidene-2-O-methyl-DL-xylitol proved to be identical with this compound, thus establishing at the same time that the methylene group in the known acetal is attached to 0-3 and 0-5 of 1,4-anhydro-DL-xylitol. The methylene group, having a 1,3-dioxolane structure, was characterized by an absorption band at about 2800 cm 1. 

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