1.3- Dioxanes oxetanes

Some monomers with no tendency toward homopolymerization are found to have some (not high) activity in copolymerization. This behavior is found in cationic copolymerizations of tetrahydropyran, 1,3-dioxane, and 1,4-dioxane with 3,3-bis(chloromethyl)oxetane [Dreyfuss and Dreyfuss, 1969]. These monomers are formally similar in their unusual copolymerization behavior to the radical copolymerization behavior of sterically hindered monomers such as maleic anhydride, stilbene, and diethyl fumarate (Sec. 6-3b-3), but not for the same reason. The copolymerizability of these otherwise unreactive monomers is probably a consequence of the unstable nature of their propagating centers. Consider the copolymerization in which M2 is the cyclic monomer with no tendency to homopolymerize. In homopolymerization, the propagation-depropagation equilibrium for M2 is completely toward... 

The ring-opening polymerization of cyclic ethers having 3-, 4-, and 5-membered rings (e.g., epoxides, oxetanes, THF) yields polymeric ethers. Six-membered rings (1,4-dioxane) are not capable of polymerization. 

Most of the work reported with these complexes has been concerned with kinetic measurements and suggestions of possible mechanisms. The [Ru(HjO)(EDTA)] / aq. HjOj/ascorbate/dioxane system was used for the oxidation of cyclohexanol to cw-l,3-cyclohexanediol and regarded as a model for peroxidase systems kinetic data and rate laws were derived [773], Kinetic data were recorded for the following systems [Ru(Hj0)(EDTA)]702/aq. ascorbate/dioxane/30°C (an analogue of the Udenfriend system cyclohexanol oxidation) [731] [Ru(H20)(EDTA)]70j/water (alkanes and epoxidation of cyclic alkenes - [Ru (0)(EDTA)] may be involved) [774] [Ru(HjO)(EDTA)]702/water-dioxane (epoxidation of styrenes - a metallo-oxetane intermediate was postulated) [775] [Ru(HjO)(EDTA)]7aq. H O /dioxane (ascorbic acid to dehydroascorbic acid and of cyclohexanol to cyclohexanone)... 

K. Capek and T. Vydra, Oxirane-oxetane-l,4-dioxane anhydro-ring migration in sucrose derivatives, Carbohydr. Res., 168 (1987) C1-C4. 

Cleavage of oxetanes and oxolanes.1 The reaction of LiAlH4 with diphenyl diselenide in dioxane provides a particularly active form of LiSeC6H3, which cleaves... 

Some further details of the mechanisms of photo-equilibration and fragmentation of cholest-5-en-3/3-o and -4-en-3/3-ol have been elucidated by the use of a variety of aromatic compounds as sensitizers.249 Reaction is favoured by use of phenolic compounds which can associate with the reactant. Fragmentation, which leads via the unsaturated aldehyde (314) to the oxetan (315), is particularly favoured by the presence of phenol, with dioxan as solvent, and is most efficient with the 4-en-3/3-oI. 

Three modes of reaction of aldehydes with allylsilane bearing sterically demanding silyl substituents are mediated by the proper choice of Lewis acid (Eq. 39) [66a]. Thus, influenced by SnC, allyl-t-butyldimethylsilane reacts with aldehyde in 2 1 stoichiometry to afford a ketone derivative. In contrast, use of BF3 OEt2 leads to the formation of a 1,3-dioxane derivative, which is a 1 2 adduct. Furthermore, ZrCU-pro-moted [2 -r 2] cycloaddition of allylsilane and aldehyde fnmishes oxetanes in good yields [66b]. 

The fluorescent behavior, following optical excitation, of some liquid cyclic ethers, in particular p-dioxane and its solutions, has been studied by Hirayaraa et al. (183) and Halpern and Ware (184). Product studies on cyclic ethers are still in a preliminary state. There is a brief study by Pitts and co-workers (91) on oxetane in isoSctane and aqueous solutions. Some aspects of possible importance for photochemists working in p-dioxane as... 

Ethylene and formaldehyde are the main products from oxetane (91). Preliminary quantum yield values of some products from p-dioxane (186) and the tetrahydrofurans (188) are presented in Tables 14 and 15. In the case of p-dioxane one is led to propose... 

CF2 CH2 0-CH(CHMe2)-0-CHa] (v) the n.tn,r. spectra of fluorocarbo-hydrates, poiyfluoro-l,4-dioxans, and polyfluoro-l,4-oxathians (vi) vibrational spectra of 3,3-difluoro-oxetan (vii) studies on the cationic copolymerization of 3,3-bis(fluoromethyl)oxetan with THF. ... 

Cyclic ethers can be named in several ways. One simple way is to use teplacement nomenclature, in which we relate the cyclic ether to the corresponding hydrocarbon ring system and use the prefix oxa- to indicate that an oxygen atom replaces a CH2 group. In another system, a cyclic three-membered ether is named oxirane and a four-membered ether is called oxetane. Several simple cyclic ethers also have common names in the examples below, these common names are given in parentheses. Tetrahydrofuran (THF) and 1,4-dioxane are useful solvents ... 

Tiimethylene carbonate is another cychc lactone used to prepare biodegradable polymers.Trimethylene carbonate is prepared either from 1,3-propanediol and ethyl chloroformate or from oxetane and CO2, with the use of an appropriate catalyst. The corresponding polymer, poly(trimeihylene carbonate), is an elastomeric ahphatic polyester with high flexibUity and low mechanical strength. Thus, it is usually copolymerized with GA and dioxane to obtain material for sutures and orthopedic screws. 

Both a-alkoxycyclohexanones and a-alkoxycyclohexenones give oxetans on irradiation. In the former reaction only low yields were obtained, but photolysis of 4-methoxycholest-4-en-3-one in methanol or dioxan gave oxetans (34) and (35) as major products, with smaller amounts of (36), via the initially formed biradical (37). 

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