Oxirane, Oxetane

Oxirane werden in der Regel durch Alkalimetall/Ammoniak, Alkalimetall/Amin oder Alkalimetallamalgam (s.ds. Handb. Bd. VI/3, S. 442) zu Alkoholen gespalten. In ein-zelnen Fallen kann auch Alkalimetall/HMPT herangezogen werden. Es ist jedoch auch Reduktion zu Alkenen moglich. 

Alkyl- und Aikenyl-oxirane werden durch Natrium/Ammoniak in der Weise gespalten, daB sekundare und tcrtiare Alkohole gebildet werden. So entsteht z.B. mit Natrium/fl. Ammoniak aus Methyl- bzw. Athyl-oxiran 2-Propanol6 bzw. 2-Butanol7 (55°/o d.Th.). 

Alken-(l)-yl-oxirane liefern bei der Reduktion mit Alkalimetall/fl. Ammoniak vor-zugsweise die (E)-Allylalkohole, wahrend bei Reduktion mit Diisobutyl-aluminium-hydrid als Hauptprodukt das (Z)-Isomere entsteht8 so erhalt man z.B. aus 

2-Methyl-2-vinyl-oxiran (Li/fl.NHj) 1 -Hydroxy-2-methyl-buien-(2) und 27%d.Th. (10 1) 

3-OCH3 4-OCHj 3 -Methoxy-phenol 8 4-M ethoxy-phenol 92 2 

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Many copolymerization studies have been made. A detailed discussion and critique of the results has been pubHshed (1) and the breadth of the comonomers studied has been summarized (6). Among the comonomers used are oxiranes, oxetanes, 1,3-dioxolane, substituted tetrahydrofurans. 

It is clear from Fig. 8 and Table 1 that the angle 0 does indeed decrease as expected if the n-pair models and rule 1 were applicable. Moreover, the hydrogen bond non-linearity 9 decreases along the series B = oxirane, oxetane, 2,5-dihydrofuran. On the other hand, the values of 9 for oxirane- -ClF and 2,5-dihydrofuran- -ClF (included in Fig. 8) reveal that the halogen bond shows little propensity to be non-linear. 

Cyclic ethers can be named simply as oxacycloalkanes, such as oxacyclopropane, oxacyclo-butane, oxacyclopentane, and oxacyclohexane, where the prefix oxa indicates the replacement of CH2 by O in corresponding cycloalkanes. Most cyclic ethers, however, are known by other names. The 3-, 4-, 5-, and 6-membered rings are oxirane, oxetane, oxolane, and oxane, respectively, or ethylene oxide (or epoxide), trimethylene oxide, tetrahydrofuran, and tetrahydropyran. 

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

Some oxirane, oxetane, and oxolane derivatives of 1,6-anhydrohexoses are known, for example l,6 2,3-dianhydro-/i-D-allofuranose (165) and the corresponding a-L-talofuranose,243 1,6 2,5-dianhydro-a-L-gulofuranose (166),511,512 l,6 3,5-dianhydro-a-L-idofuranose,245 l,6 3,5-dianhydro-a-L-gulofuranose,246,512 and 1,6 4,7-dianhydro-D-g/ycero-/f-D-gulopyranose.249... 

Ring-opening of oxiranes, oxetanes and other cyclic ethers... 

In polymerizations of cyclic ethers with rings smaller than tetrahydrofuran, ring strain affects the position of the equilibria discussed above. Small cycles (oxiranes, oxetanes) cannot be formed from esters with ion pair formation, and the equilibrium is shifted in favour of the macroesters [33, 34],... 

Baldwin and Walker have obtained quantitative experimental data for reaction (9), the kinetically significant reaction (along with reaction (6)) in the formation of oxiranes, oxetanes, tetrahydrofuranes and tetrahydro-pyranes in the generalized sequence. 

Thus, we first discuss thermodynamics, paying attention to features that are important for polymer synthesis (e.g., dependence of equilibrium monomer concentration on polymerization variables) then we describe kinetics and thermodynamics of macrocyclization, trying to combine these two related problems, usually discussed separately. In particular we present the new theory of kinetic enhancement and kinetic reduction in macrocyclics. Thereafter, we describe the polymerization of several groups of monomers, namely cyclic ethers (oxiranes, oxetanes, oxolanes, acetals, and bicyclic compounds) lactones, cyclic sulfides, cyclic amines, lactams, cyclic iminoethers, siloxanes, and cyclic phosphorus-containing compounds, in this order. We attempted to treat the chapters uniformly we discuss practical methods of synthesis of the corresponding polymers (monomer syntheses and polymer properties are added), and conditions of reaching systems state and reasons of deviations. However, for various groups of monomers the quality of the available information differ so much, that this attempt of uniformity can not be fulfilled. 

Cyclic ethers (oxirans, oxetans, tetrahydrofuran) react with HSiEt2Me and CO in the presence of a cobalt catalyst to give silyl-protected hydroxy-aldehydes, a process involving ring opening and carbonyl insertion.Scheme 21 illustrates the... 

C—C Bond Formation. Treatment of an organometaUic intermediate with dry ice and acidification with aqueous HCl affords a carboxylic acid derivative. With paraformaldehyde, one obtains an alcohol, and with oxiranes, oxetanes, and l-iodo-4-(methoxymethoxy)butane, assisted by copper(I) iodide or other Lewis acids, alcohols with different chain lengths are accessible. 

Reactions with Oxiranes, Oxetanes, and Aziridines. Lewis acids, lanthanide salts, and titanium tetraisopropoxide or aluminum isopropoxide catalyze the reactions of cyanotri-methylsilane with oxiranes, oxetanes, and aziridines, yielding ring-opened products. The nature of the products and the regio-selectivity of the reaction are primarily dependent on the nature of the Lewis acid, the substitution pattern in the substrate, and the reaction conditions. Monosubstituted oxiranes undergo regiospe-cific cleavage to form 3-(trimethylsiloxy)nitriles when refluxed with a slight excess of cyanotrimethylsilane in the presence of a catalytic amount of potassium cyanide-18-crown-6 complex (eqs 8-10). The addition of cyanide occurs exclusively at the least-substituted carbon. 

The S5mthesis of l,3-dioxolan-2-ones and related l,3-dioxan-2-ones, also known as five- and six-membered cyclic carbonates, has a rich history and the earliest report dates back to the 1950s [45]. The most common method to produce cyclic carbonates (which has also been commercialized) is the coupling reaction between oxiranes/oxetanes... 

In the lUPAC nomenclature system, the names for cyclic ethers with three-, four-, five-, and stx-mem-bered rings are oxirane, oxetane, oxolane, and oxane, respectively. The oxygen atom in each of these rings receives the number 1 in both common names and lUPAC nomenclature. The ring is numbered in the direction that gives the lowest number to the first substituent. 

The appearance of sulfonium salts as end groups in polymers produced using these photoinitiators supports this conclusion Among those monomers which undergo facile polymerization with dialkylphenacylsulfonium and dialkyl-4-hydroxyphenyl-sulfonium salts include oxiranes, oxetanes, thiiranes, vinyl ethers and s-trioxane. Polymerizations of tetrahydrofuran, e-caprolactone, a-methylstyrene, and N-vinyl-2-pyrrolidone are very sluggish and often fail using these photoinitiators. 

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