Oxiranes substituted

Hydroxyethyl cellulose, three samples prepared from alkali cellulose and ethylene oxide (oxirane) to low degrees of molar substitution (MS) about 0.25, 0.4 and 0.6 moles of oxirane substituted per mole of glucose units (some oxirane units form substituted oligo-ethylene glycol chains). 

The polymerization of cyclic ethers like oxirane substituted oxiranes and bicyclic tetrahydrofurans proceeds with inversion of configuration on the carbon atom, stron y suggesting the 8 2 mechanism. 

In the oxides of styrene, stilbene, and stilbazole, the chemical shifts of the cis protons of the oxirane ring are larger than those for the trans isomers. This can be explained by the polarization effect of the electric dipole moment of one of the CH protons on the other CH. The anisotropc shielding of the ring in the case of oxiranes substituted with an aromatic group can be utilized well in the determination of the configuration. ... 

Oxiranes substituted with acetal groups ZnEt2/MeOH, ZnEt2/cyclohexanol 78... 

Oxiranes substituted with ester groups AIEt3/H20/acetylacetone 85... 

Oxiranes substituted with organosilane or organosiloxane ZnEta/HaO 86... 

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

In stereoselective antitheses of chiral open-chain molecules transformations into cyclic precursors should be tried. The erythro-configurated acetylenic alcohol given below, for example, is disconnected into an acetylene monoanion and a symmetrical oxirane (M. A. Adams, 1979). Since nucleophilic substitution occurs with inversion of configuration this oxirane must be trens-conilgurated its precursor is commercially available trans-2-butene. 

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. 

With appropriately substituted oxetanes, aluminum-based initiators (321) impose a degree of microstmctural control on the substituted polyoxetane stmcture that is not obtainable with a pure cationic system. A polymer having largely the stmcture of poly(3-hydroxyoxetane) has been obtained from an anionic rearrangement polymerisation of glycidol or its trimethylsilyl ether, both oxirane monomers (322). Polymerisation-induced epitaxy can produce ultrathin films of highly oriented POX molecules on, for instance, graphite (323). Theoretical studies on the cationic polymerisation mechanism of oxetanes have been made (324—326). 

Some examples of ring opening reactions with carbanions leading to five-membered heterocyclic ring formation are shown in Scheme 85. Pyrrole syntheses from functionally substituted oxiranes and amines are often described and typical examples are shown in Scheme 86. 

These are discussed in (B-71MS4). Oxirane itself shows a strong molecular ion peak and a slightly stronger base peak at mje 29 (CHO ) due to isomerization to ethanal and loss of a methyl radical. Substituted oxiranes tend to show only weak molecular ion peaks, because of rearrangement and fragmentation. 

Oxirane on thermolysis or photolysis suffers C—O homolysis to give a plethora of products (Scheme 2). Substituted oxiranes behave similarly on thermolysis although some C—C cleavage is observed (Scheme 3). Cyclopentene and cyclohexene oxides undergo only C—O cleavage (Scheme 4). 

Table 3 Favored Position of Nucleophilic Attack on Substituted Oxiranes ...

Alkyl groups under nonacidic conditions sterically deflect nucleophiles from C, but under acidic conditions this steric effect is to some extent offset by an electronic one the protonated oxirane opens by transition states (Scheme 40) which are even more 5Nl-like than the borderline Sn2 one of the unprotonated oxirane. Thus electronic factors favor cleavage at the more substituted carbon, which can better support a partial positive charge the steric factor is still operative, however, and even under acidic conditions the major product usually results from Cp attack. 

The oxaziridine ring itself is stable towards alkali there is, for instance, no substitutive ring opening by hydroxyl ions as in oxiranes. 2-r-Butyl-3-phenyloxaziridine (56) is not attacked by methoxide ion in methanol during 12 h at room temperature 3-isopropyl-2-r-octyloxaziridine does not react at room temperature with either solid potassium hydroxide or potassium methoxide solution (57JA5739). 

The effect of an a-substituted oxirane group on the optical rotatory dispersion of steroidal ketones should be interpreted with caution an inverted octant rule for a-epoxy ketones has been proposed/although recent data indicate that the normal octant rule may still be valid. 

The combination of alkali metal acid fluorides and porous aluminum fluoride IS a stable, solid, and efficient substitute for anhydrous hydrogen fluoride for promoting the ring-opening reactions of simple aliphatic oxiranes to give the fluorohydrins under sonication [/5] (equations 14 and 15)... 

Polyfluoroalkyl- andperfluoroalkyl-substituted CO and CN multiple bonds as dipolarophiles. Dmzo alkanes are well known to react with carbonyl compounds, usually under very mild conditions, to give oxiranes and ketones The reaction has been interpreted as a nucleophilic attack of the diazo alkane on the carbonyl group to yield diazonium betaines or 1,2,3 oxadiazol 2 ines as reaction intermediates, which generally are too unstable to be isolated Aromatic diazo compounds react readily with partially fluorinated and perfluorinated ketones to give l,3,4-oxadiazol-3-ines m high yield At 25 °C and above, the aryloxa-diazolines lose nitrogen to give epoxides [111]... 

Epoxides are normally nmned as epoxy derivatives of alkanes or as substituted oxiranes. 

In a scheme intended to produce a more highly substituted oxazolidone, epichlorohydrin is condensed with morpholine in the presence of strong base to give the aminoepoxide, 27. Ring opening of the oxirane by means of hydrazine gives the hydroxy-hydrazine (28). Ring closure with diethyl carbonate leads to the substituted oxazolidone (29). Condensation with 18 affords furaltadone (30). ... 

Substitution of an additional nitrogen atom onto the three-carbon side chain also serves to suppress tranquilizing activity at the expense of antispasmodic activity. Reaction of phenothia zine with epichlorohydrin by means of sodium hydride gives the epoxide 121. It should be noted that, even if initial attack in this reaction is on the epoxide, the alkoxide ion that would result from this nucleophilic addition can readily displace the adjacent chlorine to give the observed product. Opening of the oxirane with dimethylamine proceeds at the terminal position to afford the amino alcohol, 122. The amino alcohol is then converted to the halide (123). A displacement reaction with dimethylamine gives aminopromazine (124). ... 

A comparison of the configuration of the substrates and reaction products shows that the oxiranyl anions arc configurationally stable under the reaction conditions. Only one example is known in which isomerization was observed. When the ci.v-tm-butyl-substituted epoxysilane27 was metalated and quenched with 2-cyclohexenone, addition product 27 was obtained under inversion of the anionic center. Presumably the strain created in forcing the ter/-butyl and the trimethylsilyl group cis on the oxirane ring facilitates the isomerization process13. 

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