Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Of oxiranes

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.). [Pg.50]

Uses. Magnesium iodide is used in the deoxygenation of oxiranes into olefins and iodine. This step is important to organic chemistry because it helps in the stmcture elucidation of complex organic molecules (110). Eor example. [Pg.351]

The parallel ability of oxiranes to undergo ring opening to carbonyl ylides was first noted in the case of tetracyanooxirane (68T2551), but such reactions have not been widely exploited. The addition to alkenes, leading to formation of tetrahydrofurans, is stereospecific (Scheme... [Pg.138]

B-81MI50500) A general review of oxiranes deals mainly with 1965-1977. [Pg.97]

The geometries of oxiranes have been determined mainly by X-ray diffraction on crystalline natural products, the oxirane ring being widespread in nature (Section 5.05.5.3). However, the detailed structure of the parent compound (Figure 1) has been secured by microwave spectroscopy and electron diffraction studies (64HC(l9-l)l). The strain in this... [Pg.97]

The gas phase thermal chemistry and photochemistry of oxiranes is reviewed in (77CRV473). References to thermal reactions of oxiranes are given in (B-80MI50502) and ref. 10 in (76TL1449). [Pg.100]

The reaction of oxiranes with base can follow several paths, giving products of type (34-38 Scheme 27). (a) Formation of an oxiranyl anion (34) is rare (Section 5.05.3.5). (b) Nucleophilic ring opening to give (35) is common with unhindered bases (Section 5.05.3.4). (c) a-Elimination to give a carbene or carbenoid (36) is favored by alkyllithium bases and... [Pg.103]

Molecular orbital calculations predict that oxirane forms the cyclic conjugate acid (39), which is 30 kJ moF stabler than the open carbocation (40) and must surmount a barrier of 105kJmoF to isomerize to (40) (78MI50500). The proton affinity of oxirane was calculated (78JA1398) to be 807 kJ mol (cf. the experimental values of 773 kJ moF for oxirane and 777-823 kJ moF for dimethyl ether (80MI50503)). The basicity of cyclic ethers is discussed in (B-67MI50504). [Pg.105]

A relatively few oxirane ring openings have been reported to give retention or a mixture of inversion and retention (see the general reviews on the mechanisms of oxirane ring opening, and the specialized one devoted to retention (68RCR448)). [Pg.110]

Nucleophilic opening of oxiranes to give ultimately 1,2-diols is usually effected without isolation of the oxirane oxiranation (epoxidation) of alkenes with unbuffered peroxy-ethanoic acid or hydrogen peroxide in methanoic acid (Section 5.05.4.2.2(/)) tends to give monoesters of 1,2-diols (e.g. 53), which can be hydrolyzed to the diols (Scheme 46). [Pg.110]

Reductive cleavage of oxiranes to alcohols by lithium aluminum hydride is an important reaction (64HC(19-1)199), but the most powerful hydride donor for this purpose is lithium triethylborohydride (73JA8486). [Pg.112]

The most important oxirane syntheses are by addition of an oxygen atom to a carbon-carbon double bond, i.e. by the epoxidation of alkenes, and these are considered in Section 5.05.4.2.2. The closing, by nucleophilic attack of oxygen on carbon, of an OCCX moiety is dealt with in Section 5.05.4.2.1 (this approach often uses alkenes as starting materials). Finally, oxirane synthesis from heterocycles is considered in Section 5.05.4.3 one of these methods, thermal rearrangement of 1,4-peroxides (Section 5.05.4.3.2), has assumed some importance in recent years. The synthesis of oxiranes is reviewed in (B-73MI50500) and (64HC(19-1U). [Pg.114]

Other syntheses of oxiranes which are occasionally useful and involve a species (64) are the dehydration of 1,2-diols (Scheme 69) (78TL5153, 7808(58)12) and the reductive coupling of aldehydes (Scheme 70) (B-73MI50500). [Pg.115]


See other pages where Of oxiranes is mentioned: [Pg.11]    [Pg.208]    [Pg.210]    [Pg.41]    [Pg.45]    [Pg.97]    [Pg.97]    [Pg.97]    [Pg.97]    [Pg.98]    [Pg.98]    [Pg.99]    [Pg.99]    [Pg.100]    [Pg.100]    [Pg.111]    [Pg.112]    [Pg.113]   
See also in sourсe #XX -- [ Pg.299 ]

See also in sourсe #XX -- [ Pg.583 , Pg.586 ]




SEARCH



Addition of halogen fluondes oxiranes

Anionic Polymerization of Oxiranes and Thiiranes

Anionic polymerization of oxiranes

Block Copolymerisation of Oxiranes and

Cationic Oligomerization of Oxiranes Leading to Linear Oligomers Activated Monomer Mechanism

Cationic polymerization of oxiranes

Cleavage of oxiranes

Coordination polymerization of oxiranes

Copolymerisation of Oxiranes and Carbon

Copolymerisation of Oxiranes and Cyclic Acid

Eliminations of oxiranes

Energy of the Oxirane Ring

Hydrogenolysis of Oxiranes

Nucleophilic ring opening, of oxiranes

Of oxiranes and thiiranes

Oxidation of Epoxides (Oxiranes)

Oxirane Oligomer of Resorcinol—Plastonics International

Oxirane derivatives, of aldoses

Oxiranes use of boron trifluoride

Photochemistry of oxirans

Physical Properties of Oxiranes

Polymerization of oxirane

Polymerization, of oxiranes

Preparation of Oxiranes

Reaction of Lithiomethyl Isocyanide with Hexyl Bromide, Oxirane and Cyclohexanone

Reaction of alkene oxides (oxiranes) with sulfur compounds

Reactions of Oxiranes

Reactivity of Oxiranes

Rearrangement, of: (cont oxiranes

Rearrangements of oxiranes

Reduction, of oxiranes

Regioselectivity of oxiranes

Ring Transformation of Oxiranes into other Heterocyclic Compounds

Ring opening of oxiranes

Ring opening of oxirans

Ring opening polymerization of oxiranes

Ring-Opening Reactions of Oxiranes

Ring-opening of oxiranes, oxetanes and other cyclic ethers

Ring-opening reactions of oxirane

Steric control in polymerization of oxiranes

Sulfoxide, dimethyl oxiranation of carbonyl compounds

Synthesis of Chiral Oxirans

Synthesis of Oxiranes

Tables of Aldose Oxiranes

Williams, Neil R., Oxirane Derivatives of Aldoses

© 2024 chempedia.info