Other Oxirane Syntheses

A similar principle is observed in the reaction of seleno-anions 88 with ketones and aldehydes Eq. 

The chemoselective synthesis of alkenyloxiranes can be achieved from a,j3-unsatura-ted ketones.  

If the carbanionic carbon atom in a-halolithium compounds is reacted with carbonyl compounds, a C-C bond is created this provides a convenient, general oxirane synthesis (Eq. 

Bisoxiranes can be prepared from dioxo compounds. With geminal chloromethyl-allyllithium the synthesis of new a-vinyl tri- and tetrasubstituted oxiranes has been developed (Eq. 93).  

Reaction of bis-(trimethylsilyl)bromomethyllithium with benzophenone gives the corresponding oxirane derivative.  

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N-alkylated (e.g., A-methyl and A-ethyl) perfluoroalkanesulfonamides can be converted into nonionic surfactants with a polyoxyethylene head group by reaction of the sulfonamide with excess oxirane in the presence of a base. This synthesis approach is similar to the one outlined in Section 18.2.3.2 for the synthesis of perfluoroalkanesulfonamidoethanols. The reaction of A-methylperfluorobutanesulfonamide with oxirane yields the desired polyoxyethylene surfactants in the presence of potassium hydroxide at 100-120°C (Scheme 18.7). A different approach to similar polyoxyethylene surfactants claims the reaction of perfluoroalkanesulfonamidoethanols with oxirane in the presence of sodium hydroxide as a catalyst (Scheme 18.7). Both approaches can also be extended to other oxirane derivatives, or use perfluoroalkanesulfonamides such as the ones shown in Scheme 18.3 as starting materials. " Polyoxyethylene groups can also be attached to... 

The derivatives are hydroxyethyl and hydroxypropyl cellulose. AH four derivatives find numerous appHcations and there are other reactants that can be added to ceUulose, including the mixed addition of reactants lea ding to adducts of commercial significance. In the commercial production of mixed ethers there are economic factors to consider that include the efficiency of adduct additions (ca 40%), waste product disposal, and the method of product recovery and drying on a commercial scale. The products produced by equation 2 require heat and produce NaCl, a corrosive by-product, with each mole of adduct added. These products are produced by a paste process and require corrosion-resistant production units. The oxirane additions (eq. 3) are exothermic, and with the explosive nature of the oxiranes, require a dispersion diluent in their synthesis (see Cellulose ethers). 

This chapter will deal exclusively with three-membered rings containing the hetero atoms O, S and N, and fused to the steroid skeleton. Because of the conformational requirements in steroids, not all of the usual methods of synthesis of three-membered rings are applicable to the fused ring system. For the synthesis of steroids to which an aziridine, oxirane or thiirane is attached either in the side chain or at a ring position but not directly fused to the nucleus, the methods discussed in this chapter, as well as others, are applicable. 

Epoxyfarnesol was first prepared by van Tamelen, Stomi, Hessler, and Schwartz 4 using essentially this procedure. It is based on the findings of van Tamelen and Curphey5 that N-bromosuccinimide in a polar solvent was a considerably more selective oxidant than others they tried. This method has been applied to produce terminally epoxidized mono-, sesqui-, di-, and triterpene systems for biosynthetic studies and bioorganic synthesis.6 It has also been applied successfully in a simple synthesis of tritium-labeled squalene [2,6,10,14,18,22-Tetracosahexaene, 2,6,10,15,19,23-hexamethyl-, (all-E)-] and squalene-2,3-oxide [Oxirane, 2,2-dimethyl-3-(3,7,12,16,20-pentamethyl-3,7,ll,-15,19-heneicosapentaenyl)-, (all-E)-],7 and in the synthesis of Cecropia juvenile hormone.8... 

The use of other phosphorus-sulfur reagents for heterocyclic synthesis appears rare. It would be interesting to investigate in more detail the reaction of compounds, such as the phosphine sulfides, with organic substrates. Triphenylphosphine sulfide is an effective sulfur transfer agent, as it converts oxiranes into thiiranes in good yield. The reaction proceeds with retention of configuration.128... 

The reaction occurs quickly at low temperature, with inversion of configuration at the attacked carbon center. The oxirane is reacting usually at the less hindered site. This reaction has found widespread use in organic synthesis , particularly in the case of stabilized organolithium and alkynyllithium species (see Section IV.B.2). In the intramolecular versions, the presence of BF3 has been reported to modify the regioselectivity". Other Lewis acids such as organolanthanids or LiC104 have also been used to a lesser extent. 

So far, no reference has been made to the presence of more than one phase in the reactor. Many important chemicals are manufactured by processes in which gases react on the surface of solid catalysts. Examples include ammonia synthesis, the oxidation of sulphur dioxide to sulphur trioxide, the oxidation of naphthalene to phthalic anhydride and the manufacture of methanol from carbon monoxide and hydrogen. These reactions, and many others, are carried out in tubular reactors containing a fixed bed of catalyst which may be either a single deep bed or a number of parallel tubes packed with catalyst pellets. The latter arrangement is used, for exjimple, in the oxidation of ethene to oxiran (ethylene oxide)... 

Bromotrimethylsilane has proven to be useful for a wide variety of applications most of them being reviewed.5 8 Other recent applications are mild cleavage of oxiranes,9 the synthesis of glycosyl bromides,10 the selective cleavage of tetrahydro-2,5-dimethoxyfuran and tetrahydro-2,6-dimethoxy-pyran,11 the cleavage of esters and ethers,12 and the synthesis of benzyl bromides.13... 

Tetr 39 2323 (1983) (Recent Advances in the Preparation and Synthetic Applications of Oxiranes) 43 3309 (1987) (Synthetic Routes to Tetrahydrofuran, Tetrahydropyran, and Spiroketal Units of Polyether Antibiodcs and a Survey of Spiroketals of Other Natural Products) SO 8885 (1994) (Chemical and Biological Synthesis of Chiral Epoxides)... 

Epoxy sugars are frequently used as starting compounds in the synthesis of sugar derivatives (compare Section IV) such as halo, amino, azido, thio, deoxy, and branched-chain derivatives. The oxirane ring is in general more reactive than the oxetane or oxolane ring. It is opened with nucleophiles under base or acid catalysis. On the other hand, the oxirane ring remains unattacked under the conditions of catalytic debenzylation on palladium,... 

With the purpose of increasing the range of available block copolymers, comonomers other than methacrylates and acrylates can also be involved in sequential polymerization, provided that they are susceptible to anionic polymerization. Dienes, styrene derivatives, vinylpyridines , oxiranes and cyclosiloxanes are examples of such comonomers. The order of the sequential addition is, however, of critical importance for the synthesis to be successful. Indeed, the pX a of the conjugated acid of the living chain-end of the first block must be at least equal to or even larger than that of the second monomer. Translated to a nucleophilicity scale, this pK effect results in the following order of reactivity dienes styrenes > vinylpyridines > methacrylates and acrylates > oxiranes > siloxanes. 

Epoxide formation using biocatalysis is a useful process for the formation of chiral oxiranes (Scheme 29). The synthesis of enantioenriched epoxides using enzymes has been reviewed <1995BCSF769>. Chloroperoxidase has been examined for the oxidation of 2-methyl-l-alkenes, among other alkenes. The yields in some cases can be low, but the enantioselectivities can be high <1995JA6412, 1997JA443>. This enzyme has been used in a synthesis of... 

A polyadduct formed from aniline, phenothiazine, oxirane and 2,3-epoxypropane [145] was proposed as a component for the synthesis of a light stable PUR. A polyadduct of 4,4 -isopropylidenebisphenol with 2-hydroxy-4-(2,3-epoxypropyl)-benzophenone [131], polymeric HALS 115 formed from bis(2,3-epoxypropyl)ani-line and 4-amino-2,2,6,6-tetramethylpiperidine [146] or a brominated oligomer 116 used in combination with antimony trioxide as FR for PET [147] are other examples of polyaddition stabilizers. 

Conventional texts on organic chemistry are usually divided into chapters corresponding to compound types, chemical reactions, synthetic methods, etc. From the viewpoint of synthesis, this traditional classification should be supplemented by consideration of the specific aspects of synthetic relationships i.e. into what a given compound can be converted and from what it can be obtained, in other words, its place in the solution of synthetic tasks. For example, in accordance with conventional classification, alkenes, alkynes, cyclopropanes, and oxiranes fall into substantially different and rather distant taxons of organic chemistry systematics. These classes traditionally are treated as independent and only remotely related areas of organic chemistry. However,... 

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