2.3- Epoxy halides

Optically active allylic alcohols and homoallylic epoxides. The reaction of optically active 2,3-epoxy halides (1), available by Sharpless asymmetric epoxidation of allylic alcohols, with a preformed mixture of vinylmagncsium bromide and Cul (2 equiv. each) in THF at —23° does not result as expected (7.H1-82) in a homoallylic epoxide, but... 

The reaction courses of 2,3-epoxy halides depend on structures and reaction conditions. When C-3 is substituted with an aryl group and the reduction is carried out in THF-HMPA, 2-arylcyclopropanols are produced. Otherwise the products are the allylic alcohols. 

As expected on the basis of the epoxy halide results just discussed, die displacement of a primary tosyl-ate can be smoothly accomplished in the presence of an adjacent disubstituted epoxide,and this reaction has been utilized in syntheses of disparlure and of other insect pheromones. On the other hand, a recently reported reaction of a cyclic glucopyranose-derived epoxide with either Me2CuLi or MeMgCl-CuBr afforded in high yield the desired ring-opened product, leaving intact an exocyclic primary mesylate. 

Cleavage of 2,3-epoxy halidesA zinc-copper couple, prepared by sonication of zinc powder and Cui in aqueous ethanol, cleaves epoxy halides to a radical that rearranges to an allylic alcohol. Since the epoxy halide is prepared by epoxidation of an allylic alcohol (m-chloroperbenzoic acid) followed by reaction with P(ChH5)3 and CBr4, the reaction effects 1,3-transposition of the hydroxyl group. 

Bromocresol purple (5.2...6.8) glutamic and ketoglutaric acids [217], halide and halate anions [91,218, 219] preservatives [220, 221] products of pyrolysis of epoxy resins [222] 5-aminodibenzocyclo-heptane derivatives [223] phenylalkanolamines, eph-edrine [224]... 

Grignard reagents are powerful nucleophiles => it is not possible to prepare a Grignard reagent from any organic halide that contains a carbonyl, epoxy, nitro, or cyano group. 

Elemental Analyses. X-ray fluorescence measurements of the molded epoxy discs are summarized in Table II. Halide concentrations were determined by aqueous extraction and are presented in Table III. 

Elemental Analyses. X-ray fluorescence measurements (Table II) indicate no major difference between the total Br content in the FR silicone-epoxy (sample A). However, extractable halide concentrations, listed in Table III, are much lower for the silicone-epoxy samples. 

Analytically, epoxy groups are determined by the reaction with hydrogen halide and back titration with a standard base. Other functional groups present may cause interference problems and result in poor end points. Pyridinium chloride-pyridine is a recommended reagent for the analysis of bisphenol-diglycidyl ether resins [22,23],... 

For detection and quantitative determination of small quantities of epoxy groups, these groups may be reacted with dinitroarene sulfonic acids [7,20,21,24], which react nearly as rapidly as hydrogen halides. 

Related to the epoxy ether preparations is another reaction, involving the same precursors and an essentially identical mechanism. When certain a-haloketones are treated -with potassium cyanide in aqueous alcoholic media, there are obtained, among other products, glycidonitriles. In this instance the carbonyl function suffers attack by a CN ion, rather than a methoxide, and the intermediate an kin collapses quickly to a glytddonitrile by ejecting a halide ion as shown in Eq. (228). 

Other monoalkylated ethylene oxides reported to undergo ready cleavage on treatment with halogen adds (Eq. 701) include 1,2-epoxy-butane,1 1,2-epoxyhexane,1 00 and 1,2-epoxyheptane. 41 Although the last two have been said to yield only secondary alcohols, corresponding to exclusive attack of halide on the terminal epoxide carbon atom, it ie probable that isomeric alcohols are also formed in small undetected quantities... 

A modest assortment of storoidal e -epoxy ketones (EqB. 737-740) have been subjected to the action of hydrogen halides, among them... 

Primary allylic halides may be efficiently asymmetrically dihydroxylated in 40-98% ee. The products may be readily converted into epoxy alcohols in high yields, by treatment with NaOH in THF (equation 19)116. 

Epoxy-1-propanols are preferentially attacked by halides at C-3. This regio-selectivity can be enhanced further by acidic reaction conditions or by addition of Ti(IV) salts. Attack at C-2 is promoted by boron-derived Lewis acids (fourth reaction, Scheme 4.91). 

Ring opening of epoxides by halides is reversible, and from 2,3-epoxy-l-propanols primary halides can be obtained by a sequence of epoxide openings and epoxide formations (last reaction, Scheme 4.91). 

C-l Reactivity of 2,3-epoxy alcohols via oxirane opening with metal halides applications and synthesis of naturally occurring 2,3-octanediol,... 

This Cu species on reaction with epoxyalkyl halides forms an epoxyalkylcopper reagent. This undergoes an intramolecular cyclization via epoxy cleavage. The regioselectivity of reaction of Cu with the substrate 1 can be controlled by the... 

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