Epoxides isolation

Peroxyl radicals are well-known in chemical systems to epoxidize isolated double bonds such as the 9,10-double bond of BP-7,8-dihydrodiol (Equation 6) ( 7 ). However, they have been largely ignored as... 

Recently, Indian workers (61) reported that 2-naphthylmethylene triphenylarsorane reacted with substituted benzaldehydes to give the corresponding epoxides exclusively, whereas l-bromo-2-naphthylmethylene triphenylarsorane reacted with substituted benzaldehydes to give only olefins. In no case were both olefin and epoxide isolated and in all cases only fram-epoxides or trans-olefins were detected. It has also been reported that reaction of indole-3-carboxaldehyde with semistabilized ar-sonium ylides followed only the trans -carbonyl olefination (91). 

Nitrobenzenesulfonyl peroxy (A) or sulfinylperoxy (B) intermediates (Figure 6), generated at low temperature from 2-nitrobenzenesulfonyl- or -sulfinyl chloride with K02, serve as excellent oxidizing agents and preferentially epoxidize isolated double bonds rather than enones [Pg.138]

Amphidinolide A is a 20-memhered macrolide possessing a dienoate chromophore, three aro-methylenes, two 1,2-diols, three branched methyl groups, and an epoxide, isolated from Amphidinium sp. (strain Y-5), which was separated from the marine acoel flatworm Amphiscolops sp. collected off Chatan heach, Okinawa. Originally, the stereochemistries of nine chiral centers in amphidinolide A (1) were proposed to he (32) on the basis of nuclear Overhauser enhancement and exchange spectroscopy (NOESY) correlations and y values. However, the total synthesis of... 

Amphidinolide V (21) is a 14-membered macrolide possessing four dxo-methylenes and an epoxide, isolated from the marine dinoflagellate Amphidinium sp. (strain Y-5). The relative stereochemistry of amphidinolide V was deduced from the combination of the molecular mechanics calculation and the analyses of H- H coupling constants and NOESY data. Recently, a total synthesis of the proposed structure of amphidinolide V (21) has been achieved by Fiirstner group (Scheme 6). Comparison of the NMR data and CD spectrum of the... 

Very recently physagulin C epoxide) isolated by Shingu et al. from Physalis angulata L. 

Pace-Asciak CR, Granstr5m E, Samuelsson B. Arachidonic acid epoxides. Isolation and structure of two hydroxyepoxide intermediates in the formation of 8,11,12 and 10,11,12-trihydroxy-eicosatrienoic acids. J Biol Chem 1983 258 6835-6840. 

Perhaps this scheme might be extended to 5,6-epoxides (isolated from Anthe-mideae species) (Bohlmann, Arndt, Bornowski, Jastrow and Kleine, 1962) to account for the Anthemideae spiroketals with a five and a six membered ring. [See also addendum ]. 

Kigoshi, H., Ojika, M., Shizuri, Y, Niwa, H., and Yamada, K. (1982) (10R,llR)-(+)-squalene-10,11-epoxide isolation from Laurencia okamurai and the asymmetric synthesis. Tetrahedron Lett., 23, 5413-5414. 

The 9 — 15 fragment was prepared by a similar route. Once again Sharpless kinetic resolution method was applied, but in the opposite sense, i.e., at 29% conversion a mixture of the racemic olefin educt with the virtually pure epoxide stereoisomer was obtained. On acid-catalysed epoxide opening and lactonization the stereocentre C-12 was inverted, and the pure dihydroxy lactone was isolated. This was methylated, protected as the acetonide, reduced to the lactol, protected by Wittig olefination and silylation, and finally ozonolysed to give the desired aldehyde. 

A single epoxide was isolated in 79-84% yield in the following reaction Was this epoxide A or B" Explain your reasoning... 

The zwitterion (6) can react with protic solvents to produce a variety of products. Reaction with water yields a transient hydroperoxy alcohol (10) that can dehydrate to a carboxyUc acid or spHt out H2O2 to form a carbonyl compound (aldehyde or ketone, R2CO). In alcohoHc media, the product is an isolable hydroperoxy ether (11) that can be hydrolyzed or reduced (with (CH O) or (CH2)2S) to a carbonyl compound. Reductive amination of (11) over Raney nickel produces amides and amines (64). Reaction of the zwitterion with a carboxyUc acid to form a hydroperoxy ester (12) is commercially important because it can be oxidized to other acids, RCOOH and R COOH. Reaction of zwitterion with HCN produces a-hydroxy nitriles that can be hydrolyzed to a-hydroxy carboxyUc acids. Carboxylates are obtained with H2O2/OH (65). The zwitterion can be reduced during the course of the reaction by tetracyanoethylene to produce its epoxide (66). 

Arsenic Peroxides. Arsenic peroxides have not been isolated however, elemental arsenic, and a great variety of arsenic compounds, have been found to be effective catalysts ia the epoxidation of olefins by aqueous hydrogen peroxide. Transient peroxoarsenic compounds are beheved to be iavolved ia these systems. Compounds that act as effective epoxidation catalysts iaclude arsenic trioxide, arsenic pentoxide, arsenious acid, arsenic acid, arsenic trichloride, arsenic oxychloride, triphenyl arsiae, phenylarsonic acid, and the arsenates of sodium, ammonium, and bismuth (56). To avoid having to dispose of the toxic residues of these reactions, the arsenic can be immobi1i2ed on a polystyrene resia (57). 

Garyophyllene. (-)-CaryophyUene can be isolated from Indian turpentine and has been used to prepare a number of woody aroma products. The epoxides are produced by reaction with peracids. Acetylation of caryophyUene also gives a usehil methyl ketone (180) (Fig. 8). Acid-catalyzed rearrangement of caryophyUene in the presence of acetic acid gives a mixture of esters, which are related to caryolan-l-ol and clovan-2-ol (181). 

The double bonds of avermectins react with y -chloroperbenzoic acid to give 3,4-, 8,9-, and 14,15-epoxides. The 8,9-epoxide is the primary product and can be isolated in good yield (45). The 8,9-epoxide was opened by aqueous acids to the 8,9-diol (46). The 3,4-diol can be obtained readily and regiospecificaHy by osmium tetroxide oxidation. Neither peracids nor OsO will attack the 22,23-double bond. 

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). 

Caution The. yield isolated from this reaction depends on the efficiency of this condenser the epoxidation is exothermic and methylenecyclopropane is volatile. 

This remarkably selective internal epoxidation of peroxyarachidonic acid to form 14,15-oxido-arachidonic acid occurs as shown because of unusually favorable stereoelectronics. The corresponding reaction sequence with eicosa-(E)-8,ll,14-trienoic acid affords the Ai4,i5 epoxide in 94% isolated yield and >95% purity. 

Many selective epoxidations are possible with polyunsaturated steroids. In general, oc, -unsaturated ketones are not attacked by peracid, although linear dienones react slowly at the y,5-double bond. Aw-Chloroperbenzoic acid is the reagent of choice for this reaction.When two isolated double bonds are present in the steroid nucleus, e.g. (27) and (30), the most highly substituted double bond reacts preferentially with the peracid. Selective epoxidation of the nuclear double bond of stigmasterol can likewise be achieved.However, one exception to this general rule has been reported [See (33) (34)]. ... 

Anomalous results in the peracid reaction are usually encountered when the resulting epoxides are particularly sensitive to acid. For this reason A - and A -steroid epoxides are difficult to isolate. The rearrangements... 

Hydrolysis of the intermediate epoxy acetate is generally carried out with strong alkali if base-sensitive groups are present, milder conditions (e.g., potassium bicarbonate, potassium carbonate) can be employed. If commercial peracetic acid (which contains sulfuric acid) is used for epoxidation, the intermediate epoxy acetate cannot be isolated, but is hydrolyzed in situ by the acid to the desired ketol. Acid hydrolysis will also retain 3-acetates, if present. ... 

In a typical Knof procedure, 3jS-hydroxyandrost-5-en-17-one acetate is epoxidized with perbenzoic acid (or m-chloroperbenzoic acid ) to a mixture of 5a,6a- and 5)5,6)5-epoxides (75) in 99 % yield. Subsequent oxidation with aqueous chromium trioxide in methyl ethyl ketone affords the 5a-hydroxy-6-ketone (76) in 89% yield. Baeyer-Villiger oxidation of the hydroxy ketone (76) with perbenzoic acid (or w-chloroperbenzoic acid ) gives keto acid (77) in 96% yield as a complex with benzoic acid. The benzoic acid can be removed by sublimation or, more conveniently, by treating the complex with benzoyl chloride and pyridine to give the easily isolated )5-lactone (70) in 40% yield. As described in section III-A, pyrolysis of j5-lactone (70) affords A -B-norsteroid (71). Knof used this reaction sequence to prepare 3)5-hydroxy-B-norandrost-5-en-17-one acetate, B-noran-... 

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]... 

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