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Epoxides sodium borohydride

In the reaction between peroxymercurials and sodium borohydride, epoxide formation and deoxymercuration compete with hydrogenodemercuration (Scheme 30). Except for the synthesis of t-butyl... [Pg.854]

In analogy with the peracid attack on steroidal double bonds, the formation of the bromonium ion, e.g., (81a), occurs from the less hindered side (usually the a-side of the steroid nucleus) to give in the case of the olefin (81) the 9a-bromo-l l -ol (82). Base treatment of (82) provides the 9 5,1 l S-oxide (83). Similarly, reaction of 17/3-hydroxyestr-5(10)-en-3-one (9) with A -bromosuccinimide-perchloric acid followed by treatment with sodium hydroxide and sodium borohydride furnishes the 3, 17 5-dihydroxy-5a,l0a-oxirane. As mentioned previously, epoxidation of (9) with MPA gives the 5, 10 -oxirane. °... [Pg.17]

The azidohydrins obtained by azide ion opening of epoxides, except for those possessing a tertiary hydroxy group, can be readily converted to azido mesylates on treatment with pyridine/methanesulfonyl chloride. Reduction and subsequent aziridine formation results upon reaction with hydrazine/ Raney nickel, lithium aluminum hydride, or sodium borohydride/cobalt(II)... [Pg.27]

Alkylation of enamines with epoxides or acetoxybromoalkanes provided intermediates for cyclic enol ethers (668) and branched chain sugars were obtained by enamine alkylation (669). Sodium enolates of vinylogous amides underwent carbon and nitrogen methylation (570), while vicinal endiamines formed bis-quaternary amonium salts (647). Reactions of enamines with a cyclopropenyl cation gave alkylated imonium products (57/), and 2-benzylidene-3-methylbenzothiazoline was shown to undergo enamine alkylation and acylation (572). A cyclic enamine was alkylated with methylbromoacetate and the product reduced with sodium borohydride to the key intermediate in a synthesis of the quebrachamine skeleton (57i). [Pg.357]

The synthesis of key intermediate 12, in optically active form, commences with the resolution of racemic trans-2,3-epoxybutyric acid (27), a substance readily obtained by epoxidation of crotonic acid (26) (see Scheme 5). Treatment of racemic 27 with enantio-merically pure (S)-(-)-1 -a-napthylethylamine affords a 1 1 mixture of diastereomeric ammonium salts which can be resolved by recrystallization from absolute ethanol. Acidification of the resolved diastereomeric ammonium salts with methanesulfonic acid and extraction furnishes both epoxy acid enantiomers in eantiomerically pure form. Because the optical rotation and absolute configuration of one of the antipodes was known, the identity of enantiomerically pure epoxy acid, (+)-27, with the absolute configuration required for a synthesis of erythronolide B, could be confirmed. Sequential treatment of (+)-27 with ethyl chloroformate, excess sodium boro-hydride, and 2-methoxypropene with a trace of phosphorous oxychloride affords protected intermediate 28 in an overall yield of 76%. The action of ethyl chloroformate on carboxylic acid (+)-27 affords a mixed carbonic anhydride which is subsequently reduced by sodium borohydride to a primary alcohol. Protection of the primary hydroxyl group in the form of a mixed ketal is achieved easily with 2-methoxypropene and a catalytic amount of phosphorous oxychloride. [Pg.176]

Sodium borohydride is a much milder reducing agent than lithium aluminium hydride and like the latter is used for the reduction of carbonyl compounds like aldehydes and ketones. However, under normal conditions it does not readily reduce epoxides, esters, lactones, acids, nitriles or nitro groups. [Pg.289]

The stereoselective epoxidation of chalcones, followed by acid-catalysed ring closure and concomitant cleavage of the epoxide ring, provides a very efficient route to chiral flavon-3-ols and, subsequently, by borohydride reduction to produce flavan-3,4-diols [13, 14], It has been shown that diastereoselective reduction of the chiral flavon-3-ols by sodium borohydride in methanol yields the trans-2,3-dihydroxy compounds, whereas borohydride reduction in dioxan produces the cis-isomers [14] the synthetic procedure confirms the cis configuration of the 2,3-hydroxy groups of naturally occurring leucodelphinidins [14]. [Pg.538]

In 23-cpoxybutyric acid sodium borohydride opened the epoxide ring without affecting the carboxyl. Varying ratios of 2- and 3-hydroxybutyric acid were obtained depending on the reaction conditions. Sodium borohydride in alkaline solution gave 18% of a- and 82% of -hydroxybutyric acid while in the presence of lithium bromide the two isomers were obtained in 60 40 percentage ratio [1000]. [Pg.143]

To summarize, crystalline l,4-dideoxy-l,4-imino-hexitols are readily prepared from 2,6-dibromo-2,6-dideoxy-hexonolactones in gram quantities without any use of chromatographic separations. The bromolactones may, prior to treatment with aqueous ammonia, either be converted into the 2,3-epoxides by treatment with KF or K2CO3 in acetone, or may be reduced with sodium borohydride in water to give the bromodeoxyhexitols. [Pg.133]

The third method makes use of the one-flask procedure, which is advantageous from the preparative point of view. However, opening of certain stereoisomeric epoxides (263) with selenophenol suffers from low regioselectivity, resulting in a low yield of the final product. The other disadvantage is the basic reaction-medium occasioned by the method used for the generation of selenophenol, namely reduction of diphenyl diselenide with sodium borohydride in solution in anhydrous alcohol (see Ref. 356) some epoxides are sensitive to basic media. However, David (see Ref. 356) did not observe side reactions in his syntheses of 256. [Pg.53]

Sodium borohydride, 278 Sodium cyanoborohydride-Zinc iodide, 280 of epoxides... [Pg.363]

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... [Pg.372]

While successful demercuration using alkaline sodium borohydride has been reported, this process can also give rise to epoxides (equation 240).383 Tri-n-butyltin hydride often gives improved results.384... [Pg.306]

Several alkenyl hydroperoxides have been successfully cyclized to five-, six- and seven-membered ring peroxides (equation 241).38s 388 Alkaline sodium borohydride reduction of these mercurials is frequently accompanied by epoxide or cyclic ether formation. [Pg.306]

Alkyl hydroperoxides. Peroxymercuration of alkenes proceeds cleanly and in good yield. These products previously were reduced to the desired alkyl hydroperoxides with alkaline sodium borohydride. This reduction proceeds in reasonable yield in the case of terminal alkenes, but scission to form epoxides of the original alkene predominates among products from nonterminal alkenes. This difficulty is now overcome by use of tri-n-butyltin hydride for reduction.18... [Pg.617]

In the alternate and unsuccessful approach to haemanthidine (382), which entailed the construction of the D ring prior to the functionalization of the C ring, the ester 458 was converted to the unsaturated keto lactam 468 by a straightforward route analogous with the one discussed above for the transformation of 461 to 463. The carbonyl group at C-6 was then reduced with sodium borohydride to alleviate concern over its reactivity, but epoxidation of the double bond at C-2 and C-3 of 469 afforded a mixture of diastereomeric a- and (3-epoxides. Owing to the lack of stereoselectivity in this crucial step, this route was abandoned (202). [Pg.340]


See other pages where Epoxides sodium borohydride is mentioned: [Pg.28]    [Pg.42]    [Pg.33]    [Pg.31]    [Pg.45]    [Pg.104]    [Pg.197]    [Pg.355]    [Pg.52]    [Pg.1080]    [Pg.357]    [Pg.293]    [Pg.231]    [Pg.133]    [Pg.136]    [Pg.137]    [Pg.865]    [Pg.24]    [Pg.57]    [Pg.73]    [Pg.19]    [Pg.133]    [Pg.136]    [Pg.137]    [Pg.22]    [Pg.29]    [Pg.315]    [Pg.376]    [Pg.273]    [Pg.279]    [Pg.273]    [Pg.294]   
See also in sourсe #XX -- [ Pg.874 ]

See also in sourсe #XX -- [ Pg.8 ]

See also in sourсe #XX -- [ Pg.8 ]




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