Reductive work

Conceptually closely related, cefroxadi ne (40) can be prepared by several routes, including one in which the enol (33) is imethylated with diazomethane as a key step. A rather more involved route starts with comparatively readily available phenoxymethylpenicillin sulfoxide benzhydryl ester (36). This undergoes fragmentation when treated with benzothiazole-2-thiol to give Ozonolysis (reductive work-up) cleaves the... 

Since ketone (5) is available (Tl) and the extra methyl groups will be removed in the ozonolysis, this was the starting material for the published synthesis. Reductive work-up (zinc was used) for the ozonolysis is necessary to preserve the aldehyde. 

The chemoselectivity of the ozonolysis is all right because ozone attacks the most electron-rich double bond, that is the one furthest from the carbonyl group in (17, R=H). Reductive work-up is again needed after the ozonolysis,... 

The synthesis was carried out by the Diels-Alder addition and ozonolysis with reductive work-up. No... 

An alternative approach (Scheme 2) to polyoxyfunctionalised azepines (eg. 9) involves cyclooctatetraene as a starting material via its la, 2a, 5a, 6a -diepoxy-3(3,4(S-diol 7, and subsequent amine nucleophilic attack to give 8 followed by ozonolysis with reductive work up to afford 9 <00TL5483>. 

The cuprate derived from the cis isomer of this reagent undergoes conjugate addition with cyclohexenone with unusually high diastereoselectivity (5 1, Eq. 23)24). In this case, electrophilically initiated ring opening with mercuric acetate chemo-selectively attacks the sterically least hindered cyclopropyl bond to give a branched product 7. Reductive work-up produces 8 in which the stereochemistry of the... 

The ozonolysis of cyclobutene derivatives in the preparation of 1,4-diketones was also applied to the total synthesis of eyclopentanoid antibiotics 161 162k The oxidative cleavage of (470) by ozone and reductive work-up yielded the diketone (471) in 73 % yield. Diketone (471) underwent intramolecular aldol cyclization to give the key intermediate (472), which was used to synthesize ( )-xanthocidin161,162), (+)-epi-xanthocidin 162), ( )-p-isoxanthocidin161,162) as well as ( )-desdihydroxy-4,5-didehydroxanthocidin162). 

The methoxycylobutene (473) also underwent ozonolysis in the presence of MeOH and yielded (474) after reductive work-up with S02 163). The cyclopentane derivative (474) was finally converted to ll-deoxy-PGEx 163). 

Organolithium or Grignard compounds derived from aryl or heteroaryl halides react with diphenyl phosphorazidate to give labile phosphinoyltriazenes, which on reductive work-up with aluminium hydride afford good yields of aryl or heteroaryl amines (equation 7)34. 

The stoichiometric ADH of olefins was performed by adding 1 equiv. of olefin to a 1 1 mixture of Os04 and 4a in dry toluene (O.IM in 4a), followed by reductive working-up with LAH to give the () ,) )-diol in 60-95% yield and good to excellent ee. 

A further improvement resulted when potassium hexacyanoferrate(III) was used as secondary oxidant (Table 10.4, entries 5 and 6), in which case the slow addition of olefin was not necessary. O Chemical yields of 85-90% and ee of 89% were obtained by adding at room temperature 0.0025 equiv. of OSO4 to a mixture of 1 equiv. of ( )-3-hexene, 0.25 eq of 4a or 4b, 3 equiv. of K3Fe(CN)6 and 3 equiv. of K2CO3 in rert-butyl alcohol-water (1/1, v/v), followed by reductive working-up with N32S03. 

In their pioneering work. Just and co-workers have described many interesting transformations of the Diels-Alder adducts of furan to methyl nitroacrylate (77 + 77 ) and to dimethyl acetylenedicarboxylate (53). The mixture of racemic adducts 77 + 77 was hydroxylated into the exo-cis-diols 125 + 125 , separable by crystallization. Treatment of the isopropylidene acetal obtained from 125 with diazabicyclo[5.4.0]undec-5-ene (DBU) gave a high yield of alkene 126. Ozonolysis followed by a reductive work-up with dimethylsulfide, then with NaBH4, gave a mixture of epimeric triols 127. Cleavage with sodium periodate afforded 2,5-anhydro-3,4-0-isopropylidene-DL-allose (128) in 15 % yield, based on methyl 2-nitroacrylate used. TTie same allose derivative was obtained from adduct 53. ... 

A stereoselective cyclization of (Z)-(2R,3R,4R)-6-cyclohexyloxy-1,3,4-tribenzyloxy-5-hexen-2-ol promoted by mercuric trifluoroacetate or PhSeCl is successfully achieved (38). 2-Deoxy-0(-hexopyranoside derivative is obtained almost exclusively by the treatment of 22 with mercuric trifluoroacetate followed by reductive work up, while a predominant formation of the 3 3no 6r is achieved by the reaction of 22 with PhSeCl, and the successive deselenylation. 

There are two syntheses of isoquinolines from indenes by oxidation and subsequent addition of ammonia or ammonium salts, differing only in oxidizing medium. Both are summarized in equation (76) in the first, ozonolysis with a reductive work-up is used (80JOC5312), in the second, periodate and catalytic amounts of osmium tetroxide (81JOC4999). The yields can be very good. 

Azadienes of this sort were studied simultaneously by Mariano et al., who reacted mixtures of (1 ,3 ) and (1E, 3Z)-l-phenyl-2-aza-l,3-pentadiene 275 with several electron-rich alkenes, e.g., enamines and enol ethers (85JOC5678) (Scheme 61). They found the (l ,3 )-stereoisomer to be reactive in this process affording stereoselectively endo 276 or exo 277 piperidine cycloadducts in 5-39% yield, after reductive work-up with sodium borohydride. The stereochemistry of the resulting adducts is in agreement with an endo transition state in the case of dienophiles lacking a cis alkyl substituent at the /8-carbon (n-butyl vinyl ether, benzyl vinyl ether, and 1-morpholino cyclopentene), whereas an exo transition state was involved when dihydropyrane or c/s-propenyl benzyl ether were used. Finally, the authors reported that cyclohexene and dimethyl acetylenedi-carboxylate failed to react with these unactivated 2-azadienes. 

The treatment of an alkene by 5yn-hydroxylation, followed by periodic acid (HIO4) cleavage, is an alternative to the ozonolysis, followed by reductive work-up. 5yn-diols are oxidized to aldehydes and ketones by periodic acid (HIO4). This oxidation reaction divides the reactant into two pieces, thus it is called an oxidative cleavage. 

Alkenes can be cleaved by ozone followed by an oxidative or reductive work-up to generate carbonyl compounds. The products obtained from an ozonolysis reaction depend on the reaction conditions. If ozonolysis is followed by the reductive work-up (Z11/H2O), the products obtained are aldehydes and/or ketones. Unsubstituted carbon atoms are oxidized to formaldehyde, mono-substituted carbon atoms to aldehydes, and di-substituted carbon atoms to ketones. 

Alkenes are directly oxidized to aldehydes and/or ketones by ozone (O3) at low temperatures (—78 °C) in methylene chloride, followed by the reductive work-up. For example, 2-methyl-2-butene reacts with O3, followed by a reductive work-up to yield acetone and acetaldehyde. This reducing agent prevents aldehyde from oxidation to carboxylic acid. 

Ozonolysis of alkynes followed by hydrolysis gives similar products to those obtained from permanganate oxidation. This reaction does not require oxidative or reductive work-up. Unsubstituted carbon atoms are oxidized to CO2, and mono-substituted carbon atoms to carboxylic acids. For example, ozonolysis of 1-butyene followed by hydrolysis gives propionic acid and carbon dioxide. 

On treatment of furan at low temperature with hydrogen peroxide the peroxide (53) is obtained which may be partially hydrogenated to malealdehyde. 2,5-DimethyIfuran with acidic hydrogen peroxide yields the hydroperoxide (54) and the cyclic peroxides (55) and (56) mechanisms have been proposed. Ozonolysis of furan at -60 °C in chloroform with reductive work up affords glyoxal and formic acid. Methylfurans behave similarly thus... 

The quantization and coding tools in an encoder do the main data-reduction work. As in the case of filter banks, a number of design options are possible and have been explored. 

Ozonolysis allows the cleavage of alkene double bonds by reaction with ozone. Depending on the work up, different products may be isolated reductive work-up gives either alcohols or carbonyl compounds, while oxidative work-up leads to carboxylic acids or ketones. 

But this does not make 5 instead it makes 1 with an extra carbon atom. So what we need are oxidative methods to convert 1 into 5 by cleavage of the alkene. There are many ways to do this. The most obvious is ozone1 that gives aldehydes from a disubstituted alkene 6 with reductive work-up or acids with oxidative work-up. 

The synthesis5 follows this pattern with ozone and reductive work-up with dimethyl sulfide ensuring that the aldehyde is not further oxidised and deprotection of 30 taking place after the Wittig reaction. 

Ozonolysis of the double bond in 1,4-cyclohexadiene 943 followed by reductive work-up and dehydration provides the dihydropyran-4-one 944, an intermediate during a formal synthesis of leucascandrolide (Equation 369) <2002CC2066>. 

Scheme 13 Option. A great deal of work was carried out to find a reduction procedure for the chiral reduction of the readily available R-aminoketone (IX). In addition, despite the benzyl blocking group, the R-aminoketone (XVII) was also the subject of chiral reduction work.

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