And sodium borohydride reduction

The carbonyl group of carbohydrates can be reduced to an alcohol function. Typical procedures include catalytic hydrogenation and sodium borohydride reduction. Lithium aluminum hydride is not suitable, because it is not compatible with the solvents (water, alcohols) that are requited to dissolve caibohydrates. The products of caibohydrate reduction aie called alditols. Because these alditols lack a car bonyl group, they aie, of course, incapable of forming cyclic hemiacetals and exist exclusively in noncyclic forms. 

Several syntheses of secoquettamines have been performed. Seco compounds 234 and 235 were semisynthesized from quettamine (236) by Hofmann and Emde degradations, respectively (179). Chattopadhyay and Shamma (184) conducted a total synthesis of these bases with the intermediacy of quettamine (236) (Scheme 36). In this approach Reissert compound 237 served as substrate. On reaction with 4-benzyloxybenzaldehyde 237 supplied the addition product 238, which after N-methylation and sodium borohydride reduction afforded amino carbinol 239. Compound 239 was cyclized to... 

Similarly to 8-lactone 260, y-lactone 263, prepared also from ( )-norcamphor (228), proved to be another useful intermediate for the synthesis of all four corynantheidol stereoisomers as well as of the corresponding 18,19-didehydro derivatives. Cleavage of the a-diketone monothioketal moiety in 263 and the formation of amide 265 by its reaction with tryptamine, followed by Bischler-Napieralski cyclization and sodium borohydride reduction, resulted in a mixture... 

The second approach (224-226) employs O-methylhexadehydroyohimbine (420), prepared from spiroindeno-2-(l -tetrahydro-0-carboline)-l-onederivative 416 by photolysis and subsequent reduction, as the key intermediate. The side product (418) of the photolysis was also utilized for the preparation of 420 via subsequent phosphoryl chloride treatment and sodium borohydride reduction. Birch reduction of 420 resulted in enol ether 421, which could be transformed to 15,16-didehydroyohimbinone (410), prepared previously by Szantay et al. (74, 221) as a universal precursor of the synthesis of yohimbine-type alkaloids. 

Hydride as nucleophile lithium aluminium hydride and sodium borohydride reductions... 

Reduction of ketones. Reduction of ketones with metals in an alcohol is one of the earliest methods for effecting reduction of ketones, and is still useful since it can proceed with stereoselectivity opposite to that obtained with metal hydrides.1 An example is the reduction of the 3a-hydroxy-7-ketocholanic acid 1 to the diols 2 and 3. The former, ursodesoxycholic acid, a rare bile acid found in bear bile, is used in medicine for dissolution of gallstones. The stereochemistry is strongly dependent on the nature of the reducing agent (equation I).2 Sodium dithionite and sodium borohydride reductions result mainly in the 7a-alcohol, whereas reductions with sodium or potassium in an alcohol favor reduction to the 7p-alcohol. More recently3 reduction of 1 to 2 and 3 in the ratio 96 4 has been achieved with K, Rb, and Cs in f-amyl alcohol. Almost the same stereoselectivity can be obtained by addition of potassium, rubidium, or cesium salts to reductions of sodium in t-amyl alcohol. This cation effect has not been observed previously. 

While the condensation of enamine 37 with methyl OY7 s-2-butenoate, followed by acid hydrolysis and sodium borohydride reduction affords lactone 38 with reasonable efficiency, the cyclodehydrative ring contraction of this intermediate with PPA gives a mixture of bicyclo[3.3.0]octenones in abysmal (< 5 %) yield.66 To circumvent this difficulty and enable the large scale production of 39,2-carbo-methoxy-4,4-dimethylcyclohexanone was initially transformed to tram diacid 40 under Favoiskii conditions (Scheme 14). Conversion to the diacid chloride and condensation with lithium dimethylcuprate resulted in formation of the diacetyl derivative. In basic solution, the latter is reported to experience epimerization and aldol cyclization with dehydration in 82 % yield. With hydrogen and palladium on charcoal, the essentially quantitative production of 39 was achieved.66 ... 

Treatment of the compounds 78 with various alkyl halides in the presence of sodium hydride results in 1-alkylation as with normal Reissert com-pounds. ° Acylation has also been reported under these conditions. Under a variety of conditions, however, 78 does not react with benzaldehyde. Acid hydrolysis of 80 gave tetrahydroquinaldic acid, while acid hydrolysis of the alkylated dihydroisoquinoline-Reissert compounds gave the amino acids 81. By first complexing the alkylated dihydroisoquinoline-Reissert compound with zinc chloride in ether and then hydrolyzing the complex, the nitrile was hydrolyzed to an acid, but the amide group was left intact. The perchlorate salts of dihydroisoquinoline-Reissert compounds have also been prepared, and sodium borohydride reduction proceeds in the same manner as reduction of the Reissert salt to... 

The carbonyl group of carbohydrates can be reduced to an alcohol function. Typical procedures include catalytic hydrogenation and sodium borohydride reduction. Lithium aluminum hydride is not suitable, because it is not compatible with the solvents (water,... 

Periodate promoted cleavage of vicinal diols has also been used to prepare monocyclic products. Oxabicyclo[4.2.1]nonadiene 116 derived from diiodoke-tone 77 was subjected to sodium periodate and sodium borohydride reduction to generate 117, Eq. 87. Subsequent elaborations resulted in the stereocontrolled synthesis of oxepine 118, a subunit designed for the assembly of polyether toxins such as ciguatoxin [135]. 

Martinez and Joule (273) have described a very general route to the 6//-pyrido[4,3-ft]carbazole system involving y-aminoenone intermediates. Ketalization of 682 followed by indole N-methylation, pyridine N-methylation, and sodium borohydride reduction afforded 683. Mannich condensation gave a product which was hydrolyzed to the y-aminoenone 684. When 684 was refluxed in 50% aqueous acetic acid the hydroxy tetrahydro 6//-pyrido[4,3-Z> Jcarbazole 685 was produced in 25% yield. 

Condensation between tetra-O-acetyl-a-D-galactopyranosyl bromide and a suitably protected 2-acetamido-2-deoxy-0 -D-galactopyranosyl-L-serine derivative gave access to compound (48) which is the JV-tosyl derivative of the carbohydrate core of mucins and was required for studies of haemagglutination. Evidence that the major glycoprotein of TA3-Ha tumour cells contains the same disaccharide was produced by the isolation, after alkaline degradation and sodium borohydride reduction, of 2-acetamido-2-deoxy-3-On 3-D-galacto-... 

The bioactive core aldehydes derived from the oxidation of LDL phospholipids (see Section E.2) can be analysed either directly by LC-MS or after hydrolysis by phospholipases and sodium borohydride reduction. These aldehyde esters are purified by solid-phase extraction followed by preparative TLC. Unwanted ester containing phospholipids can be removed after treatment with phospholipase Al. The more polar oxidized phospholipids are eluted by HPLC after the class of phospholipids from which they are derived. The core aldehydes derived from oxidized phospholipids (Section E.2) are also known to be pro-inflammatory. Only a few C-4 and C-5 core aldehydes have been identified and analysed by LC-MS, either directly or after derivatization in oxidized LDL. Many more saturated and unsaturated core aldehydes can be expected in oxidized LDL, according to the degree and mode of oxidation. However, the abihty of these core aldehydes to form covalent adducts with the apoB of LDL may prevent them from being detected directly by LC-MS. Chemical or enzymatic hydrolysis may therefore be required before they can be analysed by this technique. 

Chen s stereospecific total synthesis of cycloeudesmol 48 started with the hydrazone 46, which was converted to the allylic alcohol 47 by the Bamford-Stevens reaction followed by DMF trapping of the vinyl anion and sodium borohydride reduction. This allylic alcohol 47 was then taken on through a further ten steps to yield the natural product cycloeudesmol 48. 

Lanthanide chlorides and sodium borohydride reductions of unsaturated ketones... 

The synthesis of retronecine was completed using a 4-reaction sequence. The C3 hydroxyl group of 34 was converted to a mesylate which underwent j8-elimination to introduce the C1-C2 olefin. The acetal of 35 was hydrolyzed, and sodium borohydride reduction of the C7 ketone from the convex face provided 37. 1,2-Reduction of the unsaturated ester using alane finished the synthesis of retronecine (21). 

The furanosides 1 and 4 react with magnesium methoxide to give the annelated cyclopropanes 2 and 5, and sodium borohydride reduction followed by detrityla-tion affords 3 or 6 and 7 (Scheme 1). The reaction of 1 proceeds via an elimination occurring within intermediate 8, to generate magnesium enolate 9, which is internally alkylated by displacement of the CS tosylate. ... 

The route commenced with the condensation of amine 229 and carboxylic acid 230 at 200 °C. Subsequent Bischler-Napieralski reaction and sodium borohydride reduction established the C/D ring system of morphine and delivered tetrahydroisoquinoline 231 in good yield. Next, Birch reduction and Af-formylation afforded enol ether 232, which was converted into the corresponding ketal before reaction with bromine allowed the isolation of the cyclization precursor. The halide in 233 serves to protect the para position in the aromatic ring in the subsequent acid-mediated electrophilic cyclization reaction—a common strategy that has also been applied by other research groups in their endeavors toward morphine and related alkaloids. 

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