Sodium borohydride, reduction of carbonyl

Alumina-sodium borohydride, reduction of carbonyl compounds with, 16 572-573 Alumina sols, gelation of, 23 77 Alumina-supported iodobenzene diacetate (IBD), 16 570... 

Sodium borohydride and lithium aluminum hydride react with carbonyl compounds in much the same way that Grignard reagents do except that they function as hydride donors rather than as carbanion sources Figure 15 2 outlines the general mechanism for the sodium borohydride reduction of an aldehyde or ketone (R2C=0) Two points are especially important about this process... 

Nucleophilic addition to carbonyl groups sometimes leads to a mixture of stereoisomeric products The direction of attack is often controlled by stenc factors with the nude ophile approaching the carbonyl group at its less hindered face Sodium borohydride reduction of 7 7 dimethylbicyclo[2 2 IJheptan 2 one illustrates this point... 

The final stages of the successful drive towards amphotericin B (1) are presented in Scheme 19. Thus, compound 9 is obtained stereoselectively by sodium borohydride reduction of heptaenone 6a as previously described. The formation of the desired glycosida-tion product 81 could be achieved in dilute hexane solution in the presence of a catalytic amount PPTS. The by-product ortho ester 85 was also obtained in approximately an equimolar amount. Deacetylation of 81 at C-2, followed sequentially by oxidation and reduction leads, stereoselectively, to the desired hydroxy compound 83 via ketone 82. The configuration of each of the two hydroxylbearing stereocenters generated by reduction of carbonyls as shown in Scheme 19 (6—>9 and 82->83) were confirmed by conversion of 83 to amphotericin B derivative 5 and comparison with an... 

The roots of Thalictrum rochebrunianum Franc, and Sav. (Ranunculaceae) yielded dihydrothalictrinine (142), mp 194-197°C, C38H3gN209, [a]j=,2 -125° (c 0.13, MeOH) (81). The NMR spectrum resembles that of thalictrinine (143, Section II,C,114), but shows broadening of the protons on the monosubstituted benzyl ring. The IR spectrum lacks the carbonyl and shows a hydroxy absorption at 3280 cm-1. Sodium borohydride reduction of thalictrinine gave dihydrothalictrinine as the sole product in high yield. From consideration of steric factors, 142 was suggested as the structure of dihydrothalictrinine (12,81). 

Reduction is commonly employed to convert imino and oxo bisbenzyliso-quinoline alkaloids to identifiable derivatives, or to other alkaloids. Thus thalsimine (58) gave, with either Zn/H2S04 or NaBH4, a mixture of norheman-dezine (234) and its epimer (391) (81). Sodium borohydride reduction of thalictrinine (Section II,C,114) gave specifically dihydrothalictrinine (Section II,C,31), from attack at the less hindered side of the carbonyl (81). 

Carnavoline, C18H37NO2 (mp 66.7°-67.2°), isolated along with cassine from Cassia carnaval Spreg., is the diol (CXX) resulting from the reduction of the carbonyl group in cassine 182). Sodium borohydride reduction of cassine gives carnavoline. 

Another pathway involved sodium borohydride reduction of the carbonyl group at C-9 in (246d), affording the lactone (251). Reduction with lithium aluminium hydride and boron trifluoride etherate or with hydrogen and platinum oxide in acetic acid led to the 11-oxapregnane (252), which was readily converted into the diketone (253). ... 

Commercial hexythiazox is a racemic mixture of the two trans enantiomers Scheme 26.2.2 shows the main synthetic pathways [11, 17, 19]. Starting from 4-chloro propiophenone the key intermediate erythro amino alcohol may be obtained by stereoselective catalytic reduction of the corresponding hydroxy imi-noketone or by sodium borohydride reduction of the aminoketones obtained via Gabriel synthesis. Different routes lead from this aminoalcohol to the trans-thiazolidinone system the basis of all routes is activation of the hydroxy group, e.g., in form of the sulfonate and a ring forming reaction with carbon disulfide or carbonyl sulfide. The final acylation of the NH group with cyclohexyl isocyanate leads to hexythiazox. 

The first two entries in Table 23.2 illustrate reactions that involve nucleophilic addition to the carbonyl group of the open-chain form which, although present in small amounts, is continuously replenished as it reacts. Entry 1 is the sodium borohydride reduction of the carbonyl group of the aldose o-galactose. The reaction is a general one other... 

General Synthesis and Reactions.—Linear primary alcohols with at least seven carbon atoms are transformed into esters in high yield using copper oxide at temperatures above 170 C in the liquid phase. RusfCO) catalyses the conversion of an aldehyde, or an alcohol with the same number of carbon atoms, into an ester in the presence of diphenylacetylene. " The carbonylation of organic halides in the presence of cyclic ethers is catalysed by PhPdI(PPh3)2 , it provides a synthesis of halohydrin esters in reasonable yield. Cyanohydrin esters have been synthesized by the sodium borohydride reduction of acyl cyanides in the presence of tetra-n-butylammonium bromide. ... 

Carbonyl Group Reduction. The flow of new methods for reduction of acid derivatives and aldehydes or ketones to alcohols continues unabated. The Report last year (4,134) featured the sodium borohydride reduction of carboxylic acid derivatives, originally thought to be 2-thiazoline-2-thiol esters (14), to give alcohols in good yields. Full details of the method have now appeared (Scheme 8), and it seems that the acid derivatives are in fact the 3-acyl thiazolidine-2-thiones (IS) dissappearance of their yellow colour is an easy way to monitor the reduction. Carboxylic acids or their chlorides can also be reduced to primary alcohols in good yields at room temperature using a titanium tetrachloride-sodium borohydride combination. ... 

The well-known reduction of carbonyl groups to alcohols has been refined in recent studies to render the reaction more regioselective and more stereoselective Per-fluorodiketones are reduced by lithium aluminum hydride to the corresponding diols, but the use of potassium or sodium borohydride allows isolation of the ketoalcohol Similarly, a perfluoroketo acid fluonde yields diol with lithium aluminum hydnde, but the related hydroxy acid is obtainable with potassium borohydnde [i f] (equations 46 and 47)... 

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. 

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