Secondary alcohols borohydride

Reduction to alcohols (Section 15 2) Aide hydes are reduced to primary alcohols and ketones are reduced to secondary alcohols by a variety of reducing agents Catalytic hydrogenation over a metal catalyst and reduction with sodium borohydride or lithium aluminum hydride are general methods... 

Finally in this section on deracemization via cyclic oxidation/reduction methods, there has been some limited work carried out on the deracemization of secondary alcohols. Soda et al. [22] employed lactate oxidase in combination with sodium borohydride to deracemize D/i-lactate (18) via the intermediate pyruvate (19) (Figure 5.12). 

By reduction of aldehydes and ketones Aldehydes and ketones are reduced to the corresponding alcohols by addition of hydrogen in the presence of catalysts (catalytic hydrogenation). The usual catalyst is a finely divided metal such as platinum, palladium or nickel. It is also prepared by treating aldehydes and ketones with sodium borohydride (NaBH4) or lithium aluminium hydride (LLAIH4). Aldehydes yield primary alcohols whereas ketones give secondary alcohols. 

Reduction of the ketones 44a and 46 with sodium borohydride gave the secondary alcohols 49 and 50, respectively, in high yield. ... 

Strong reducing agents like sodium borohydride and lithium aluminum hydride are capable of reducing aldehydes to primary alcohols and ketones to secondary alcohols. The general reaction is the reverse of the reactions used to form aldehydes and ketones by the oxidation of primary and secondary alcohols, respectively (to review, see the earlier section Oxidation reactions ). However, the mechanisms for reduction are different. 

Reduction of a ketose yields a secondary alcohol, and reduction of an aldose yields a primary alcohol (ccilled an alditol). A possible reducing agent is hydrogenation in the presence of a catalyst, such as platinum another reducing agent is sodium borohydride (NaBH ) followed by hydrolysis. Figure 16-14 illustrates the formation of an alditol. 

Treatment of the ketone (258a) with formaldehyde in the presence of sodium bicarbonate gives the alcohol (258b), the keto group of which is readily reduced by sodium borohydride to the corresponding secondary alcohol.218... 

Aldehydes and ketones are conveniently reduced by sodium borohydride, which is much milder than LAH and does not require aprotic conditions (an alcohol is often the preferred reaction solvent). Aldehydes give primary alcohols while ketones give secondary alcohols. 

Oxy-Cope rearrangement. Tertiary 1,5-hexadiene-3-ols undergo oxy-Cope rearrangement at room temperature on treatment with 1 equiv. of mercury(II) trifluoroacetate and subsequent demercuration with sodium borohydride.2 The corresponding secondary alcohols undergo polymerization in the presence of this salt. 

In the second step the carbonyl group of the a-bromo ketone is reduced to a secondary alcohol. As actually carried out, sodium borohydride in water was used to achieve this transformation. 

Aldehydes and ketones are easily reduced to primary or secondary alcohols, respectively. Useful reagents for this purpose are various metal hydrides such as lithium aluminum hydride (LiAIH4) or sodium borohydride (NaBH4). 

Aldehydes and ketones when reduced yield alcohols with a hydride ion that is provided by reducing reagents like sodium borohydride or lithiumborohydride. Primary alcohols are obtained from aldehydes and secondary alcohols from ketones. 

Sodium borohydride (NaBH4) reduces aldehydes to primary alcohols, and ketones to secondary alcohols. The reactions take place in a wide variety of solvents, including alcohols, ethers, and water. The yields are generally excellent. 

Lithium aluminum hydride (LiAlH4, abbreviated LAH) is a much stronger reagent than sodium borohydride. It easily reduces ketones and aldehydes and also the less-reactive carbonyl groups those in acids, esters, and other acid derivatives (see Chapter 21). LAH reduces ketones to secondary alcohols, and it reduces aldehydes, acids, and esters to primary alcohols. The lithium salt of the alkoxide ion is initially formed, then the (cautious ) addition of dilute acid protonates the alkoxide. For example, LAH reduces both functional groups of the keto ester in the previous example. 

P-Keto sulfoximines 300 undergo diastereoselective reductions at -78 °C with sodium borohydride or diborane to give mixtures of diastereomeric P-hydroxy sulfoximines. The product diastereoselection increases as the steric demand of the substituent R of 300 increases (Table 19). Reductive removal of the P-sulfoximine group of the diastereomeric mixture of P-hydroxy sulfoximines gives secondary alcohols with the (S)-configuration.125... 

Conversion of esters to secondary alcohols The reaction of esters with Grignard reagents results mainly in tertiary alcohols, which are formed by way of an intermediate ketone. Direct conversion of an ester to a secondary alcohol is possible by reaction with a Grignard reagent (2 equiv.) and lithium borohydride (0.5 equiv.), which reduces the intermediate ketone much more rapidly than it does the ester. 

When relais substance 431 was selectively dehydrated via the triflate of the secondary alcohol the path toward coiianin (21) was opened (Scheme 50). The authors used the fact that neighboring hydroxy groups enhance the reducing power of borohydrides to selectively reduce one of the lactones to the hemiacetal 434. Reduction to tetrahydrofuran 435 was achieved by thioacetal formation with... 

Mitsunobu reaction as well as by mesylation and subsequent base treatment failed, the secondary alcohol was inverted by oxidation with pyridinium dichromate and successive reduction with sodium borohydride. The inverted alcohol 454 was protected as an acetate and the acetonide was removed by acid treatment to enable conformational flexibility. Persilylation of triol 455 was succeeded by acetate cleavage with guanidine. Alcohol 456 was deprotonated to assist lactonization. Mild and short treatment with aqueous hydrogen fluoride allowed selective cleavage of the secondary silyl ether. Dehydration of the alcohol 457 was achieved by Tshugaejf vesLCtion. The final steps toward corianin (21) were deprotection of the tertiary alcohols of 458 and epoxidation with peracid. This alternative corianin synthesis needed 34 steps in 0.13% overall yield. 

The first step, a 1,3-dipolar addition, results in the formation of a primary ozonide (1 equation 6). This intermediate then opens to give a carbonyl and a zwitterion that can recombine to give the more stable normal ozonide (2 equation 7). Reduction of (2), without isolation, by lithium aluminum hydride, diborane or sodium borohydride dten gives either primary or secondary alcohols, depending on the nature of starting alkene (equation 8). 

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