Reduction Using NaBH

As introduced in Section 2.2.4, monobenzylic alcohols are inherently poor substrates for reduction using NaBH TFA. However, notable exceptions have been discovered and this tactic has a synthetic niche as illustrated with reduction products 101-105. Diastereo-selective introduction of deuterium was reported in the studies involving tetrahydroisoquinoline 102.89 Note that alkene formation from the carbocation intermediates... 

Some of the more common reductions using NaBH are given (Scheme 100). 

The inorganic reductions of NaBH are numerous and varied (Table 7). Comparatively few anions are reduced, yet the reduction of bisulfite to dithionite (hydrosulfite) (25), which is used in the pulp (qv) and paper (qv), clay (see Clays), and vat dyeing industries, is an important inorganic appHcation ofNaBH,. 

The Ag nanoparticles were synthesized by the reduction of Ag ions in the water core of the AOT/F-pentanol (AOTF) w/c RMs using NaBH(OAc)3. The acidic nature of the water core due to the formation of carbonic acid makes conventional reagents such as NaBH4 and... 

Microwave-induced imine formation, subsequent reduction with NaBH(OAc)3 and cyclisation of the resulting amino acid with isothiocyanates was used in an efficient one-pot multi-step synthesis of thiohydantoins (Scheme 4.26). The reductive animation was conducted as a two-step procedure to avoid direct reduction of the aldehyde at high temperatures48. 

Prepared by treatment of W-Boc-aspartic acid p-methyl ester with /V-hydroxysuccinimide in the presence of N,N-dicyclohexylcarbodiimide,21 reduction with NaBH, in aqueous THF, and conversion into the iodide using PPh3, l2, and imidazole.22... 

Figure 3.50 Synthesis of a chiral amino functionalised NHC ligand by reduction of a chiral imino functionalised imidazolium salt using NaBH. ...

Methylstibine and MCjSbH form from reaction of MCjSbBr with NaBH in diglyme. From the cleaner reduction using LiBH(OCH3)j ... 

Oxidations and reductions. Phase-transfer catalyst enables the oxidation of benzylamines to benzamides with KMnO in an organic solvent, whereas reduction of aldehydes can be carried out in toluene using NaBH and polyethylene glycol. ... 

In alcoholic medium, NaBH, converts a,P-unsaturated nitriles into cyanoethyl compounds under more severe conditions (refluxing alcohol for several hours). - i jpig enantioselective reduction of the double bond of each ( )- and (Z)-isomer of a,P-unsaturated nitriles derived from ketones has been evaluated using NaBH in EtOH/diglyme in the presence of semicorrin (/oCT catalyst the yields are good (about 75%), but the enantioselectivity remains modest (53-69%). - In contrast, it has been found that copper(l) hydride, a reagent that presumably operates by a mechanism akin to the Michael reaction, 754 cleanly and stereoselectively effects the reduction of a,P-iinsaturatcd to saturated nitriles in the presence of 2-butanol, as proton donnor, in THE. The use of LAH in THF at room temperature has also been reported in the stereoselective reduction of a,P-iinsaturatcd nitriles. 

C12H24O Mr 184.32, is a mixture of isomers where one of the dashed lines represents a carbon-carbon double bond, the others a single bond. None of the compounds occur in nature. It is a colorless to slightly yellow liquid, df1 0.864-0.872, rej3° 1.454-1.460, with a fine woody, ambra, dry odor with a clean vetivert character. Synthesis starts from 2-methyl-2-butene (isoamylene) which is dimerized and the product acetylated to give the corresponding hepten-2-ones (see p. 18). The hepten-2-ols are obtained by reduction with NaBH [13]. The mixture is used in perfume compositions, for example, for detergents. 

Similar results were observed in the synthetic efforts toward the C16-C27 segment of bryostatin l.25 The synthesis of the fragment utilized a Luche reduction as the final step. This particular reaction using NaBH and CeCb reduced from the least hindered side of the C20 ketone in 21 producing a 90% yield of the single stereoisomer 22. The resulting C17-C27 bryostatins produced in these studies have shown potential anti-cancer properties. 

Other reactions. The deoxygenation of bis(tributyltin)oxide to afford hexabutylditin in EtOH, 2h, 83% yield) and the conversion of Af-alkenylpyridinium salts to ketones are accomplished using NaBH as reagent. Anilines are obtained by reduction of nitroarenes u ith NaBH -fNH l SO. ... 

Polonoeski reaction (2, 7 5, 3). The first synthesis of the dimeric indole alkaloid vinblastine (4), used in the treatment of lymphomas, involved coupling of two indole units using a Polonovski reaction. Thus reaction of the N-oxide (1) and vindoline (2) with trichloroacetic anhydride afforded the quaternary im-monium compound (3), which was converted into (4) by standard methods (reduction with NaBH, rcacclylalion). ... 

Figure 1.5. Synthesis of the spherical polyelectrol3le (left) and cryo-TEM of Pd SPB (right) used for coupling reactions. Long chains of poly[(2-methylpropenyloxyethyl) trimethylam-monium chloride] were grafted onto polystyrene cores of approximately 100 nm diameter. PdCl4 ions were introduced as counterions and reduction hy NaBH in aqueous solution ied to Pd nanoparticles with diameters of 2.6 0.5 nm immobilized on the surface of the carrier particles. (See Ref. 48.)...

Sodium borohydride has been extensively used as a reducing agent. The solid state reduction with NaBH requires longer time and use of solvents slow down the reaction. A microwave irradiation reaction has been developed for the reduction of aldehydes and ketones using alumina supported NaBH (Scheme 23). 

Alternatively, Garter s group has worked on the synthesis of (5)-Af-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarbox-amide ((6)-20) and its use as organocatalyst for the direct Mannich reaction (Scheme 2.5) [22], obtaining the p-amino carbonyl compounds 21 and 22 as well as the y-amino alcohol 23, after a reduction with NaBH. ... 

Dimethylocta-l,6-diene was used as a substrate for the highly -selective hydroformylation with a homogeneous Rh(Xantphos) catalyst (Scheme 6.21) [95]. The odor of the aldehyde yielded was described as fresh, orange peel, and herbaceous with coriander leaf accents. Subsequent reduction with NaBH yielded the unsaturated alcohol, which was characterized from the olfactory point of view as rustic with a note of floral, bergamot, and cinnamon. 

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