NaBH4, reduction

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

TABLE 2-2 NaBH4 Reduction of Steroids, Epimers Formed (% or Ratio)... 

When the C/D ring fusion is cis, the 17a-hydroxy compound is the main product from NaBH4 reductions of l7-keto-13a-androst-5-en-3)9-oE or 14/ -H compounds. The absence of a 10-methyl also affects the course of the reaction when rings A and B are cw-fused. A 19-nor-5/ -H 3-ketone is reduced to the 3/ -isomer, as is a 10a-H-5a-H-19-nor-3-keto compound. ... 

With one exception, NaBH4 reduction of the 20-ketone gives the 20/ -alco-hol as the major product even with substitution patterns where LiAlH4 gives the The exception is the... 

Definitive identification of lysine as the modified active-site residue has come from radioisotope-labeling studies. NaBH4 reduction of the aldolase Schiff base intermediate formed from C-labeled dihydroxyacetone-P yields an enzyme covalently labeled with C. Acid hydrolysis of the inactivated enzyme liberates a novel C-labeled amino acid, N -dihydroxypropyl-L-lysine. This is the product anticipated from reduction of the Schiff base formed between a lysine residue and the C-labeled dihydroxy-acetone-P. (The phosphate group is lost during acid hydrolysis of the inactivated enzyme.) The use of C labeling in a case such as this facilitates the separation and identification of the telltale amino acid. 

Fig. 6.3.11 Chromatography of an extract of the eye light organs of Symplecto-teuthis luminosa on a column of Superdex 200 Prep (1x27.5 cm) in 20 mM phosphate buffer, pH 6.0, containing 0.6 M NaCl, at 0°C (monitored at 280 nm). Each fraction (0.5 ml) is measured for the initial intensity of H202/catalase-triggered luminescence and the content of dehydrocoelenterazine measured as coelenterazine after NaBH4-reduction 1LU = 6 x 108 photons.

Becker et al., (1984) investigated the photo-CIDNP effect in the presence of crown ethers (see Sec. 11.2). CIDNP studies on the photolysis (Jiang et al., 1990) and on the NaBH4 reduction (Song et al., 1990) of arenediazonium ions showed that free radical intermediates are involved. 

Wunberg, J.B.P.A. Speckamp, W.N. (1978) New Total Synthesis of dl-Physostigmine (dl-Eserine) Via Regioselective NaBH4-reduction of Imides. Tetrahedron, 34, 2399-2404. 

Other one-pot preparations of bimetallic nanoparticles include NOct4(BHEt3) reduction of platinum and ruthenium chlorides to provide Pto.sRuo.s nanoparticles by Bonnemann et al. [65-67] sonochemical reduction of gold and palladium ions to provide AuPd nanoparticles by Mizukoshi et al. [68,69] and NaBH4 reduction of dend-rimer—PtCl4 and -PtCl " complexes to provide dend-rimer-stabilized PdPt nanoparticles by Crooks et al. [70]. 

Ag-core/Au-shell bimetallic nanoparticles were prepared by NaBH4 reduction method [124]. UV-Vis spectra were recorded and compared with various ratios of AuAg alloy nanoparticles. The UV-Vis spectra of bimetallic nanoparticles suggested the formation of core/shell structure. Furthermore, the high-resolution transmission electron microscopy (HRTEM) image of the nanoparticles confirmed the core/shell type configuration directly. 

Bimetallic Ag-core/Au-shell nanoparticles, prepared by a NaBH4 reduction method, were directly confirmed by HRTEM [124],... 

Oxymercuration of 4-f-butylcyclohexene, followed by NaBH4 reduction, gives czT-4-f-butylcyclohexanol and frans-3-f-butylcyclohexanol in approximately equal amounts. l-Methyl-4-f-butylcyclohexanol under similar conditions gives only czT-4-f-butyl-l-methylcyclohexanol. Formulate an explanation for these observations. 

The data below give the ratio of equatoriahaxial alcohol by NaBH4 reduction of each cyclohexanone derivative under conditions in which 4-r-butylcyclohexanone gives an approximately 85 15 ratio. Analyze the effect of the substituents in each case. 

The key cyclization in Step B-2 was followed by a sequence of steps that effected a ring expansion via a carbene addition and cyclopropyl halide solvolysis. The products of Steps E and F are interesting in that the tricyclic structures are largely converted to tetracyclic derivatives by intramolecular aldol reactions. The extraneous bond was broken in Step G. First a diol was formed by NaBH4 reduction and this was converted via the lithium alkoxide to a monomesylate. The resulting (3-hydroxy mesylate is capable of a concerted fragmentation, which occurred on treatment with potassium f-butoxide. 

Activation of a primary alcohol 174 by in situ mesylation and nucleophilic attack of a pyridine nitrogen atom was used in the last steps of a synthesis of cyclohexa[tf]quinolizidines 176. These compounds were obtained by direct NaBH4 reduction of intermediate pyridinium salts 175, and were proposed as tricyclic models containing the ABC-part of 8-azasteroids (Scheme 30) <1999T9269>. 

NaBH4 reductions can be carried out in water or alcohol solutions. 

The practical applications of NaBH4 reductions on mineral surfaces for in situ generated SchifFs bases have been successfully demonstrated. The solid-state reductive amination of carbonyl compounds on various inorganic solid supports such as alumina, clay, silica etc. and especially on K 10 clay surface rapidly afford secondary and tertiary amines [126]. Clay behaves as a Lewis acid and also provides water from its interlayers thus enhancing the reducing ability of NaBH4 [22],... 

Figure 5.19. Schematic design of the NaBH4-reduction/flame photometric detection system for the determination of tin species in natural waters. Source Author s own files...

Figure 5.20. a Chromatogram of stibine, methylstibine, and dimethylstibine as separated by the OV-3 trap/column with the quartz furnace/AA detector. The stibines were prepared by the NaBH4 reduction of 2 ng Sb each as Sb (III), methylstibonic, and dimethylstibonic acid, b Analysis of a sample of seawater (100 ml) from the open Gulf of Mexico (Station SN4-3-1, 12 March 1981)... 

The 7-hydroxy-a,/3-( )-alkenoic esters were prepared readily from acid halides and silver acetylenides followed by NaBH4 reduction (Table 7).515... 

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