Sodium dithionite, reduction

After its isolation, the structure of alkaloid deplancheine (7) was unambiguously proved by several total syntheses. In one of the first approaches (14), 1,4-dihydropyridine derivative 161, obtained by sodium dithionite reduction of A-[2-(indol-3-yl)ethyl]pyridinium salt 160, was cyclized in acidic medium to yield quinolizidine derivative 162. Upon refluxing 162 with hydrochloric acid, hydrolysis and decarboxylation took place. In the final step of the synthesis, the conjugated iminium salt 163 was selectively reduced to racemic deplancheine. 

One of the oldest-known reactions of N-nitrosamines is their reduction to 1,1-disubstituted hydrazines discovered by Fischer (19) The most common method to perform this transformation has been zinc dust in acid, generally acetic acid tetrazenes are sometimes formed as by-products (20) and denitrosation can also occur. Several other reducing methods have been investigated reduction with lithium aluminum hydride and catalytic hydrogenation are sometimes useful. Sodium dithionite reduction of benzyl substituted N-nitrosamines in base can result in fragmentation to... 

Ethoxycarbonyl-l,2,3,4-tetrahydroquinoxalin-2-ones (86) are obtained either by sodium dithionite reduction of the corresponding quin-oxalinone esters or by direct synthesis from o-phenylenediamines and bromomalonic ester (85).102... 

Sodium dithionite reduction of pyridinium salts, usually substituted with electron-withdrawing groups in the 3- or 3,5-positions, chiefly affords the corresponding 1,4-dihydropyridines. The regioselectivity of formation of the dithionite adducts and mechanisms of decomposition have been studied <2005T10331, 2000TL1235>. The sodium... 

Karrer20 has reported the isolation of a dihydro-p-phenanthroline from the sodium borohydride reduction of p-phenanthroline meth-iodide (26). An isomeric dihydro-p-phenanthroline was isolated from the sodium dithionite reduction of this methiodide. The isomeric dihydro-p-phenanthrolines were found to give the same tetrahydro-p-phenanthroline on catalytic hydrogenation. On heating, the isomer obtained from the borohydride reduction was found to undergo a facile conversion to the dihydro-p-phenanthroline obtained from the dithionite reduction. 

The preparation of /in-benzoinosine-4,9-quinone (168) was carried out by regioselective ribo-sylation of 4-nitroimidazo[4,5- ]quinazolin-8(3//,7//)-one followed by nitro group reduction, Fremy oxidation, and deacetylation <9lJOC776>. 4-Amino-//n-benzohypoxanthine (169 R = H) was prepared (80%) by sodium dithionite reduction of 5-nitroimidazo[4,5-.9]quinazolin-8(3//,7//)-one, but... 

Sodium dithionite reduction, sodium citrate chelation, determination by atomic absorption spectrometry 23,24, ... 

Sodium dithionite reduction of [(McgCg)2Fe] gave the paramagnetic Fe(I) cation [(MegCg)2Fe] 149). Electron spin resonance studies have... 

Na2s2°. (Sodium dithionite) Reduction of ArN02 Penetrating odor of reagent and by-products... 

Lounasmaa et al. ° have continued their investigations into the synthesis of indoloquinolizidine derivatives, with particular reference to vallesiachotamine models. The most advanced work in this area to date involves synthesis (Scheme 9) of the closely related vallesiachotamine derivative (75). The critical stage in this synthesis was the reduction of the pyridinium salt (76) by means of sodium dithionite, which, in buffered (NaHC03) solution, allowed the isolation of the dihydropyridine derivative (77). Cyclization of (77) in the presence of acid gave, preferentially, the desired 3H,15H-trans-isomer (75), as had previously been established " in model systems. Alternatively, alkylation of the unsaturated ester (78) with tryptophyl bromide gave the pyridinium salt (79), which, on reduction with sodium dithionite in aqueous methanol, gave a mixture of (75) and the uncyclized tetrahydropyridine derivative (80). >yhen the sodium dithionite reduction medium was buffered (with NaHCOa), and the dihydropyridines so obtained were cyclized in acid, the products were the tetracyclic geometrical isomers of structure (81) (Scheme 9). 

Sodium dithionite reduction of 1-hydroxy- or aminoanthraquinones to their leuco-forms, followed by condensation with aldehydes to yield the 2-alkylated anthraquinones. 2-Hydroxyanthraquinones yield 1-alkylated products ... 

Intermediates in the sodium dithionite reduction of pyridinium salts have been isolated. Thus l-(p-chlorobenzyl)nicotinamide (X-129) yielded the dihydrosulfmate X-130, which is desulfmated in alkaline media to l-(p-chlorobenzyl)-l,4-dihydronicotinaniide (X-131). The desulHnation of X-130 was confirmed by deuterium exchange experiments. 

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