Sodium dithionite pyridines

The Zincke reaction has also been adapted for the solid phase. Dupas et al. prepared NADH-model precursors 58, immobilized on silica, by reaction of bound amino functions 57 with Zincke salt 8 (Scheme 8.4.19) for subsequent reduction to the 1,4-dihydropyridines with sodium dithionite. Earlier, Ise and co-workers utilized the Zincke reaction to prepare catalytic polyelectrolytes, starting from poly(4-vinylpyridine). Formation of Zincke salts at pyridine positions within the polymer was achieved by reaction with 2,4-dinitrochlorobenzene, and these sites were then functionalized with various amines. The resulting polymers showed catalytic activity in ester hydrolysis. ... 

An intriguing use of a quaternary ammonium salt in a two-phase reaction is to be found with the regeneration of 1 -benzyl-1,4-dihydronicotinamide by sodium dithionite in a biomimetic reduction of thiones to thiols [12], The use of sodium dithionite in the presence of sodium carbonate for the 1,4-reduction of the pyri-dinium salts to 1,4-dihydropyridines is well established but, as both the dithionite and the pyridinium salts are soluble in water and the dihydropyridine and the thione are insoluble in the aqueous phase and totally soluble in the organic phase, it is difficult to identify the role of the quaternary ammonium salt in the reduction cycle. It is clear, however, that in the presence of benzyltriethylammonium chloride, the pyridine system is involved in as many as ten reduction cycles during the complete conversion of the thione into the thiol. In the absence of the catalyst, the thione is recovered quantitatively from the reaction mixture. As yet, the procedure does not appear to have any synthetic utility. 

Aminopyrrolopyridines are available by reduction of the corresponding nitro compounds (Section 3.09.3.2.3) or azo dyes (Section 3.09.3.2.6). 3-Nitro-2-phenylpyrroIo[2,3-6]pyridine is reduced by sodium dithionite to an unstable 3-amino derivative (71). It is... 

Warburg and Christian recognized the relationship of NADP+ and NAD+ (then called DPN+) and proposed that both of these compounds act as hydrogen carriers through alternate reduction and oxidation of the pyridine ring. They showed that the coenzymes could be reduced either enzymatically or with sodium dithionite Na2S204. 

The purity of the hemin ester can be checked by tic (silica gel, with CHC13/ methanol = 5 1), or by visible spectroscopy. A small amount of the hemin ester dissolved in pyridine can be reduced by sodium dithionite in a cuvette.1 2 The resultant hemochrome should exhibit two absorption maxima at 557 and 526 nm. If necessary, the product can be further purified by chromatography on an alumina (grade III) column (1X10 cm) using a mixture of chloroform and methanol (10 1) as eluent. However, the iron prophyrin compound obtained after chromatography exists as the p-oxo dimer, [Fe(III)-O-Fe(III)], which may be converted back to the chloride by treatment in CHC13 with dry HO followed by crystallization from chloroform/methanol. 

Mesohemin IX prepared by this method shows a single band on polyamide tic (benzene/methanol/formic acid, 110 15 1 and methanol/acetic acid 100 2)10 and on silica gel tic14 (benzene/methanol/formic add, 110 30 1). The electronic spectrum of the pyridine hemochrome, prepared by reducing the mesohemin (in pyridine) with an aqueous solution of sodium dithionite, contains the bands (4 N pyridine, 0.2 N KOH) Xmax 407.5, 516, 546.2 nm. e 139.5,20.9,35.8 (mAT1). 

Examples of seven-coordination in pyridine-containing macrocycles have also been osberved. Thus the iron(TI) complexes [Fe(L)X,] xhLO (L = 126 X = halide or pseudohalide) are formed923 when the corresponding seven-coordinate iron(lll) complexes are reduced with aqueous sodium dithionite in the presence of excess NaX or by the direct template synthesis with 2,6-diacetylpyridine and the corresponding tetramine in the presence of iron(IJ). The triimine moiety gives rise to a strong... 

Finally, mention must be made of the nicotinamide nucleosides. Fischer and Raske observed the quaternization of tetra-O-acetyl-a-D-glucopyranosyl bromide with pyridine, and Karrer and coworkers extended this reaction to the synthesis of quaternary, nicotinamide nucleosides. The condensation has been improved by Haynes and Todd, who used acetonitrile as solvent. With tri-O-acetyl-a-D-ribofuranosyl bromide, D-ribofuranosylnicotinamide—a structural unit of coenzyme I (DPN)—was obtained, and this was reduced with sodium dithionite to the dihydro derivative. 

Derivatives of 1,4-dihydronicotinamide (2) and l,4-dihydropyridine-3,5-dicarboxylic acid (8) are obtained from the corresponding pyridines by alkylation followed by reduction with sodium dithionite, as illustrated for (76) in equation (33). The absolutely regioselective reduction by dithionite of pyridinium salts to 1,4-dihydropyridines is true synthetic good fortune most other reducing agents reduce pyridinium salts nonregioselectively and often with reduction beyond the dihydro stage. 

Few truly catalytic systems have been reported. An V-alkylated 1,4-dihydropyridine forms a pyridin-ium salt on hydride loss. In principle the pyridinium salt may be recovered and reduced regioselectively with sodium dithionite (equation 33). This reaction is veiy general and fails only when the 1,4-dihydro-pyridines are excessively strained or too reactive to be isolated. 

Mn11 porphyrins are obtained in solution by reduction of Mnm complexes with sodium dithionite in the presence of pyridine [Calvin (23), Loach (124)], or in the solid state as a thin layer by evaporation of Mn111 porphyrins in high vacuum [Calvin (22), Edwards (52)]. No preparation of crystalline materials has been reported so far. 

Reductive cyciization occurs when an r>-acylsulphonamide is treated with sodium dithionite in pyridine. 

A mixture of 1,4-anthraquinone and pyridine containing a little 1,4-anthrahydro-quinone (prepared by shaking 1,4-anthraquinone with aq. 6% sodium dithionite soln. in ether) stored 40 hrs. at room temp, under Ng cyclotri-l,4-anthra-quinone. Y 81%. H. Brockmann and H. Laatsch, B. 106, 2058 (1973). 

The iron(III) complex, [FeL2l , (L2- = pyridine-2,6-dicarbothioate) is reduced 5 jn aqueous solution by sodium dithionite with formation of the dianionic iron(II) complex, [FeL2]2-. Wade and Castro have reported the synthesis of [Fe(tpp-d)] by reduction of the iron(III) compound, [FeCl(tpp-d)] with Na2S204 in an alkaline aqueous-isopropanol medium. Reduction of sodium nitroprusside, Na[Fe(CN)5(N0)]-2H20, with sodium dithionite, followed by addition of 2,2 -bipyridyl and tetraphenylphosphonium bromide, yields a precipitate of [Ph4P][Fe(CN)3(NO)(bipy)].57... 

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