Pyridine reductions with

Reduction. Quinoline may be reduced rather selectively, depending on the reaction conditions. Raney nickel at 70—100°C and 6—7 MPa (60—70 atm) results in a 70% yield of 1,2,3,4-tetrahydroquinoline (32). Temperatures of 210—270°C produce only a slightly lower yield of decahydroquinoline [2051-28-7]. Catalytic reduction with platinum oxide in strongly acidic solution at ambient temperature and moderate pressure also gives a 70% yield of 5,6,7,8-tetrahydroquinoline [10500-57-9] (33). Further reduction of this material with sodium—ethanol produces 90% of /ra/ j -decahydroquinoline [767-92-0] (34). Reductions of the quinoline heterocycHc ring accompanied by alkylation have been reported (35). Yields vary widely sodium borohydride—acetic acid gives 17% of l,2,3,4-tetrahydro-l-(trifluoromethyl)quinoline [57928-03-7] and 79% of 1,2,3,4-tetrahydro-l-isopropylquinoline [21863-25-2]. This latter compound is obtained in the presence of acetone the use of cyanoborohydride reduces the pyridine ring without alkylation. 

An aiyl methane- or toluenesulfonate ester is stable to reduction with lithium aluminum hydride, to the acidic conditions used for nitration of an aromatic ring (HNO3/HOAC), and to the high temperatures (200-250°) of an Ullman reaction. Aiyl sulfonate esters, formed by reaction of a phenol with a sulfonyl chloride in pyridine or aqueous sodium hydroxide, are cleaved by warming in aqueous sodium hydroxide. ... 

The 1,2-dihydro derivative is formed by reduction of pyridine with LiAlH4 (85). Analogous reduction with sodium in 95 % alcohol affords the 1,4-dihydro derivative. Monomeric N-trimethylsilyl-l,2,3,4-tetrahydro (28)... 

Treatment of 3-phenylperhydro[l, 3]oxazolo[3,2-a]pyridine-5-carboxylates 303 and 304 with BF3 Et20 in THE, followed by reduction with NaBD4 afforded 6-deutero-4-phenylperhydropyrido[2,1 -c][l, 4]oxazin-1 -ones 220 and 222 (97JA6446). 

A more general route to 4-acetoxy-l,3-dioxanes utilizes the reductive acylation of l,3-dioxane-4-ones [46] (Scheme 21). l,3-Dioxane-4-ones 126 are prepared from the corresponding -hydroxy carboxylic acids. Low temperature reduction with DIBALH generates a diisobutylaluminum hemiacetal (127) which undergoes acylation in situ with AC2O in the presence of pyridine and DMAP. This method allows for the preparation of a wide range of 4-acetoxy-l,3-dioxanes, without the problem of a-epimerization. This method also represents a general approach to acylic a-acetoxy ethers, which are themselves useful synthetic intermediates [47,48]. 

We have previously (13) reported a rapid two step synthesis of 4-(pyrrolidino)pyridine copolymers via the reaction of commercially available maleic anhydride copolymers with 4-aminopyridine followed by reduction with LiAlH, yielding polymers with a high degree of functionalization. 

However, the reaction always led to some overreduction of the pyridine ring. Reduction with BH /THF was unsuccessful. However, NaBH /BF2 Et20 proved to be an excellent reagent for the reduction step, resulting in the formation of the desired polymer. The polymer was shown by UV and NMR spectroscopy to be 67% functionalized primarily with 4-pyrrolidinopyridine moieties by UV and NMR spectroscopy according to these data no starting polymer is present anymore, and the nature of the remaining 23% of functionalization is unknown. 

The reduction of nitrobenzene may also be accomplished by triplet excited pyrochlorophyll Comparison of the quantum 5delds of such photoreductions by hydrazobenzene in ethanol-pyridine solutions with the polarographic quarter... 

Moderate to good enantioselectivities were obtained for nearly all examples, but the products from 83a-c could be recrystallized to higher enantiomeric purity. Addition of iodine was critical for catalysis as was the use of a ligand with electron-poor para-fluorophenyl groups on the phosphorous atom. Substitution at the 3 position of the pyridine ring was described as being difficult for both the quinolines and pyridine systems. The resulting hydrazine derivatives could be easily converted to piperdines by reduction with Raney nickel or under Birch conditions. 

The pyridine ring is easily reduced in the form of its quaternary salts to give hexahydro derivatives by catalytic hydrogenation [446], and to tetrahydro and hexahydro derivatives by reduction with alane aluminum hydride) [447], sodium aluminum hydride [448], sodium bis 2-methoxyethoxy)aluminum hydride [448], sodium borohydride [447], potassium borohydride [449], sodium in ethanol [444, 450], and formic acid [318]. Reductions with hydrides give predominantly 1,2,5,6-tetrahydro derivatives while electroreduction and reduction with formic acid give more hexahydro derivatives [451,452]. 

Ketones are obtained from a-diketones by reduction with hydrogen sulfide in a pyridine-methanol solution [237], by refluxing with 47% hydriodic acid in acetic acid (yield 80%) [916], and by decomposition of monohydrazones with alkali [923]. Reduction of a-diketones to hydrocarbons is achieved by decomposition of bis-hydrazones by alkali [923]. 

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