Quinolines borohydrides

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. 

A solution of N-(2-aminobenzvl)-1-phenyl-2-metKylaminoethanol-1 was prepared by the reaction of a-bromo-acetophenone and (2-nitrobenzyl)methylamine, followed by hydrogenation of the nitro group by means of nickei on diatomaceous earth at room temperature and reduction of the CO group by means of sodium borohydride. The intermediate thus produced was dissolved in 100 ml of methylene chloride and introduced dropwise into 125 ml of sulfuric acid at 10° to 15°C. After a short standing, the reaction mixture was poured onto ice and rendered alkaline by means of a sodium hydroxide solution. Dy extraction with ether, there was obtained 1,2,3,4-tetrahydro-2-methyl-4-phenyl-8-amino-iso-quinoline. The base is reacted with maleic acid to give the maleate melting point of the maleate 199° to 201°C (from ethanol). 

Replacing the metal Al by a boron atom as the metal chelate center, Tao et al. reported lithium tetra-(2-methyl-8-hydroxy-quinolinato) boron (LiB(qm)4, 240) (Scheme 3.73) quantitatively prepared by reaction of lithium borohydride (LiBH4) with four equivalents of 2-methyl-8-hydroxy-quinoline in ethanol at room temperature [266]. LiB(qm)4 is a pure blue emitter with a maximum peak emission at 470 nm with FWHM of 75 nm. Devices of... 

Palladium catalysts are more often modified for special selectivities than platinum catalysts. Palladium prepared by reduction of palladium chloride with sodium borohydride Procedure 4, p. 205) is suitable for the reduction of unsaturated aldehydes to saturated aldehydes [i7]. Palladimn on barium sulfate deactivated with sulfur compounds, most frequently the so-called quinoline-5 obtained by boiling quinoline with sulfur [34], is suitable for the Rosenmund reduction [i5] (p. 144). Palladium on calcium carbonate deactivated by lead acetate Lindlar s catalyst) is used for partial hydrogenation of acetylenes to cw-alkenes [36] (p. 44). 

Reduction of quinoline with lithium aluminum hydride gives 1,2-dihydroquinoline. Neutral pyridines bearing electron-withdrawing substituents are also reduced by sodium borohydride (Scheme 32). 

Different hydrogenolytic reactivity of trifluoromethyl groups with respect to their position on the quinoline ring is observed. All C-F bonds in 2-, 4- and 6-(trifluoromethyl)quinoline are hydrogenolyzed by lithium aluminum hydride (Table 4), but the 3-trifluoromethyl isomer gave 3-(difluoromethyl)-l,2-dihydroquinoline (10) under the same experimental conditions in contrast to these results, sodium borohydride surprisingly reduces 3-(trifluoromethyl)quinoline to the corresponding 3-methylquinoline (Table 4).149... 

Numerous reducing agents were tried at this point unsuccessfully. For example, lithium aluminum hydride destroyed the substrate, whereas DIBAH or lithium borohydnde in THF and sodium borohydride in ethanol led to reduction of the quinoline system. On the other hand, both potassium borohydride (either with or without 18-crown-6) and zinc borohydride (with or without ethanol) produced no reaction at all. Lithium triethylborohydride resulted in de-methoxylation, and sodium borohydride in refluxing THF gave a 45% yield of diol 16 together with overreduced product. 

Consequently, Dehmlow and coworkers modified the cinchona alkaloid structure to elucidate the role of each ofthe structural motifs of cinchona alkaloid-derived chiral phase-transfer catalysts in asymmetric reactions. Thus, the quinoline nucleus of cinchona alkaloid was replaced with various simple or sterically bulky substituents, and the resulting catalysts were screened in asymmetric reactions (Scheme 7.2). The initial results using catalysts 8-11 in the asymmetric borohydride reduction of pivalophenone, the hydroxylation of 2-ethyl-l-tetralone and the alkylation of SchifF s base each exhibited lower enantiomeric excesses than the corresponding cinchona alkaloid-derived chiral phase-transfer catalysts [14]. 

Reduction is commonly employed to convert imino and oxo bisbenzyliso-quinoline alkaloids to identifiable derivatives, or to other alkaloids. Thus thalsimine (58) gave, with either Zn/H2S04 or NaBH4, a mixture of norheman-dezine (234) and its epimer (391) (81). Sodium borohydride reduction of thalictrinine (Section II,C,114) gave specifically dihydrothalictrinine (Section II,C,31), from attack at the less hindered side of the carbonyl (81). 

The reduction of isoquinolinium ions has been extensively investigated with borohydride and aluminum hydride ions. The use of boro-hydride ion in a protonic solvent normally leads to the formation of 1,2,3,4-tetrahydroisoquinolines, whereas the reduction with aluminum hydride ion in an aprotic medium generally gives a 1,2-dihydroiso-quinoline. This 1,2-dihydroisoquinoline contains an enamine system and may undergo further reaction on treatment with acid. The 1,2-and 3,4-dihydroisoquinolines as well as isoquinolinium ions are reduced by the borohydride ion in a protonic medium to the 1,2,3,4-tetrahydroisoquinolines. 

As would be expected, the weaker reducing agent, sodium boro-hydride, has received little attention for the reduction of quinolines. The reaction of 2-chloro-3,7-dicarbomethoxy-5,6-benzoquinoline (80) has been reported by Walker to yield 3,7-dicarbomethoxy-5,6-benzo-1,4-dihydroquinoline (81) on reaction with sodium borohydride.96 The success of this reaction may depend upon the electron-withdrawing properties of the carbomethoxy groups. 

Bis[2-(quinolin-2 -yl)phenyl] Tritellurium4 To a suspension of 2.28 g (4.0 mmol) 2-(quinolin-2 -yl)phenyl tellurium tribromide in 25 ml ethanol are added 0.26 g (4 mmol) tellurium powder. The mixture is stirred under argon. A solution of 1.1 g (30 mmol) sodium borohydride in 20 ml ethanol is slowly added until all the... 

Disodium telluride, prepared from tellurium and sodium borohydride, and 2-chloro-3-(2-chloroethyl)quinoline formed 2,3-dihydroquinolo[3,2-d]tellurophene3. 

Dihydroquinolo[2,3-rf] tellurophene (Sodium Borohydride Method)3 A mixture of 2.55 g (1 mmol) of 2-chloro-3-(2 -chloroethyl)-quinoline, 0.127 g (1 mmol) of tellurium, and 0.20 g (5.3 mmol) of sodium borohydride in ethanol is heated on a steam bath under reflux in nitrogen for 6 h. The mixture is then concentrated, poured into ice-cold water, and extracted with chloroform. The extract is dried with anhydrous sodium sulfate, filtered, and evaporated. The oily residue is chromatographed on silica gel with benzene as the mobile phase. The yellow fractions are collected, the benzene is evaporated, and the residue is recrystallized from benzene/petroleum ether (b.p. 60-80°) yield 0.1 g (35%) m.p. 123°. 

Deuteration of Quinoline and Isoquinoline with Borohydride-Reduced Catalysts0... 

The 2-, 3-, 4-, and 6-trifluoromethyl derivatives of quinoline on treatment with LAH give a variety of products that depend on the position of the substituent. Only the 3 isomer 152 leads to anything other than dehalogena-tion, giving 3-(difluoromethyl)-l,2-dihydroquinoline (153). On the other hand, with sodium borohydride, only 152 undergoes complete dehalogena-tion (154). This is believed to proceed via ring attack and the involvement of a 1,4-dihydroquinoline (155). 

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