Sodium cyanoborohydride quinoline

In this cyclization reaction, as mentioned above, 3,4-dihydroquino-line 81 is generated as the initial product (Scheme 36). If this 3,4-di-hydroquinoline 81 could be reduced prior to the disproportionation, then 1,2,3,4-tetrahydroquinoIine 83a should be obtained. Accordingly, the cyclization of 80a was attempted in the presence of a reducing reagent, sodium cyanoborohydride (Na[BH3(CN)]), and 2-methyl-l,2,3,4-tetrahydroquinolin-8-ol (83a) was produced in 78% yield without the formation of quinoline 82a (Scheme... 

NBH, in the presence of carboxylic acids. Reduction with sodium cyanoborohydride gives reduction but no alkylation under similar conditions. The reduction of 5-nitroisoquinoline produced dihydroiso-quinoline (27) or tetrahydroisoquinoline (28) with NBH in acetic acid, depending on the solvent and temperatures employed. 

Heald repeated the same reduction of 6-nitroquinoline (147) at a higher temperature and isolated 1-ethyl-l,2-dihydro-6-nitroquinoline (148), the product of reductive alkylation. With quinoline and NBH in carboxylic acids the Aralkyl-1,2,3,4-tetrahydroquinoline 149 is obtained. Use of sodium cyanoborohydride gives reduction but no alkylation (150). In the presence of acetone, l-isopropyl-l,2,3,4-tetrahydroquinoline (151) is the predominant compound. Quinoline W-oxides undergo deoxygenation, and some ring reduction with NBH. ... 

Isoquinoline (176), as in the case of quinoline, undergoes reductive alkylation with NBH in the presence of carboxylic acids, affording the amine 184. Sodium cyanoborohydride under these conditions gave the unalkylated product 177. Under similar conditions, but at lower temperature, 5-ni-troisoquinoline affords the tetrahydroisoquinoline. ... 

Selective reduction of either the pyridine or the benzene rings in quinolines and isoquinoline can be achieved the heterocyclic ring is reduced to the tetrahydro level by sodium cyanoborohydride in acid solution,by sodium borohydride in the presence of nickel(II) chloride, by zinc borohydride," or, traditionally, by room temperature and room pressure catalytic hydrogenation in methanol. However, in strong acid solution it is the benzene ring which is selectively saturated " longer reaction times can then lead to decahydro-derivatives. 

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. 

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