Isoquinoline reduction with sodium hydride

The reduction of quinoline with either lithium or sodium in liquid ammonia produces only 1,4-dihydroquinoline . Formation of 1,2-dihydroisoquinolines was observed in the reduction of quaternary isoquinoline salts with sodium hydrosulphite ", lithium aluminium hydride " , NaBH4 , dialkylaluminohydrides or on treatment with a Grignard reagent . 

Reduction of norcoralyne with zinc and acetic/hydrochloric acid yields dihy-dronorcoralynium chloride, which can be oxidized by m-chloroperbenzoic acid to the betaine (92), photolysis of which (followed by reduction with sodium boro-hydride) yields the phthalide-isoquinoline (93), obtainable from 2 -acetyl-papaveraldine. ... 

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

Cyclic enamines can also be obtained by the reduction of pyridine and isoquinoline with lithium aluminum hydride (163-165), and the latter reduction has also been accomplished with sodium in liquid ammonia (166). 

Thiazoles are deactivated towards electrophilic substitution, and thus direct reaction with hydride re-ductants to give thiazolines should be facilitated. There are indeed some examples of this type of reaction, but it is more common to reduce N-alkylated thiazolium salts (209). These compounds are converted first by reaction with sodium borohydride into 4-thiazolines (210), which in protic solvents become protonated and undergo further reduction to yield thiazolidines (211). Similarly the isoquinoli-nium salt (213), formed by the acid-promoted cyclization of the isoquinoline (212), is converted into the tetrahydroisoquinoline (214) (presumably via an intermediate 1,2-dihydroisoquinoline) by reaction with sodium borohydride. ... 

When treated with diethylaluminium hydride, isoquinoline yields its 1,2-dihydro derivative, as does quinoline. Metal reductions, e.g. with sodium in liquid NH3 or with tin/HCl, afford the tetrahydroisoquinoline 26. Isoquinolinium ions are reduced to 1,2,3,4-tetrahydroisoquinolines by NaBH4. This reaction is important for establishing the structure of alkaloids. Since the reduction of the... 

The synthesis of 8-aza-D-homoestrogens has also been carried out from compound (432) (Scheme 42) [551, 552]. Compound (432) was converted via (435) in four stages into the isoquinoline derivative (438). The action of thionyl chloride led to the chloride (439), which, on reaction with 2,4-dim ethoxy-.1,4-cyclohexadiene, gave the tricyclic compound (440). Acid hydrolysis of this compound was accompanied by cyclization to the D-homo derivative (443). Reduction of the latter with lithium aluminum hydride gave a mixture of equal amounts of the cis-C/D ketone (441) and the trans-C/D ketone (442) the first was isomerized into the second on treatment with sodium methoxide. The configuration of compounds (441)-(443) at Cg has remained undetermined. 

Hydroisoquinolines. In addition to the ring-closure reactions previously cited, a variety of reduction methods are available for the synthesis of these important ring systems. Lithium aluminum hydride or sodium in Hquid ammonia convert isoquinoline to 1,2-dihydroisoquinoline (175). Further reduction of this intermediate or reduction of isoquinoline with tin and hydrochloric acid, sodium and alcohol, or catalyticaHy using platinum produces... 

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