Potassium borohydride pyridinium salts

According to another approach, treatment of A-[2-(indol-3-yl)ethyl]-l,2,5,6-tetrahydropyridine (137), obtained from the corresponding pyridinium salt 136 by borohydride reduction, first with potassium rerf-butoxide, and then with acetic acid, led to ( )-l via key intermediate 135 in 78% yield (102). 

The reduction of 2-substituted-isoquinolinium salts has been reported by Torossian65 with potassium borohydride in water, by Mirza,68 and by Durmand et al.,87,68 using sodium borohydride in aqueous methanol to yield 1,2,3,4-tetrahydroisoquinolines. The reduction of the second double bond appears to arise from a mechanism similar to that leading to tetrahydropyridines from pyridinium ions (see Section I). Mirza66 (see also Bose60) found that the reduction of berberine (60) with sodium borohydride could be stopped at the 1,2-dihydro-intermediate (61), and Karrer and Brook70 showed that the 1,2-dihydroisoquinoline formed by the lithium aluminum hydride reduction of l-phenyl-2-methylisoquinolinium iodide (62) could be further reduced to the 1,2,3,4-tetrahydroisoquinoline (63) with sodium borohydride in methanol. Awe et al.71,72 and Huffman73... 

Reductions of quaternary pyridinium salts to 1-alkyl-3-piperideines may be performed preferably with the use of sodium or potassium borohydride in aqueous or alcoholic solutions. Lithium aluminum... 

Sodium and potassium borohydrides are above all used for reducing aldehydes and ketones (Sections 3.2.1, 3.2.2) a,p-ethylenic ketones are converted to mixtures [W3]. In alcoholic media or THF, they leave epoxides, esters and lactones, acids, amides, and most nitro compounds unreacted, but they reduce halides (Section 2.1), anhydrides (Section 3.2.6), quartemary pyridinium salts (Section 3.3), double bonds conjugated to two electron-withdrawing groups (Sections 3.2.9, 4.4), and CUPd... 

---

See also in sourсe #XX -- [ ]

---