Quinolinium salts borohydrides

A. Reductions with Sodium Borohydride Quinolinium salts are converted by sodium borohydride to the corresponding 1,2,3,4-tetrahydroquinolines as the major product. Usually, however, small amounts of 1,2-dihydroquinoline can be... 

However, l-benzyl-3-cyanoquinolinium bromide (168) gives a 75% yield of the 1,4-dihydro adduct 169 when reduced with NBH and allowed to equilibrate in the presence of the parent quinolinium salt. 1,4-Dimethyl-2-methylaminoquinolinium iodide (170) undergoes hydride attack at the 2 position with borohydride to give the product 171 as an unstable yellow oil. Alstonilin or benz[ ]indolo[2,3-fl]chinolizidine-type alkaloids (173) have been successfully prepared in high yields from the isoquinolinium salt 172 via hydride reduction. ... 

The key intermediate 21 is in principle accessible in any of several ways. Thus reaction of thiophenecarbox-aldehyde with amninoacetal would lead to the Schiff base 20 treatment with acid would result in formation of the fused thiophene-pyridine ring (21). Alkylation of that intermediate with benzyl chloride gives the corresponding ternary imini urn salt 23. Treatment with sodium borohydride leads to reduction of the quinolinium ring and thus formation of ticlopidine (24). ... 

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