1- Cyanopyridinium bromide

Bromocyanogen and pyridine give 1-cyanopyridinium bromide, important for ring-opening reactions (see e.g. Section 3.2.1.6.3.iv). 

Labelled cyanogen bromide ( CNBr) has been used by Westerberg and Langstrom to synthesize several aromatic cyanates, and cyanamides, a 1-cyanopyridinium bromide and phenyl and benzyl thiocyanates in good yields in a few minutes (Scheme 5). The yields for each reaction are in the parentheses. 

Konig found pyridine to give, with cyanogen bromide and arylamines, glutacondialdehyde dianils and cyanamide. The reaction clearly involved the 1-cyanopyridinium ion. Alkylamines can be used in an interesting variation 200 diethylamine hydroperchlorate converts 1-cyanopyridinium bromide into (143). Some substituted pyridines can be used in the reaction ... 

Reduction of A-benzyl-3-cyanopyridinium bromide with sodium borohydride in aqueous solution containing -sodium carbonate gave a mixture of the yellow 1,2-dihydropyridine and colorless 1,6-dihydro-pyridine which was condensed with methyl vinyl ketone without purification to furnish the desired isoquinuclidine (XII) in 16% yield. Hydrolysis of the nitrile with cold concentrated hydrochloric acid afforded the amide identical with the adduct prepared by the reduction of l-benzyl-3-carboxamidopyridinium chloride followed by condensation of the crude mixture of reduced pyridines with methyl vinyl ketone. Reduction of the ketoamide with sodium borohydride gave a mixture of epimeric alcohols (XIII) which with sodium hypochlorite in methanol yielded one of the tricyclic urethanes (XIV) in a readily crystallizable... 

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