Pyridines with 2,4-position alkyl groups have acidic hydrogens on the carbon adjacent to the pyridine ring.

alkyl vinyl quinolines 01

Hydrogens can be subtracted using strong bases. The base formed is a good nucleophile and allows the attack of various carbon electrophiles.

alkyl vinyl quinolines 02

Isoquinoline has acidic hydrogens in position 1.

alkyl vinyl quinolines 03

The delocalization of the charge towards the nitrogen atom is key for the hydrogen to present acidity. The 3-position hydrogens (in isoquinoline) are much less acidic since such delocalization causes the breakdown of aromaticity in the carbocycle.

Quinolines with 2,4-vinyl groups or isoquinolines with 1-vinyl groups are attacked by nucleophiles on the vinyl double bond.