Potassium phthalimide reacts with 'A' which on hydrolysis gives isopentylamine, what is 'A'?

Potassium phthalimide on reaction with compound (A) followed by hydrolysis forms isopentyl amine. The compound (A) will be:

N - methyl phthalimide on hydrolysis gives :

N - methyl phthalimide on hydrolysis gives :

Potassium reacting with cold water

Acetaldehyde reacts with CH_3MgBr and the product on hydrolysis gives