Your son wants interaction because you're the two people in the world that he cares most about. It is often boring playing on his own, and he isn't getting as much positive feedback by himself — he doesn't know if the thing he's done is worthwhile.
There is no silver bullet to address anything with children because every child is different, and every child differs moment to moment. Something that works today may not work tomorrow.
I have personally had the most success with my children by playing with them for a while and giving them guidance that lets them decide on an immediate goal. Build a small building with blocks, then suggest they could improve on it. Sort ponies by size and then suggest they could be sorted by colour. Something that shows you doing a thing, and then a prompt that allows them to follow directions. Once you've given the direction, tell your child that you're going to go do something else: "I'm going to go start dinner now; you see if you can figure this out while I'm over there."
Your child will be engaged for at least as long as it takes you to get to the kitchen, and then one of two things is likely to happen.
- Your child gives up and comes to find you.
- In this case, you may have given a challenge that seems too daunting. Ask for a smaller victory: "Okay, start by finding me a red block!" Off they'll run, then come back with a red (or blue, oops) block. Praise them, and suggest a next step. Something that doesn't require your hands and something that they can do.
- Your child succeeds at the task after some time and comes to ask for your approval on their success.
- If you're right in the middle of draining a pot of boiling spaghetti, ask for a bit of patience. Go see their success as soon as you possibly can, praise it, suggest a change or another task.
There are times when it'll feel like they're interrupting, but just remember that patience and manners are not inherent characteristics of people: they must be learned. Introduce the concept of patience in very small doses (like literally one second to begin with), then slowly increase the amount of time they wait as they grow. For the first little while, you will have to allow yourself to be interrupted immediately so that your child has a positive experience, but trust that it will all be working towards the goal you desire.