Hi, Leonor! I would like to suggest an approach from Waldorf education: children play better when you are doing your work. However, it must be in their presence and be something involving the body or hands, not just pushing a button. For example, instead of putting the dishes in the dishwasher (well, actually, I guess that part IS using hands and body) and pushing the button, try to make a habit of washing by hand. It's hard at first for children who have been played with a lot. Now, don't get me wrong, it IS important to play with your child!!! Just not all the time. Your son needs something/someone to imitate. That's what children at this age do and it's how they learn!
Another suggestion is to keep a nice rhythm going to your day. This does not mean a strict schedule, time-wise, but rather that you follow the same routine each day. This really brings a sense of power and predictability to a child and will help you, too. This way, you can work in the times during the day that are reserved for you and your son to play together, uninterrupted. I agree that he should have plenty of time with others during the week, if you can arrange it. In our house, that time is usually in the morning, about three days, sometimes four, each week.
For more info on this subject, I highly recommend two books:
"You Are Your Child's First Teacher" by Rahima Baldwin-Dancy and
"Beyond The Rainbow Bridge" by Barbara Patterson. The first book can be found at Barnes and Noble or ordered online (just do a search). The second is usually only found online or maybe order it at the bookstore.
My only other suggestion (sorry, I CAN get on my soapbox!) is to reduce or eliminate the number of battery-powered toys he has. These really take away a lot of imagination and do the work for the child. He will really "get into" his work (play) much more deeply if HE has to create the sounds, the movement, the voices, etc.. And that will help both him and you! (I know when we "Waldorf-ized" our home-- simple, wooden toys with no batteries, playcloths, etc.-- I saw a tremendous difference over time in my girls! People comment on how well my children play on their own and how involved they seem in their play.)
Hope this helps!

~Melissa