Boateng confirmed he called United manager Jose Mourinho in the final days of the Premier League transfer window to decline his offer.
He told BILD: "I had requests from Paris Saint-Germain and Manchester United - and I spoke with them. Not because I really wanted to leave Bayern.
"Therefore, it was not an attempt to escape, but the charm of a new challenge. I feel at home with FC Bayern, it's one of the biggest clubs in the world.
"I called José Mourinho and told him that his interest was an honour for me and he thanked me.
"It was a good conversation in which I explained the reasons why I would not come. It is very difficult to leave FC Bayern. With a change everything has to fit to top this club."