Pulse the tomatoes with their juices in a food processor until finely chopped.

Heat olive oil in a large saucepan over moderately high heat.

Add basil leaves and cook until they begin to wilt, about 10 seconds.

Add crushed red pepper, salt, and pepper.

Add the tomatoes and bring to a boil.

Cook, stirring, until slightly thickened, about 6 minutes.

Remove from heat and stir in the unsalted butter.

Season the sauce with salt and pepper.

Toss with pasta and serve.