A new and highly expedient synthesis of pyrido[2,3-d]pyrimidines

2,6-Diaminopyrimidin-4-one was reacted with a number of butynones in a range of different solvents at room temperature or 60°C. The Michael addition and subsequent cyclodehydration provided a new method for the synthesis of pyrido[2,3-d]pyrimidines in excellent yield without need for further purification. This new facile procedure lends itself well to combinatorial methods, providing the target heterocycle in one or two steps with total regiocontrol.