One-Pot Cascade Heterocyclization of γ- and β-Ketomalononitriles to 2,4-Dichloro-Substituted Pyrano[2,3-d]pyrimidines and Furo[2,3-d]pyrimidines Mediated by Triphosgene and Triphenylphosphine Oxide

A one-pot cascade heterocyclization strategy has been developed for the synthesis of 2,4-dichloro-substituted pyrano[2,3-d]pyrimidines and furo[2,3-d]pyrimidines from linear γ- and β-ketomalononitriles using triphosgene and triphenylphosphine oxide. The reaction afforded synthetic useful products with moderate to good yields, bypassing the conventional harsh conditions of chlorination. The mechanistic study revealed that the reaction proceeded with a non-isocyanate route, and the second step may conduct in a triphenylphosphine oxide-catalyzed manner.