Convergent Domino Knoevenagel Hetero‐Diels—Alder and Domino Oxidation Hetero‐Diels—Alder Reactions Encountered in an Unexpected Formation of Novel 5‐Aryl‐1H‐pyrano[2,3‐d]pyrimidine‐2,4(3H,5H)‐diones and 5‐Aryl‐2,3‐dihydro‐2‐thioxo‐1H‐pyrano[2,3‐d]pyrimidin‐4(5H)‐ones.