Reaction of 2‐dimethylaminomethylene‐1,3‐diones with Dinucleophiles. IV. Synthesis of 5,7‐dihydrothiopyrano[3,4‐c]pyrazol‐4(1H)‐ones, 5H‐Thiopyrano[4,3‐d]isoxazol‐4(7H)‐one and 6H‐Thiopyrano[3,4‐d]pyrimidin‐5(8H)‐ones