Poly(N‐bromo‐N‐ethyl‐benzene‐1,3‐disulfonamide) [PBBS] and N,N,N′,N′‐Tetrabromobenzene‐1,3‐disulfonamide [TBBDA] as New Efficient Reagents for One‐Pot Synthesis of Furano and Pyrano Pyrimidinones (Thiones).