Reactions of 6-Acetyl-4-Methyl-5-(1-Pyrrolyl)-2-Phenylthieno-[2,3-d]Pyrimidine in Heterocyclic Synthesis: Convenient Route to Some Schiff's Bases, Chalcones, Pyridines, Pyridin-2(1H)-Ones and 2H-Pyran-2-One Derivatives Incorporating a 5-(1-Pyrrolyl)-2-Phenylthieno[2,3-d]Pyrimidine Moiety