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Part-IIAim of the Present Work3. Aim of the Present Work3.1 IntroductionPyrimidines and condensed pyrimidines have a long and distinguished history of theirimmense biological and medicinal significance. 1 The synthesis and biological evaluationof condensed pyrimidines, appropriately functionalized, especially at 2- & 4- positionshas attracted considerable attention of medicinal chemists worldwide, as they arepotentially bioactive molecules. 23.2 Biological and Pharmacological Significance of ThienopyrimidinesCondensed pyrimidines and quinazolines have shown a wide spectrum of biologicalactivities and have been exhaustively reviewed. 1 Thieno[2,3-d]pyrimidines are consideredto be bioisosteres of quinazolines. The concept of bioisosterism 3 has been exploited bymedicinal chemists as an approach to the drug design. This has lead to the synthesis ofvarious types of condensed pyrimidines, which show a wide range of biological activities.4-Amino and 4-oxo-5,6,7,8-tetrahydro-7-benzylpyrido[4’.3’:4,5]thieno[2,3-d]pyrimidines1 and 2 4,5 , some derivatives of thieno[2,3-d]pyrimidin-4-(3H)-ones 3 6 , 3,4-dihydro-4-oxothieno[2,3-d]pyrimidine carboxylates 4 7 and 5 8 and thieno[2,3-d]pyrimidin-4-(3H)-ones 6 9 have exhibited potent anti-allergic activity.H 2 NONNHR 1NNSR= alkyl, Ar-CH - 2 , alkylthio, pyridyl1OR 3NRNNSR= alkyl, Ar-CH - 2 , alkylthio, pyridylO2NHRR 2NSR 1 , R 2 = -(CH 2 )n-; n=4, 6;R 3 = H, alkyl;R 4 = COOH, CH 2 OH.3R 4S4NCOOC 2 H 5310