SYNTHESIS AND REACTIONS OF SOME HETEROCYCLIC COMPOUNDS AND STUDYING SOME OF ITS APPLICATIONS

Abstract

The chemistry of the derivatives of 2 has been extensively reported m the literature 12 and also that of the isomeric thieno[2,3-d]pyrimidine

(1) has received considerable attention 2

The parent isomers 1 and 2

have been synthesized by more than one procedure. However, attempts to prepare the parent isomer 3 were unsuccessful owing to its instability since it has only one nonionic mesomeric fo m. On the other hand, / compounds 1 and' 2 have two mesomeric forms and are therefore

stabilized by resonance energy.

Topological resonance energies of isomeric thienopyrimidines were reported 3 and revealed that all thienopyrimidines to be aromatic compounds, but thieno[3,4-d]pyrimidine is 20% less aromatic than thieno[2,3-d]pyrimidine and thieno[3,2-cnpyrimidine. This result is also in agreement with a simple resonance-theoretical arg;Jn1ent according to which thieno[2,3-d]- and thieno[3,2-d]pyrimidines should be more aromatic because they possess two resonance structures while thieno[3,4- d]pyrimidine possess only one as indicated above. The HOMO-LUMO energy separation indicates that thienof3A-d]pyrimidine should be more reactive than either of the two isomeric compounds . It is conjuctured that, despite it has an aromatic character, thieno[3,4-d;,;Jyrimidine was never isolated because it is a rather reactive compound.