The present work entails the synthesis of different cross-conjugated (CC) heterodiene systems, and their transformations in various heterocyclic compounds using the hetero Diels-Alder (HDA) methodology. One of the main highlights of present work includes the development of simple and convenient procedure for the synthesis of stable CC azatrienes, and their tandem [2+2] cycloadditions and highly facile [3,3] sigmatropic Cope rearrangements with conjugated ketenes, leading to facile synthesis of various functionalized azocinone derivatives. A generalized and relevant study regarding the reactivity of thiazolic diazadienes with different ketenes was also conducted, and a remarkable increase in reactivity was observed with the introduction of electron donating group across the carbonyl group. Considering the biological and medicinal importance of C-5 or C-6 substituted pyrimidinones, the dienyl moiety of thiazolopyrimidinones was utilized further in Diels-Alder cycloadditions with both symmetrical and unsymmetrical dienophiles. Additionally, the synthesis of various pyrans, thiopyrans, thiophenes, thiazoles, 1,3-thiazines etc. is also described.