Saha, Pipas2015-09-162023-10-192015-09-162023-10-192012ROLL NO.08612204https://gyan.iitg.ac.in/handle/123456789/320Supervisor: Ail Kumar SaikiaThe thesis contains six chapters. The first chapter provides a brief introduction about monoand bicyclic oxygen heterocycles and oxonium-ene cyclization reactions. Special emphasis has been given to six membered oxygen heterocycles and oxabicyclic compounds. The second chapter gives a description about the novel synthesis of oxabicyclo[3.3.1]nonanone via (3,5)-oxonium-ene reaction. The third chapter describes about the synthesis of oxabicyclo[3.3.1]nonenes and substituted tetrahydropyrans via (3,5)-oxonium-ene reaction. In the fourth chapter there is a description about the stereoselective synthesis of 6- oxabicyclo[3.2.1]octene via (3,5)-oxonium-ene reaction. The fifth chapter presents the synthesis of 2,3,5,6-tetrasubstituted tetrahydropyrans via (3,5)-oxonium-ene reaction. The sixth chapter describes about the diastereoselective synthesis of substituted dihydropyrans via oxonium-ene cyclization reaction..enCHEMISTRYThesis