Abstract
The studies on the Diels-Alder reactions of masked o-benzoquinones (MOBs) 50 with electron-rich dienophiles and synthetic applications of Diels-Alder cycloadducts 56a-e are described. This thesis deals with the Diels-Alder reactions of MOBs with electron-rich dienophiles and the synthesis of bicyclo[2.2.2]octadienone derivatives. Diels-Alder reactions of MOBs 50 with four electron-rich dieno- philes namely, benzyl vinyl ether, 2,3-dihydrofuran, 3,4-dihydropyran and phenyl vinyl sulfide and a conjugated dienophile styrene afforded highly functionalized bicyclo[2.2.2]octenones 51a-g, 54a-g, 55a, 56a-g and 57a-h in high regio- and stereoselectivities. Based on RHF/3-21G* calculations, it is suggested that LUMO of MOBs and HOMO of benzyl vinyl ether, 2,3-dihydrofuran and styrene are involved in the inverse electron-demand Diels-Alder reactions. We have carried out the oxidation of Diels-Alder cycloadducts 56a-e derived from MOBs and phenyl vinyl sulfide with m-CPBA at -78 ℃ to produce the corresponding sulfoxides 63a-e in high yields. The sulfo- xides 63a-e at reflux temperature in mesitylene furnished bicyclo[2.2.2]- octa-2,5-dien-1-ones 64a-e in very good yields. The compounds 64a-e are immediate precursors for heteroaromatic-fused barrelenes, which are very useful starting materials for the photochemical rearrangements.