Abstract
Abstract This thesis, which is divided into two parts, aims on the studies of masked ortho-benzoquinones (MOBs) and their applications. The first part is concerned with the novel radical reactions of bicyclo[2.2.2]octenones 20 and 21 utilizing Raney-Nickel or Bu3SnH/AIBN as reducing agents. In the second part, the investigation towards the total synthesis of (±)-eudesmadieneolide (91) is described. PartⅠ: Diels-Alder reactions of masked o-benzoquinones (MOBs) 6 with phenyl vinyl sulfide and phenyl vinyl selenide furnished bicyclo[2.2.2]octenones 20 and 21 with exceptional regio- and stereoselectivity. Treatment of compounds 20 and 21 with Raney-Nickel or Bu3SnH/AIBN afforded the major product compound 61 and the minor ODPM-rearrangement product 65, respectively without the isolation of any DPM rearrangement product. This phenomenon is different from literature reports. We believe that the substituents with various electronic properties present on MOBs 6 have a strong effect on these reactions. Furthermore, the functionalities, namely sulfur and selenide, which were introduced from the dienophiles used in the Diels-Alder reactions of MOBs and phenyl vinyl sulfide and phenyl vinyl selenide, also played an important role to direct the reaction pathway. Furthermore, we also found the desulfurization of compound 20a and 20c with Bu3Sn H/AIBN could provide novel compounds 74a and 74c, respectively. Surprisingly, formation of these two products is independent on the reaction pathway of DPM and ODPM rearrangement. However, a mechanism is proposed by us where tri-n-butyltin radical is presumably first added to the oxygen of carbonyl group followed by undergoing rearrangement to furnish 74a and 74c. PartⅡ: The tricyclic compound 108f was obtained via intramolecular Diels-Alder reaction of MOB 6f with furan 107. Protection of compound 108f followed by 1,2-addition and anionic oxy-Cope rearrangement successfully afforded cis-decalin 1117. Transformation of compound 117 into compound 120 was carried out in consecutive steps, including hydrogenation, hydrolysis and oxidative cleavage. Thus the core structure of natural product (±)-eudesmadieneolide (91) was obtained which can be easily converted to 91 upon few functional group transformation.