Ti?Oi-Pr?₄-Promoted PEDA Reaction And Its Application In The Synthesis Of Natural Products

This thesis focuses on the development of Ti?Oi-Pr?₄-promoted photoenolization Diels-Alder?PEDA?reaction and its application in the synthesis of natural products.Part 1:Anthracenols containing all-carbon quaternary centers are widely existed in natural products.Therefore,it is of great significance to develop efficient strategies for their synthesis.In view of this,we have developed a Ti?Oi-Pr?₄-promoted PEDA reaction to efficiently construct hydroanthracenol and related polycyclic compounds with multiple contiguous stereocenters,including one all-carbon quaternary center and even vicinal all-carbon quaternary stereocenters.The advantages of this developed PEDA reaction rely on good functional group compatibility,broad reaction scope and the high stereoselectivity.The preliminary mechanism studies show that Ti?Oi-Pr?₄ plays a crucial role in the reaction,which not only activates the dienophile,but also stabilizes the short-lived yet active?-hydroxy-o-QDMs intermediate with the help of the ortho-methoxy group.In addition,studies have also been conducted on the Ti?Oi-Pr?₄-promoted PEDA reaction with sterically hindered diene to construct tricyclic framework containing gem-dimethyl.Part 2:The first total synthesis of oncocalyxone B was achieved from simple materials based on the newly developed Ti?Oi-Pr?₄-promoted PEDA reaction,which demonstrates its synthetic potential.In addition,we also constructed the core skeleton of exiguaquinol and pleurotin using this method as a key step.Two strategies were designed to construct the skeleton of exiguaquinol including PEDA reaction and Nazarov reaction.The results show that Ti?Oi-Pr?₄-promoted PEDA reaction facilitates the synthesis of tetracyclic basic skeleton?B-C-D-E?.Regarding to the synthesis of pleurotin,construction of the A-B-C-D tetracyclic skeleton using PEDA reaction as a key step could not deliver the desired trans-perhydroindan?C-D?,and only gave cis-perhydroindan using the photoreaction precursor generated from aldol condensation or hydrogenation strategy.Construction of A-B-C tricyclic skeleton has been efficiently achieved,and subsequent five steps provided the precursor to introduce D ring in total 50%yield.