Total Syntheses Of Steenkrotin B And Pepluanol A

The dissertation was focused on the studies of the total syntheses of steenkrotin B and pepluanol A which were belong to the terpenoids of Euphorbiaceae,the main contents include two chapters:Chapter 1:studies towards the total synthesis of steenkrotin B.Section 2,the route for the total synthesis of steenkrotin A was optimized based on the previous studies.Section 3,the[5,6,7]tricyclic skeleton was constructed via the intramolecular nitrile oxide-alkene cycloaddition reaction and the aldol reaction.Section 4,the Diels-Alder reaction and ketyl-olefin reaction as the key steps allowed access to the[5,6,7]tricyclic skeleton.Finally,the Mukaiyama hydration was employed to form the peroxy alcohol at C6.However,the NMR of the final structure wasn't matched with the NMR of steenkrotin B.Section 5,it was found that the endoperoxide bridge was located between C14 and C15 by the analysis of the 2D NMR.The endoperoxide hemiketal moiety was then installed by the Mukaiyama hydration based on the[5,6,7]tricyclic skeleton.The late-stage functionalizations provided the revised structure of steenkrotin B which was still not the same as the real one.Finally,we gave up looking for the real structure and constructed the 1.4-120 in 19 steps.Chapter 2:studies towards the total synthesis of pepluanol A.Section 2,the Diels-Alder allowed access to the[6,7]bicyclic skeleton.Selective dihydroxylation of alkenes followed by the oxidation of the vicinal diols made the precursor of cyclization.Ketyl-olefin reaction was employed to form the[5,6,7]tricyclic skeleton.The gem-dimethyl cyclopropane moiety was then installed by a two-step sequence involving dibromocarbene and dimethylation.Subsequent Saegusa oxidation and Dauben-Michno oxidation led to the formation of pepluanol A in 23 steps.Section 3,the second-generation synthesis of pepluanol A was accomplished.Selective epoxidation of alkenes followed by the oxidation of alkenes based on the[6,7]bicyclic structure afforded the precursor of cyclization.Construction and functionalization of the[5,6]bicyclic structure were then achieved by the titanium(?)-catalyzed reductive cyclization.The late-stage functionalizations were employed to finish the total synthesis of pepluanol A in 16 steps.