| Summary: | 博士 === 國立中興大學 === 化學系所 === 102 === Herein we utilized, for the first time, sodium 2-iodoxybenzoate as a highly specific oxidant for PhthNH2 to create a highly chemoselective aziridination reagent. This method efficiently effects aziridination of electron-rich, electron-deficient, allylic alcohol and alkenyl bromide C=C bonds in good to excellent yields. Inter and intra molecular chemoselectivity was demonstrated between electron-rich and electron-deficient alkenes by using this efficient and metal free protocol.
The Sc(OTf)3 catalyzed imination of sulfoxides with N-aminophthalimide in the presence of 2-iodoxybenzoic acid has been investigated. A variety of sulfoxides were efficiently iminated with N-aminophthalimide to afford the corresponding sulfoximines with excellent yields. The challenging imination of sterically demanding alkyl, benzyl and cyclic sulfoxides have been studied and the present protocol were found to be the best choice.
In aiming oseltamivir we sought to establish the functional groups with exact stereogenic centers in a purely reagent controlled fashion granting for maximum feasibility and flexibility. We, instead of doing cleavage over six-membered ring, decided to manipulate the functional groups for instance the 3-pentyl ether group and ethyl ester group through the reaction of 3-pentyl trichloroacetimidate and Heck carbonylation, respectively. We anticipated that the fragment 13e could be achieved through enantioselective formation of aziridine and diastereoselective ring opening of the same. The choice of (S)- cyclohex-2-ene-1-ol as the starting material in this process seemed to be an obvious one due to the fact that the carbocyclic system is already present.
Via combining a novel acid-promoted rearrangement of acetal functionality with the controlled installation of the epoxide unit to create the pivotal epoxide intermediates in enantiomerically pure form, a concise synthesis of (+)- and (–)-shikimic acids and (+)- and (–)-Phenylthioconduritol F has emerged. This simple strategy not only provides an efficient approach to Shikimic acids but it also can readily be adopted for the synthesis of (+)- and (–)-quinic acids. These concise total syntheses exemplify the use of pivotal allylic epoxide 3 and its enantiomer ent-3. A readily available inexpensive C2-symmetric L-tartaric acid (1) served as key precursor. In general, the strategy here provides a neat example of the use of a four carbon-chiron and offers a good account of synthesis of functionalized cyclohexane targets.
Herein we devised an enantiodivergent synthetic strategy called a “common chiral pool strategy” in the hope that it could be amenable to the construction of either a (+)-enantiomer or (–)-enantiomer as required from the same chiral compound. In the light of our common chiral pool strategy, we developed an efficient approach to generate both (+)-enantiomer and (–)- enantiomer of MK-7607, 4-epi-shikimic acid and shikimic acid. In general, less abundant and unnatural shikimic acid and their analogues were synthesized from highly abundant and inexpensive L-tartaric acid. Presented routes featured with a) enantiospecific and regiospecific formation and ring opening of oxirane b) generation of molecular asymmetry using Lewis acid. The strategies described here take place through concise and high-yield reaction sequences.
Total synthesis of synthetically challenging and biologically promising constituents of Amarylidaceae alkaloids namely trans-Dihydronarciclasine and Pancratistatin have been investigated. The oxygenated C-ring was constructed, in the light of our common chiral pool strategy, by tandem ring closing metathesis and organocatalyzed acetal rearrangement of tartaric acid derived allylic hydroxyls. The major difficulty in the synthesis of fully oxygenated Amaryllidaceae is in the control of stereochemistry at phenanthiridone ring and in introducing or maintaining the oxygen functional group in C-ring. To overcome the former issue, we envisioned to construct phenanthiridone B-ring through intramolecular ring opening of epoxide with aryl nucleophile. Further work is currently ongoing to achieve an efficient total synthesis of aforementioned potent anticancer molecules.
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