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Now showing items 1 - 16 of 5149

  • Total Syntheses of (+/-)-Rhodonoids A and B and C12-epi-Rhodonoid B

    Wu, Hao   Hsung, Richard P.   Tang, Yu  

    Total syntheses of (+/-)-rhodonoids A and B and C12-epi-rhodonoid B are described here. A unified strategy employed in these syntheses is an intramolecular oxa-[3 + 3] annulation for accessing the chromene unit. A Fe(OTf)(3)-promoted diastereoselective cationic [2 + 2] cycloaddition and a photochemical [2 + 2] cycloaddition were featured to construct the cyclobutane core of (+/-)-rhodonoids A and B and C12-epi-rhodonoid B, respectively. Fe(OTf)(3) also leads to an interesting bridged tetracycle, which was unambiguously confirmed by single crystal X-ray analysis.
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  • Total Syntheses of (+/-)-Rhodonoids C,D,E,F,and G and Ranhuadujuanine B

    Wu, Hao   Hsung, Richard P.   Tang, Yu  

    Here we describe the divergent, biosynthetically inspired syntheses of (+/-)-rhodonoids C-G and (+/-)-ranhuadujuanine B. The key steps of the Syntheses inelude the construction: of the chromene unit through a formal oxa-[3 + 3] annulation and a biomimetic acid-catalyzed ring Cyclization. Cationic [2 + 2]:cydoadclition is accomplished to form the cyclobutane core of (+/-)-rhcidonoids E and F.
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  • Total syntheses of proposed (+/-)-trichodermatides B and C

    Li, Qian   Xu, Yan-Shuang   Ellis, Gregory A.   Bugni, Timothy S.   Tang, Yu   Hsung, Richard P.  

    Total syntheses of putative (+/-)-trichodermatides B and C are described. These efficient syntheses feature the oxa-[3+3] annulation strategy, leading to B and C along with their respective C2-epimers. However, these synthetic samples are spectroscopically very different from the natural products. OFT calculations of C13 chemical shifts are conducted and the predicted values are in good agreement with those of synthetic samples, thereby questioning the accuracy of structural assignments of trichodermatides B and C. Published by Elsevier Ltd.
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    Feltenberger, John B.   Ko, Changhong   Deng, Jun   Ghosh, Sunil K.   Hsung, Richard P.  

    The development of an intramolecular variant of Gassman's cationic [2 + 2] cycloaddition is described herein. Mechanistic aspects of the stepwise nature of this cycloaddition process between vinyl acetals and unactivated olefins have been studied. We have also explored the scope of this reaction with regard to various oxygen-, nitrogen-, and carbon-tethered acetals to provide access to a diverse array of bicyclic scaffolds. Additionally, we have identified vinyl hemiaminals as having favorable reactivity for cationic [2 + 2] cycloaddition.
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  • (4+3) Cycloaddition Reactions of Nitrogen-Stabilized Oxyallyl Cations

    Lohse, Andrew G.   Hsung, Richard P.  

    The use of heteroatom-substituted oxyallyl cations in (4+3) cycloadditions has had a tremendous impact on the development of cycloaddition chemistry. Extensive efforts have been exerted toward investigating the effect of oxygen, sulfur, and halogen substituents on the reactivity of oxyallyl cations. Most recently, the use of nitrogen-stabilized oxyallyl cations has gained prominence in the area of (4+3) cycloadditions. The following article will provide an overview of this concept utilizing nitrogen-stabilized oxyallyl cations.
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  • Oppolzer-Type Intramolecular Die-Alder Cycloadditions via Isomerizations of Allenamides

    Feltenberger, John B.   Hsung, Richard P.  

    A new approach to Oppolzer's Intramolecular Dlels-Alder cycloaddition (IMDA) through gamma-isomerlzation of readily available N-tethered allenamides is described. These IMDA reactions are carried out in tandem with the allenamide isomerization or 1,3-H shift, leading to complex nitrogen heterocycles in a highly stereoselective manner.
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  • Synthesis of the C1-C16 fragment of spirastrellolide A

    Liu, Jia   Yang, Jin Haek   Ko, Changhong   Hsung, Richard P.  

    Synthesis of the Cl-C16 fragment of spirastrellolide A is described here featuring Sharpless asymmetric epoxidation, an acid promoted O-1,4-addition, and Mukaiyama 1,3-anti-aldol. (c) 2006 Elsevier Ltd. All rights reserved.
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  • Strategies and approaches for constructing 1-oxadecalins

    Tang, Yu   Oppenheimer, Jossian   Song, Zhenlei   You, Lingfeng   Zhang, Xuejun   Hsung, Richard P.  

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  • Copper salt-catalyzed azide-[3+2] cycloadditions of ynamides and bis-ynamides

    Zhang, Xuejun   Li, Hongyan   You, Lingfeng   Tang, Yu   Hsung, Richard P.  

    A one-pot synthesis of amide-substituted triazoles from alkyl bromides and ynamides is described here along with syntheses of novel bis-yn-amides and their applications in [3 + 2] cycloadditions with azides to construct unique bis-triazoles.
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  • Regioselectivities of (4+3) Cycloadditions between Furans and Oxazolidinone-Substituted Oxyallyls

    Lohse, Andrew G.   Krenske, Elizabeth H.   Antoline, Jennifer E.   Houk, K. N.   Hsung, Richard P.  

    The (4 + 3) cycloadditions of oxazolidinone-substituted oxyallyls and unsymmetrically substituted furans lead to syn regioselectivity when the furan has a 2-Me or 2-COOR substituent, while anti regioselectivity is obtained with a 3-Me or 3-COOR group. OFT calculations are performed to explain the selectivities. The reactivities and regioselectivities are consistent with the ambiphilic reactivity of amino-oxyallyls with furans.
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  • A ketal-tethered RCM strategy toward the synthesis of spiroketal related natural products

    Ghosh, Sunil K.   Ko, Changhong   Liu, Jia   Wang, Jiashi   Hsung, Richard P.  

    An unconventional approach to construct spiroketals and spiroaminals via ring-closing metathesis [RCM] of cyclic ketals and aminals, respectively, is described here. This method possesses a good generality with no loss of stereochemical integrity at the spirocenter under the standard RCM conditions. This approach has been applied to the synthesis of an insect pheromone to demonstrate its synthetic potential, and also to the synthesis of the C11-epi-C22-C23 fragment in spirastrellolide A. Both are proof-of-concept applications to feature a ketal-tethered RCM as an alternative strategy for construction of spiroketals. (c) 2006 Elsevier Ltd. All rights reserved.
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  • An Efficient Synthesis of de novo Imidates via Aza-Claisen Rearrangements of N-Allyl Ynamides

    DeKorver, Kyle A.   North, Troy D.   Hsung, Richard P.  

    A novel thermal 3-aza-Claisen rearrangement of N-allyl ynamides for the synthesis of a-allyl imidates is described. Also, a sequential aza-Claisen, palladium-catalyzed Overman rearrangement is described for the synthesis of azapin-2-ones.
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  • A mutually pi-facial selective cyclopropanation of chiral enamides using dirhodium(II) carbenoids

    Lu, Ting   Song, Zhenlei   Hsung, Richard P.  

    A mutually T-facial selective cyclopropanation of chiral enamides using dirhodium(II) carbenoids is described here. This work illustrates the influence of enamide substituents on stereoselectivity and reveals insights into this cyclopropanation.
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  • Total Synthesis of (+/-)-Phomactin A. Lessons Learned from Respecting a Challenging Structural Topology

    Buchanan, Grant S.   Cole, Kevin P.   Tang, Yu   Hsung, Richard P.  

    Our struggles and ultimate success in achieving a total synthesis of phomactin A are described. Our strategy features an intramolecular oxa-[3 + 3] annulation to construct its unique ABD-tricyclic manifold. Although the synthesis would constitute a distinctly new approach with the 12-membered D-ring of phomactin A being assembled simultaneously with the 1-oxadecalin at an early stage, the ABD-tricycle represents a unique structural topology that would pose a number of unprecedented challenges. One challenge concerned elaborating this tricycle to have oxygenation at the proper carbon atoms. To overcome this, we would utilize a Kornblum-DeLaMare ring-opening of a peroxide bridge as well as a challenging late-stage 1,3-allylic alcohol transposition. Further, the structural intricacies of the ABD-tricycle were uncovered by a conformational analysis that would be critical for the C5a-homologation.
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  • Encyclopedia of Reagents for Organic Synthesis || Diisopropylmagnesium

    Hsung, Richard P.  

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  • An intramolecular aza-[3+3] annulation approach to azaphenalene alkaloids. Total synthesis of myrrhine

    Gerasyuto, Aleksey I.   Hsung, Richard P.  

    A detailed account on the stereoselective total syntheses of azaphenalene alkaloids via an intramolecular aza-[3 + 3] annulation strategy is described here. All five members of the Coccinellidae family of defensive alkaloids were prepared from the same common intermediate, which was derived from a stereoselective aza-[3 + 3] annulation reaction.
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