- Synthetic studies on callipeltin A: Stereoselective synthesis of (2 R,3 R,4 S)-3-hydroxy-2,4,6-trimethylheptanoic acid
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Asymmetric synthesis of (2R,3R,4S)-3-hydroxy-2,4,6-trimethylheptanoic acid, the -hydroxy acid unit that acylates the N-terminus of cyclic depsipeptide callipeltin A, has been devised. The approach involves the desymmetrization of a bicyclic precursor, which generates the three chiral centers
- Sabitha, Gowravaram,Yadagiri,Chandrashekhar,Yadav
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Read Online
- Directed hydrogenations and an Ireland-Claisen rearrangement linked to Evans-Tishchenko chemistry: The highly efficient total synthesis of the marine cyclodepsipeptide doliculide
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Two new convergent total syntheses have been developed for the cytotoxic, actin microfilament-stabilizing marine cyclodepsipeptide doliculide (1). A key strategic element of both routes is the establishment of the central stereogenic center of the characteristic polydeoxypropionate stereotriad by means of a hydroxyl-directed catalytic hydrogenation of a trisubstituted double bond. The requisite olefin substrates were obtained through a modified Suzuki-Miyaura coupling or through Ireland-Claisen rearrangement of a propionate ester, respectively; the latter was the direct result of a highly selective Evans-Tishchenko reduction of a hydroxy ketone that had been obtained in a stereoselective Paterson aldol reaction. Doliculide (1) was finally obtained in a total number of 17 or 15 (14) linear steps, respectively, which represents a substantial improvement over previous syntheses of this highly bioactive natural product.
- Chen, Tao,Altmann, Karl-Heinz
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supporting information
p. 8403 - 8407
(2015/06/02)
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- Stereospecific Pd-catalyzed cross-coupling reactions of secondary alkylboron nucleophiles and aryl chlorides
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We report the development of a Pd-catalyzed process for the stereospecific cross-coupling of unactivated secondary alkylboron nucleophiles and aryl chlorides. This process tolerates the use of secondary alkylboronic acids and secondary alkyltrifluoroborates and occurs without significant isomerization of the alkyl nucelophile. Optically active secondary alkyltrifluoroborate reagents undergo cross-coupling reactions with stereospecific inversion of configuration using this method.
- Li, Ling,Zhao, Shibin,Joshi-Pangu, Amruta,Diane, Mohamed,Biscoe, Mark R.
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supporting information
p. 14027 - 14030
(2015/01/08)
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- BORENIUM FRUSTRATED LEWIS PAIR CATALYSTS
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A process for the catalytic hydrogenation of a variety of organic substrates using frustrated Lewis pair catalysts comprising a borenium complex is described. The frustrated Lewis pair catalysts described can also be used in a variety of chemical transformations of organic molecules.
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Paragraph 0135
(2014/01/07)
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- Formal synthesis of leustroducsin B via Reformatsky/Claisen condensation of silyl glyoxylates
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A formal synthesis of leustroducsin B has been completed. The synthesis relies upon a recently developed Reformatsky/Claisen condensation of silyl glyoxylates and enantioenriched β-lactones that establishes two of the molecule's three core stereocenters and permits further elaboration to an intermediate in Imanishi's synthesis via reliable chemistry (Prasad reduction, asymmetric pentenylation, Mitsunobu inversion).
- Greszler, Stephen N.,Malinowski, Justin T.,Johnson, Jeffrey S.
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supporting information; experimental part
p. 3206 - 3209
(2011/08/07)
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- Nickel-catalyzed coupling producing (2Z)-2,4-alkadien-1-ols, conversion to (E)-3-alkene-1,2,5-triol derivatives, and synthesis of decarestrictine D
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The 3-alkene-1,2,5-triol structure is not only a major framework of biologically important molecules but also a new functional-group-rich unit for synthesis of polyols and sugars. A method furnishing such triol derivatives 8 was developed and successfully applied to synthesis of decarestrictine D (18). First, coupling reaction of the unprotected alcohols 2 with borates 4 was investigated to produce the dienyl alcohols 6 with NiCl2(dppf) in Et2O/THF (5:1) at room temperature. The hydroxyl-group-directed epoxidation of 6 followed by palladium-catalyzed reaction with AcOH (Scheme 1) furnished 3-alkene-1,2,5-triol derivatives 8. Since each step proceeded with high stereo- and regioselectivities, the stereochemistry of 8 has been correlated with the olefin geometry of 6. With the above transformation in mind, synthesis of the full carbon skeleton of decarestrictine D (18) could be designed easily and was completed successfully. Furthermore, a new seco acid 19b with the MOM protective group for the three hydroxyl groups was found to afford macrolide 48 in a yield higher than those reported previously.
- Kobayashi, Yuichi,Yoshida, Shinya,Asano, Moriteru,Takeuchi, Akira,Acharya, Hukura P.
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p. 1707 - 1716
(2008/02/01)
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- Synthesis of the C29-C37 bicyclic ether core of (+)-sorangicin A
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(Chemical Equation Presented) Construction of the unique bicyclic bis-ether core of the macrolide (+)-sorangicin A has been achieved. This fragment was prepared by utilizing a one-pot cascade of three bond forming events. An epoxide opening of the epoxy tosylate 2 led to the formation of the tetrahydropyran and subsequently to a second epoxide. Finally, a second epoxide opening closed the tetrahydrofuran ring. The bicyclic fragment was synthesized in just nine steps from (E)-cinnamaldehyde.
- Crimmins, Michael T.,Haley, Matthew W.
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p. 4223 - 4225
(2007/10/03)
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- Molecular addition compounds. 14. Convenient preparations of representative dialkylborane reagents using the new, highly reactive N- ethyl-N-isopropylaniline-borane reagent (BACH-EI(TM))
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Convenient procedures for the preparation of representative dialkylborane reagents, diisopinocampheylborane, [1S]-2-diisocaranylborane, 9-borabicyclo[3,3,1]nonane, dicyclohexylborane and disiamylborane, using the new, highly reactive N-ethyl-N-isopropylaniline-borane reagent (BACH-EI(TM)) in dioxane and tetrahydrofuran are described.
- Brown, Herbert C.,Kanth, Josyula V. B.,Zaidlewicz, Marek
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p. 5991 - 6000
(2007/10/03)
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