- Chemo-, regio-, and stereoselective silver-catalyzed aziridination of dienes: Scope, mechanistic studies, and ring-opening reactions
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Silver complexes bearing trispyrazolylborate ligands (Tpx) catalyze the aziridination of 2,4-diene-1-ols in a chemo-, regio-, and stereoselective manner to give vinylaziridines in high yields by means of the metal-mediated transfer of NTs (Ts = p-toluensulfonyl) units from PhI=NTs. The preferential aziridination occurs at the double bond neighboring to the hydroxyl end in ca. 9:1 ratios that assessed a very high degree of regioselectivity. The reaction with the silver-based catalysts proceeds in a stereospecific manner, i.e., the initial configuration of the C=C bond is maintained in the aziridine product (cis or trans). The degree of regioselectivity was explained with the aid of DFT studies, where the directing effect of the OH group of 2,4-diene-1-ols plays a key role. Effective strategies for ring-opening of the new aziridines, deprotection of the Ts group, and subsequent formation of β-amino alcohols have also been developed.
- Llaveria, Josep,Beltrán, álvaro,Sameera,Locati, Abel,Díaz-Requejo, M. Mar,Matheu, M. Isabel,Castillón, Sergio,Maseras, Feliu,Pérez, Pedro J.
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supporting information
p. 5342 - 5350
(2014/05/06)
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- Rhodium-catalyzed regio- and stereoselective oxyamination of dienes via tandem aziridination/ring-opening of dienyl carbamates
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The reaction of dienyl carbamates with PhI(OR)2 in the presence of rhodium catalysts affords vinyl aziridines which are in situ regio- and stereoselectively opened to afford oxyamination products resulting from a selective SN2 (Rh2(OAc)4/PhI(OPiv)2) or SN2′ (Rh2(OPiv)4/PhI(OAc) 2) opening. The scope and limitations of this tandem process are described.
- Guasch, Joan,Díaz, Yolanda,Matheu, M. Isabel,Castillón, Sergio
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supporting information
p. 7344 - 7347
(2014/07/07)
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- Efficient silver-catalyzed regio- and stereospecific aziridination of dienes
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Nitrene transfer: Unsymmetric dienes bearing a terminal hydroxy group can be regio- and stereospecifically converted into vinylaziridines upon nitrene transfer from PhINTs using a silver-based catalyst. Stoichiometric mixtures of dienes and PhINTs were employed at low catalyst loadings (0.5□%; see scheme). The method has been applied to the synthesis of (±)-sphingosine and gave good yields in a three-step procedure. Ts=4-toluenesulfonyl.
- Llaveria, Josep,Beltran, Alvaro,Diaz-Requejo, M. Mar,Perez, Pedro J.,Matheu, M. Isabel,Castillon, Sergio
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supporting information; experimental part
p. 7092 - 7095
(2010/11/05)
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- Synthesis of D/L-erythro-Sphingosine Using a Tethered Aminohydroxylation Reaction as the Key Step
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A diastereoselective synthesis of racemic D/L-erythro- sphingosine is described. The approach involves employing tethered aminohydroxylation (TA) to introduce the 2-amino and 3- hydroxy functions with required stereochemistry. Georg Thieme Verlag Stuttgart.
- Morales-Serna, Jose Antonio,Isabel Matheu, Yolanda Diaz M.,Castillon, Sergio
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experimental part
p. 710 - 712
(2009/09/06)
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- Lipase-catalyzed enantiomeric resolution of ceramides 1
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Lipase-catalyzed enantiomeric kinetic resolution of ceramides related to C16-sphinganine and C18-sphingenine is described. Two hydroxy groups in readily available racemic N-stearoyl-erythroC16-sphinganine were acetylated, and several kinds of lipases were screened for the hydrolysis of this substrate. Among them, a Burkholderia cepacia lipase (SC lipase A, Sumitomo Chemical Co., Ltd.) showed the highest reactivity and enantioselectivity. The rate of hydrolysis and selectivity were greatly affected by some additives. Especially, the combined use of a detergent, Triton X-100, and the solid support, Florisil, for immobilization showed the highest enantioselectivity (E = ca. 170), although the reaction rate turned low. Introduction of a double bond into the substrate (N-stearoyl-erythro-Cis-sphingenine) also retarded the hydrolysis. By utilizing the preferential hydrolysis of the acetate on the primary hydroxy group, another advantageous feature of this enzyme-catalyzed reaction, the resulting product could directly be used as the glycosyl acceptor for cerebroside synthesis.
- Bakke, Mikio,Takizawa, Masahiro,Sugai, Takeshi,Ohta, Hiromichi,Herold
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p. 6929 - 6938
(2007/10/03)
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- A New Route to Racemic erythro-Sphingosine and Ceramides. The 1,2-versus 1,4-Addition Reaction of Hexadec-2-enal with 2-Nitroethanol
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The reaction of hexadec-2-enal (5) with 2-nitroethanol (3) in triethylamine gave the 1,2-adducts (8) and (9), while the reaction in methanol-potassium carbonate gave the Michael adducts (6) and (7).Epimerization of the threo-acetonide (10) smoothly gave the erythro-acetonide (11), which gave the amino acetonide (12) on reduction.Phthaloylation, deacetalization, and deprotection of compound (12) gave rac-erythro-sphingosine (1).On the other hand, acylation and deacetalization of compound (12) gave the ceramide (16).
- Hino, Tohru,Nakakyama, Kiyoshi,Taniguchi, Mikio,Nakagawa, Masako
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p. 1687 - 1690
(2007/10/02)
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