Lipase-catalyzed resolution of β-hydroxy selenides
摘要:
Eleven beta-hydroxy selenides were kinetically resolved using an immobilized lipase (Amano PS-C II) in toluene in the presence of vinyl acetate at 30 degrees C. This approach provided, in several cases, both enantiomers in high enantiomeric excess. The role of the size of substituents and the behaviour of cyclic beta-hydroxy selenides is also discussed. Enantiopure beta-hydroxy selenides are useful building blocks. As an application of this chemistry, enantiopure (1S,2R)-indene oxide was obtained in one step from the proper enantiopure beta-hydroxy selenide. (c) 2006 Published by Elsevier Ltd.
Mechanistic Study of the Ring-Enlargement Reaction of (3-Oxa-2-silacyclopentyl)methyl Radicals into 4-Oxa-3-silacyclohexyl Radicals. Evidence for a Pentavalent Silicon-Bridging Radical Transition State in 1,2-Rearrangement Reactions of β-Silyl Radicals
novel radical ring-enlargement reaction of (3-oxa-2-silacyclopentyl)methylradicals into 4-oxa-3-silacyclohexyl radicals. Two pathways, one via a pentavalent silicon-bridging radicaltransitionstate (or intermediate), the other via β-elimination to give a ring-opened silyl radical, can be postulated. The radical reactions of 1 and 2, which are precursors for a (3-oxa-2-silacyclopentyl)methyl radical
对 (3-oxa-2-silacyclopentyl) 甲基自由基向 4-oxa-3-silacyclohexyl 自由基的新型自由基扩环反应进行了机理研究。可以假设有两种途径,一种通过五价硅桥接自由基过渡态(或中间体),另一种通过β-消除产生开环甲硅烷基自由基。1 和 2 分别是(3-氧杂-2-硅杂环戊基)甲基自由基 C' 和 4-氧杂-3-硅杂环己基自由基 D' 的前体的自由基反应,表明 C 的扩环重排'变成D'是不可逆的。8a 和 8b 的自由基反应的 1H NMR 分析表明,在扩环反应期间,硅原子的构型通过五价硅桥基自由基过渡态(或中间体)保持不变。
Kinetics of a Novel 1,2-Rearrangement Reaction of β-Silyl Radicals. The Ring-expansion of (3-Oxa-2-silacyclopentyl)methyl Radical into 4-Oxa-3-silacyclohexyl Radical Is Irreversible
作者:Isamu Sugimoto、Satoshi Shuto、Akira Matsuda
DOI:10.1055/s-1999-2949
日期:1999.11
The kinetic study of the novel ring-expansion reaction of (3-oxa-2-silacyclopentyl)methyl radical into 4-oxa-3-silacyclohexyl radical with a precursor for 3-oxa-2-silacyclopentylmethyl radical 3 showed that the ring-expansion reaction is irreversible with a rate constant of 6.1×104 s-1 at 80 °C.
以 3-oxa-2-silacyclopentylmethyl radical 3 为前体,对 (3-oxa-2-silacyclopentyl)methyl radical into 4-oxa-3-silacyclohexyl radical 的新型环扩张反应进行的动力学研究表明,该环扩张反应是不可逆的,在 80 °C 时的速率常数为 6.1×104 s-1。
A One-Pot Method for the Stereoselective Introduction of a Vinyl Group via an Atom-Transfer Radical-Cyclization Reaction with a Diphenylvinylsilyl Group as a Temporary Connecting Tether. Synthesis of 4‘α-<i>C</i>-Vinylthymidine, a Potent Antiviral Nucleoside<sup>1</sup>
作者:Isamu Sugimoto、Satoshi Shuto、Akira Matsuda
DOI:10.1021/jo990787f
日期:1999.9.1
A one-pot method for the stereoselective introduction of a vinyl group at the beta-position of a hydroxyl group in halohydrins or alpha-phenylselenoalkanols via an atom-transfer radical-cyclization reaction was developed. When a solution of the diphenylvinylsilyl ether of (+/-)-trans-2-iodoindanol (2a) and (Bu3Sn)(2) in benzene was irradiated with a high-pressure mercury lamp, the corresponding atom transfer 5-exo-cyclization product was produced, which in turn was treated with tetrabutylammonium fluoride to give cis-2-vinylindanol (3) in 82% yield from 2a. Similar reactions with diphenylvinylsilyl ethers of (+/-)trans-1-phenylselenoindan-2-ol (4), trans-2-iodocyclopentanol (6), and trans-2-iodocyclohexanol (8) gave the corresponding vinyl derivatives. Furthermore, this reaction was successfully applied to the synthesis of 4'alpha-C-vinylthymidine, a potent antiviral nucleoside.
The First Radical Method for the Introduction of an Ethynyl Group Using a Silicon Tether and Its Application to the Synthesis of 2‘-Deoxy-2‘-<i>C</i>-ethynylnucleosides<sup>1</sup>
A novel radical method for the stereoselective introduction of an ethynyl group has been developed. When a solution of ethynyldimethylsilyl (EDMS) or [2-(trimethylsilyl)ethynyl]dimethylsilyl (TEDMS) ethers of trans-2-iodoindanol was treated with Et3B followed by tetrabutylammonium fluoride in toluene, atom transfer 5-exo-cyclization and subsequent elimination occurred to give cis-2-ethynylindanol in high yield. The method was shown to be useful in the introduction of an ethynyl group in various five- and six-membered-ring iodohydrins. Furthermore, 2'-deoxy-2'-C-ethynyl-uridine (6) and -cytidine (7), which were designed as novel antimetabolites, were readily synthesized by using this method as the key step. This would be the first example in which a radical reaction was used for introducing an ethynyl group.
Lipase-catalyzed resolution of β-hydroxy selenides
作者:Michelangelo Gruttadauria、Paolo Lo Meo、Serena Riela、Francesca D’Anna、Renato Noto
DOI:10.1016/j.tetasy.2006.10.010
日期:2006.10
Eleven beta-hydroxy selenides were kinetically resolved using an immobilized lipase (Amano PS-C II) in toluene in the presence of vinyl acetate at 30 degrees C. This approach provided, in several cases, both enantiomers in high enantiomeric excess. The role of the size of substituents and the behaviour of cyclic beta-hydroxy selenides is also discussed. Enantiopure beta-hydroxy selenides are useful building blocks. As an application of this chemistry, enantiopure (1S,2R)-indene oxide was obtained in one step from the proper enantiopure beta-hydroxy selenide. (c) 2006 Published by Elsevier Ltd.