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
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
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DOI：
10.1021/ja993239s
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发表时间：
2000-02
影响因子：
15
通讯作者：
S. Shuto;I. Sugimoto;and Hiroshi Abe;A. Matsuda
中科院分区：
文献类型：
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作者：
S. Shuto;I. Sugimoto;and Hiroshi Abe;A. Matsuda
对一种新的自由基扩环反应进行了机理研究，该反应由3-氧杂-2-硅环戊基甲基自由基扩环生成4-氧杂-3-硅环己基自由基。可以假定两种途径，一种是通过五价硅桥连自由基过渡态（或中间体），另一种是通过β-消除得到开环的甲硅烷基自由基。1和2分别是（3-氧杂-2-硅环戊基）甲基自由基C'和4-氧杂-3-硅环己基自由基D'的前体，它们的自由基反应表明C'扩环重排为D'是不可逆的。在硅上具有不对称中心的8a和8b的自由基反应的1H NMR分析表明，在环扩大反应期间，硅原子上的构型通过五价硅桥连自由基过渡态（或中间体）保留。此外，对氘标记底物12 D的自由基扩环反应的检查表明，扩环反应不涉及..
A mechanistic study was performed on a novel radical ring-enlargement reaction of (3-oxa-2-silacyclopentyl)methyl radicals into 4-oxa-3-silacyclohexyl radicals. Two pathways, one via a pentavalent silicon-bridging radical transition state (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 C‘ and a 4-oxa-3-silacyclohexyl radical D‘, respectively, showed that the ring-enlargement rearrangement of C‘ into D‘ is irreversible. 1H NMR analysis of the radical reactions of 8a and 8b, which have an asymmetric center at silicon, indicated that the configuration at the silicon atom is retained via a pentavalent silicon-bridging radical transition state (or intermediate) during the ring-enlargement reaction. Furthermore, examination of the radical ring-enlargement reaction with a deuterium-labeled substrate 12D showed that the ring-enlargement reaction did not involv...