Ueda Masafumi, Miyabe Hideto, Teramachi Masako, Miyata Okiko, Naito Takeaki
Kobe Pharmaceutical University, Motoyamakita, Higashinada, Kobe 658-8558, Japan.
J Org Chem. 2005 Aug 19;70(17):6653-60. doi: 10.1021/jo050603z.
The intermolecular radical addition to chiral nitrones 2, 4, 5, and 16 was studied. The isopropyl radical addition to Oppolzer's camphorsultam derivative 2 of glyoxylic nitrone proceeded with excellent diastereoselectivity to give the desired isopropylated product 3a accompanied by the diisopropylated product 3b. A high degree of stereocontrol in the reaction of cyclic nitrone 4 was achieved. The ethyl radical addition to nitrone 4 with triethylborane afforded the desired ethylated product 9a accompanied by the diethylated product 10a and the ethylated nitrone 11a. To evaluate the utility of cyclic nitrone 4, several alkyl radicals were employed in the addition reaction, which afforded the alkylated products 9b-d with excellent diastereoselectivities. In the presence of Mg(ClO(4))(2), the ethyl radical addition to BIGN 16 afforded selectively syn isomers. In contrast, the alkyl radical addition to 16 took place even in the absence of Lewis acid to give anti isomers.
研究了分子间自由基对手性硝酮2、4、5和16的加成反应。异丙基自由基对乙醛酸硝酮的Oppolzer樟脑磺内酰胺衍生物2的加成反应具有优异的非对映选择性，得到所需的异丙基化产物3a以及二异丙基化产物3b。在环状硝酮4的反应中实现了高度的立体控制。用三乙基硼烷将乙基自由基加成到硝酮4上，得到所需的乙基化产物9a以及二乙基化产物10a和乙基化硝酮11a。为了评估环状硝酮4的实用性，在加成反应中使用了几种烷基自由基，得到了具有优异非对映选择性的烷基化产物9b - d。在Mg(ClO₄)₂存在下，乙基自由基对BIGN 16的加成选择性地得到顺式异构体。相反，即使在没有路易斯酸的情况下，烷基自由基对16的加成也会发生，得到反式异构体。
