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SEQUENTIAL GENERATION OF CARBON RADICALS AND CARBANIONS : DYNAMIC STEREOCONTROL IN THE REACTION SEQUENCE

碳自由基和碳负离子的连续生成：反应序列中的动态立体控制

基本信息

批准号：
10208212
负责人：
TAKAI Kazuhiko
金额：
$ 13.89万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

We investigated on two themes using dynamic stereocontrol : (i) the utilization of chromium(II) as a reductant, and (ii) stereo-controlled synthesis of fluorinated amino acids, and found several new reactions as follows : (1) The mild reductant chromium(II) chloride can discriminate between alkyl iodides, alkyl radicals, and conjugated carbon radicals. In the presence of chromium(II) the alkyl radical is so long-lived that it can undergo intermolecular addition to radical acceptors such as 1,3-dienes and α,β-unsaturated esters. (2) In an aprotic solvent, dimethylformamide, a coupling reaction between an α,β-unsaturated ketone and an aldehyde is achieved with chromium(II) chloride. An intermolecular aldol reaction and intramolecular cyclization proceed sequentially to give cis-2-hydroxyalkyl-substituted cyclopropanol stereoselectively. (3) In the presence of Et_3SiCl, a chromium enolate is trapped smoothly to give a silyl enol ether. This trapping changes the course of the reaction betw … More een an α,β-unsaturated ketone and an aldehyde from a sequential aldol-cyclopropanol formation to a cross pinacol-type coupling reaction. When aliphatic α,β-unsaturated ketones are employed, the anti / syn ratios of the 1,2-diols depend on the reaction temperature. (4) Stereo-controlled synthetic methods for fluorinated amino acids from cheap and easily available compounds. Under a hydrogen pressure, a catalytic amount of palladium(II) trifluoroacetate and BINAP promoted asymmetric hydrogenation of α-fluorinated iminoesters to afford the enantioenriched β-fluorinated α-amino esters. (5) Stereoselective syntheses of optically active trifluoro-norcoronamic acid and its diastereomer are studied. Stereospecific and diastereoselective cyclization of γ-cyanohydrins gave cyclopropyl nitriles. Further transformations of CN and Ar groups gave trifluoro-norcoronamic acid and trifluoro-allo-norcoronamic acid. (6) Chiral flurinated epoxide by chiral Shiff base of glycine nitrile gave both diastereomer of γ-hydroxynorvaline derivatives diastereoselectively depending on the base. This Shiff base is also applicable for preparation of optically pure bromodifluoroalanine derivative. Less

我们利用动态立体控制技术研究了两个主题：（i）铬（II）作为还原剂的利用，（ii）含氟氨基酸的立体控制合成，发现了如下几个新反应：（1）温和还原剂氯化铬（II）可以区分烷基碘、烷基自由基和共轭碳自由基。在铬（II）存在下，烷基自由基的寿命很长，以至于它可以与自由基受体如1，3-二烯和α，β-不饱和酯进行分子间加成。(2)在非质子溶剂二甲基甲酰胺中，α，β-不饱和酮和醛之间的偶联反应用氯化铬（II）实现。通过分子间羟醛缩合反应和分子内环化反应，立体选择性地合成了顺式-2-羟烷基取代的环丙醇。(3)在Et_3SiCl存在下，铬烯醇化物被顺利捕获，生成硅烯醇醚。这种捕获改变了反应的进程， ...更多信息从顺序的羟醛-环丙醇形成到交叉频哪醇型偶联反应得到α，β-不饱和酮和醛。当使用脂肪族α，β-不饱和酮时，1，2-二醇的反式/顺式比率取决于反应温度。(4)从廉价易得的化合物合成含氟氨基酸的立体控制方法。在氢气压力下，催化量的三氟乙酸钯（II）和BINAP促进α-氟代亚氨基酯的不对称氢化，得到对映体富集的β-氟代α-氨基酯。(5)研究了光学活性三氟去甲冠酰胺酸及其非对映体的立体选择性合成。γ-氰醇的立体选择性和非对映选择性环化反应生成环丙基腈。CN和Ar基团进一步转化得到三氟-去甲冠酰胺酸和三氟-别-去甲冠酰胺酸。(6)手性氟代环氧化物与甘氨酸腈的手性Shiff碱反应，根据碱的不同，可非对映选择性地生成两种γ-羟基正缬氨酸衍生物。该希夫碱也可用于制备光学纯的溴二氟丙氨酸衍生物。少