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烯丙基溴与金属钐在室温条件下、THF溶剂中反应生成中间体烯丙基溴化钐,烯丙基溴化钐再与α,β-不饱和醛、酮反应生成高烯丙基醇.烯丙基溴化钐与α,β-不饱和醛、酮发生1,2-加成反应,其与α,β-不饱和酮的反应几乎定量进行,表明该反应具有很好的区域选择性.产物的结构通过IR,1H NMR和MS光谱确证. 相似文献
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溴化(a-噻吩甲酰基)甲基三苯鉮1与3-取代苯甲叉基-2,4-戊二酮 2以碳酸钾为碱,在苯中55℃条件下反应,可以较好的收率、高立体选择性地生成反-2-(a-噻吩甲酰基)-3-取代苯基-4-乙氧羰基-5-甲基-2,3-二氢呋喃3。产物结构均经波谱予以确定。本文还提出了生成产物的可能机理。 相似文献
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作为一类重要的含氮杂环化合物, 3-氨基-2-二氢喹啉酮结构存在于一些药物和生物活性分子中.目前还没有手性催化的方法直接合成无保护基的此类结构.在过渡金属的催化作用下,乙烯基苯并噁嗪酮脱除一分子二氧化碳,生成的两性离子中间体可以参与多种反应合成含氮杂环化合物.我们设想乙烯基苯并噁嗪酮和2-氨基丙二酸酯直接发生不对称烯丙基化反应/去对称化反应,则可直接实现无保护基2-喹啉酮骨架环状氨基酸的手性合成.然而2-氨基丙二酸酯作为亲核试剂时,如何实现碳选择性进攻而不是固有的氮选择性进攻将成为此反应中一个重要挑战.本文通过钯催化的不对称烯丙基化/去对称化反应合成具有2-喹啉酮骨架的环状氨基酸.采用手性膦配体与钯作为催化剂,成功实现了乙烯基苯并噁嗪酮与2-氨基丙二酸酯的不对称α-烯丙基取代反应.随后无需提纯,烯丙基取代产物直接在三氟乙酸的作用下,发生分子内的去对称化内酰胺化反应,最终生成具有无保护基的2-喹啉酮骨架环状氨基酸产物.该催化方法反应条件温和,催化体系简单高效(钯催化剂负载量可降低至1 mol%,非对映选择性可高达15/1,对映选择性高达96%ee),并且具有良好的官能团兼容性.经盐酸处理... 相似文献
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羟基取代的黄烷酮与NO反应, 得到了羟基邻位或对位单硝基化产物. 随着反应时间的延长, 有羟基邻位和对位双硝基化以及羟基两个邻位双硝基化产物生成. 多羟基取代的黄烷酮可以生成多硝基化产物. 相似文献
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Samarium metal has been used for the reductive dimerization of aromatic ketones in the presence of additives; the most probable mechanism has been advanced to explain the diastereoselectivity of this dimerization reaction. 相似文献
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Samarium(II) diiodide has been employed to promote the intramolecular cyclization reactions of aldehydes or ketones onto α,β-unsaturated ketones. The cyclization reactions described herein provide a general approach to the syntheses of perhydronaphthalenones with a cis-relationship between the OH at C-5 and the proton or methyl group at C-4a with good diastereoselectivity under mild reaction conditions. 相似文献
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Samarium(II) iodide has been employed to promote vinylogous pinacol coupling reaction of aldehyde onto alpha,beta-unsaturated ketones. The diastereoselectivity of 6-endo products was changed by addition of a proton source and/or HMPA and by the reaction temperature. The cyclization reactions described herein provide a general approach to the syntheses of 3,3-dimethylhydrindanes with a cis-relationship between the OH at C-4 and the proton at C-3a with good diastereoselectivity and under mild reaction conditions. 相似文献
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Samarium (II) iodide has been successfully utilized as a strong one-electron transfer reducing agent for the cyclodimerization of α, β-unsaturated ketones. The absence of any alcohol as proton source is essential. The reaction is regioselective over the competitive carbon-carbon double bond reduction and stereocontrolled. The configuration of the cyclodimerization products, has been confirmed by X-ray analysis. 相似文献
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A novel reductive dimerization/oxidative dehydrogenation of aldimines mediated by lanthanoid metals.
A lanthanoid metal-mediated novel reductive dimerization/oxidative dehydrogenation of a variety of aldimines has been achieved. Aromatic aldimines (1) were dimerized in the presence of 0.5 mol of ytterbium metal (Yb) and 1-naphthaldehyde (1-NpCHO) to give the corresponding vicinal diimines (2) in good to high yields. Samarium metal (Sm) or samarium(II) diiodide (SmI2) gives unsatisfied yields under the same reaction conditions. As an oxidant, 1-NpCHO gives the best result. In addition, HMPA plays an important role as a cosolvent in this reaction. Reaction of various aldimines with Yb metal is discussed in detail. Moreover, it has been found that the electron-donating substitutents on the benzene ring promote the reaction and that the electron-withdrawing substitutents retard the reaction. The reaction of deuterated N-benzylideneaniline with Yb metal confirmed that transformation of the hydride occurred from aldimines to the oxidant aldehyde. The mechanism of the reaction was discussed. 相似文献
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Nada Jaber 《Tetrahedron》2004,60(13):3075-3083
Samarium diiodide, as well as lanthanide triiodides catalyze a one-pot procedure allowing to perform sequentially the Mukaiyama-Michael addition of a ketene silyl acetal on a cyclic α,β-unsaturated ketone, followed by the addition of a glyoxylic, aromatic or heteroaromatic imine. According to the nature of the silyl group the adducts resulting from this tandem process are isolated as ketones or as enoxysilanes. The presence of a coordinating group on the imine increases the rate of the reaction. 相似文献
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Samarium(II) iodide was used to access eight-, nine-, and ten-membered carbocycles via a domino reaction composed of a cyclization/fragmentation process. 2-(Iodoalkyl)-, 2-(iodomethyl)allyl-, and 2-(2-iodomethyl)benzyl-2-methyl-3-(methanesulfonyloxy)cycloalkanones were subjected to Barbier-type reductive coupling conditions. Intermediate cycloalkanedione derivatives were also treated under similar conditions, providing bicyclic hydroxy ketones with complete diastereoselectivity and high yields. This method represents a general and efficient approach to a variety of highly functionalized, stereodefined carbocycles. 相似文献
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[reaction: see text] Samarium diiodide promotes smooth reductive cyclizations of gamma-naphthyl-substituted ketones to afford tri- and tetracyclic compounds in high yields and with excellent stereoselectivities. Cyclic ketones furnish steroid-like compounds with "unnatural" cis/cis annulation of rings B/C/D. The remaining styrene-type double bond of ring B allows further stereoselective reactions. Cases with matched and mismatched relative configuration could be identified leading to dramatic differences in the ring closure ability. 相似文献
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Dysprosium metal promoted Barbier-type allylation of ketones and aldehydes has been investigated. It has been shown that dysprosium metal (activated by mercuric chloride) is effective in promoting the reaction of ketones with allyl iodide. The corresponding homoallylic alcohols are obtained in satisfactory yields. This reaction is regioselective and chemoselective. An α , β -unsaturated ketone affords a 1,2-addition product selectively. Reactive groups (such as Cl, Br, and methoxy) of aromatic ketones remain unchanged under the reaction conditions. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:475–478, 1998 相似文献
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Samarium(II)-induced coupling of acid chlorides with allylic halides gave diallylated tertiary alcohols. Monoallylated allylic ketones could not be obtained. 相似文献