首頁> 外文學位 >I. Studies on the organocatalytic formation of quaternary stereocenters. ii. Studies on the claisen rearrangement as a route to quaternary stereocenters. iii. Asymmetric synthesis of aldehydes bearing quaternary carbon centers via the decarboxylative asymmetric allylic alkylation.

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I. Studies on the organocatalytic formation of quaternary stereocenters. ii. Studies on the claisen rearrangement as a route to quaternary stereocenters. iii. Asymmetric synthesis of aldehydes bearing quaternary carbon centers via the decarboxylative asymmetric allylic alkylation.

機譯：I.季銨立體中心的有機催化形成研究。 ii。關于克萊森重排作為四元立體中心路徑的研究。 iii。通過脫羧不對稱烯丙基烷基化反應不對稱合成帶有季碳中心的醛。

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The asymmetric synthesis of all carbon quaternary stereocenters poses a particular challenge due to the steric congestion inherent in the formation of such centers and has been the object of intense research these last 20-30 years. However, the amount of literature for the synthesis of aldehydes bearing quaternary stereocenters via enolate type chemistry is much more limited due to problems associated with the alkylation of such substrates including such types as Cannizzaro and Tischenko related reactions or self aldol condensations. The formation of aldehydes with quaternary stereocenters via use of enolate equivalents such as the DAAA (decarboxylative asymmetric allylic alkylation) of ally enol carbonates has also not been fully explored. Herein, we describe the creation of all carbon stereocenters starting from 3-hydroxy aryl acrylates via several routes. The first method employs organocatalysts; reactions that have been investigated using this route are phase transfer catalyzed alkylations and organocatalytic Michael additions catalyzed by Cinchona alkaloid catalysts. The phase transfer catalyzed alkylation is less successful than the Michael addition due to competing C- vs. O-alkylation. The second method involves the well known Claisen rearrangement via the O-alkylation of 3-hydroxy aryl acrylates and the subsequent [3,3] sigmatropic rearrangement. The O-alkylated products are obtained in yields ranging from 65-84%, and the corresponding Claisen rearrangement products in yields ranging from 55-91%. Multiple attempts at achieving an asymmetric Claisen rearrangement employing Lewis acid metal catalysts failed either due to insufficient activation of the Claisen substrate or due to cleavage of the oxygen allyl bond. The last method involves the DAAA of allyl enol carbonates derived from 3-hydroxy aryl acrylates. A stereoselective synthesis of these carbonates was devised that can form the Z- or E- stereoisomer in very high Z/E ratios (50:1 and 1:99 respectively). The stereochemical outcome depends on the choice of base, addition of TMEDA and reaction temperature. The Z- and E- stereoisomers have different reactivities towards the DAAA reaction, with the E-stereoisomer displaying both greater reactivity and enantio-differentiation with chiral ligands. The DAAA of E- stereoisomer analogues takes place in excellent yields ranging from 96-99% and enatioselectivities ranging from 42-78% ee.

機譯：所有碳四元立體中心的不對稱合成由于其中心固有的空間擁塞而構(gòu)成了特殊的挑戰(zhàn)，并且在過去的20-30年中一直是研究的對象。然而，由于與這類底物的烷基化有關的問題，包括與Cannizzaro和Tischenko有關的反應或自醛醇縮合的這類底物的烷基化有關的問題，因此通過烯醇鹽型化學合成帶有四級立體中心的醛的文獻數(shù)量更為有限。還沒有充分探索通過使用烯醇式等效物如烯丙基碳酸酯的DAAA（脫羧不對稱烯丙基烷基化）形成具有季立體中心的醛。在這里，我們描述了通過幾種途徑從3-羥基芳基丙烯酸酯開始的所有碳立體中心的產(chǎn)生。第一種方法使用有機催化劑。使用該途徑研究的反應是金雞納生物堿催化劑催化的相轉(zhuǎn)移催化的烷基化反應和有機催化的邁克爾加成反應。由于C-對O-烷基的競爭，相轉(zhuǎn)移催化的烷基化不如Michael加成成功。第二種方法涉及通過3-羥基芳基丙烯酸酯的O-烷基化進行的眾所周知的克萊森重排以及隨后的[3,3]σ重排。獲得O-烷基化產(chǎn)物的產(chǎn)率為65-84％，并且相應的克萊森重排產(chǎn)物獲得的產(chǎn)率為55-91％。由于克萊森底物的活化不足或由于氧烯丙基鍵的斷裂，使用路易斯酸金屬催化劑實現(xiàn)不對稱克萊森重排的多次嘗試失敗。最后一種方法涉及衍生自丙烯酸3-羥基芳基酯的烯丙基碳酸酯的DAAA。設計了這些碳酸鹽的立體選擇性合成，其可以以非常高的Z / E比（分別為50：1和1:99）形成Z-或E-立體異構(gòu)體。立體化學結(jié)果取決于堿的選擇，TMEDA的添加和反應溫度。 Z-立體異構(gòu)體和E-立體異構(gòu)體對DAAA反應具有不同的反應性，其中E-立體異構(gòu)體顯示出更高的反應性和與手性配體的對映異構(gòu)。 E-立體異構(gòu)體類似物的DAAA以96-99％的優(yōu)異產(chǎn)率和42-78％ee的對映選擇性發(fā)生。

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作者
Alberch, Eduardo.;
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The University of Wisconsin - Milwaukee.;

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授予單位 The University of Wisconsin - Milwaukee.;
學科 Chemistry Organic.
學位 Ph.D.
年度 2013
頁碼 273 p.
總頁數(shù) 273
原文格式 PDF
正文語種 eng
中圖分類
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I. Studies on the organocatalytic formation of quaternary stereocenters. ii. Studies on the claisen rearrangement as a route to quaternary stereocenters. iii. Asymmetric synthesis of aldehydes bearing quaternary carbon centers via the decarboxylative asymmetric allylic alkylation.

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