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Gerhard Quinkert Nana Heim Jürgen Glenneberg Uwe Dller Mathias Eichhorn Uta-Maria Billhardt Christine Schwarz Gottfried Zimmermann Jan W. Bats Gerd Dürner 《Helvetica chimica acta》1988,71(7):1719-1794
Synthesis of the Lichen Macrolide (+)-Aspicilin Using Photolactonization as a Key Reaction (+)-Aspicilin, obtained from a lichen source of the Black Forest, has been proven to have the absolute configuration depicted by formula la . It is easily built up from phenol ( 14a ), 1,9-nonanediol ( 13a ), and (?)-(S-) methyloxiarane ( 6 ) (cf. Scheme 2). The latter building block provides the first stereogenic center C(17). The heterocycle is produced by photolactonization, fairly early during the course of the synthesis. The second stereogenic center is generated diastereoselectively at C(6) in compound 8 , conveniently available from photolactone 9a or 9b / 9c . Its absolute configuration depends on the kind of reducing agent and is controlled by long-range conformational transmission of chiral information. To explore the cause of stereoselection, 2D-NMR spectroscopy, X-ray structural analysis, and/or computer-aided conformational search followed by energy minimization have been used extensively, revealing the importance of the local conformation of the lactone moiety. Compound 8 , on treatment with Yamamoto's reagent, affords pre-target compound 7a almost exclusively. The latter compound, on pyridine-accelerated dihydroxylation with OsO4, gives preferentially (+)-Aspicilin. 相似文献
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Gerhard Quinkert Frank Küber Wolfgang Knauf Manfred Wacker Uwe Koch Heinrich Becker Hans Peter Nestler Gerd Dürner Gottfried Zimmermann Jan W. Bats Ernst Egert 《Helvetica chimica acta》1991,74(8):1853-1923
Synthesis of the Macrolide Antibiotic (?)-A2677IB Using Photolactonization as a Key Reaction and Computer Simulation as an Effective Aid in Optimization The title compound has been synthesized in a sequence of 21 steps starting from phenol. The cyclic skeleton has been built up in the earlier part of the synthesis by photolactonization. This reaction supplies C(6), with a functionality, not present in the target structure, but useful for oxygenation at C(4) and generation of the stereogenic center C(5). The Barton/McCombie reaction provides a product deoxygenated at C(6), but only after an adjacent oxirane ring has been opened at the cost of an increase in the number of overall steps. X-Ray structural information and computational modelling of appropriate molecules proved to be essential to selection of optimal conditions for various transformations. 相似文献
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Bis(trimethylsilyl)hypophosphite und Alkoxycarbonylphosphonous Acid Bis(trimethylsilyl) esters as Building Blocks in Organophosphorus Chemistry The oxidation of pure bis(trimethylsilyl)hypophosphite ( BTH ) with chalcogenides forming (Me3SiO)2P(X)H (X = O, S, Se, Te) is described as well as its reactions with alkylhalides RX (X = Cl, Br, I) and Cl? C(O)OR (R = Me, Et, Bzl). By reaction with oxygen, sulfur, and selenium the alkoxycarbonylphosphonous acid bis(trimethylsilyl)esters form RO? C(O)? P(X)(OSiMe3)2 (X = O, S, Se) whereas with Cl? C(O)OR the bis(alkoxycarbonyl)-phosphinic acid trimethylsilylesters are obtained. After partial hydrolysis the resulting instable RO? C(O)? P(O)H(OSiMe3) gives RO? C(O)? P(O)(OSiMe3)? CH2? NH? A? COOR′ (A = CH2, CH2CH2, CHCH3, CH2CH2SH, CHCH(CH3)2,…) when allowed to react with hexahydro-s-triazines of the aminoacid esters. Reactions of the alkoxycarbonyl-P-silylesters with NaOR or NaOH result in the corresponding mono-, di-, or trisodium salts. With mineral acids decarboxylation occurs, but H? P(O)(OH)? CH2? NH? A? COOH can be obtained, too. The structure of the compounds described are discussed by their n.m.r. data. 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2018,130(41):13592-13610
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