2, 3-Alkadiensäureester als Dienophile; Anwendung bei der Synthese von (+)-(R)-Lasiodiplodin

2,3-Alkadienoates as Dienophiles, Application in the Synthesis of (+)-(R)-Lasiodiplodin Methyl 2, 3-alkadienoates 2 are shown to react at 80° with l, 1-dimethoxy-3trimethylsilyloxy-l, 3-butadiene (1) to give the adducts 3 in good yields. Rearrangement of 3 , catalyzed by p-toluenesulfonic acid or by sodium methoxide, affords the 6-substituted methyl 4-hydroxy-2-methoxybenzoates 4 (R ? H, CH₃, C₆H₅). An analogous reaction sequence starting with (-)-(11 R)-dodeca-2, 3-dien-11-olide ((-) -6 ) and 1 leads, via the adduct (R)-7 , to (+)-( R )-lasiodiplodin ((+) ?8 ) with properties identical to those of the natural product. The allene lactone (-) -6 was prepared by an intramolecular Wittig condensation of (R) ?5 , produced from (–)-(R)-9-hydroxydecanoic acid.     

Isolierung,Konstitution und Synthese der (R)-(−)-Eucominsäure

From the bulbs of Eucomis punctata L'Hérit. (Liliaceae) and of a hitherto undefined species of Eucomis a new optically active phenolic carboxylic acid, eucomic acid, was isolated. Structure 1 was assigned on the basis of chemical and spectral evidence. The absolute configuration of eucomic acid was determined by its correlation with piscidic acid ((2 R, 3 S)-2-(4′-hydroxybenzyl)-tartaric acid) ( 8 ). Consequently, eucomic acid is (R)-(?)-2-(4′-hydroxybenzyl)-malic acid ( 1 ). For the stereospecific synthesis, methyl cis-p-methoxybenzylidene-succinic acid ( 22 ) was transformed into the γ-lactone 24 which, by catalytic hydrogenolysis, yielded (±)-2-(4′-hydroxybenzyl)-malic acid 1-methyl ester ( 27 ). Resolution with (?)-quinine led to the enantiomeric acids 29 and 30 . The methyl ester of the levorotatory enantiomer 30 was identical with the dimethyl ester 3 of 4′-O-methyl-eucomic acid.     

Michael-Addition von Thiocarbonsäureestern Anwendung bei der Synthese von (±)-Jasminketolacton

Michael addition of carbothioates. Application to the synthesis of (±)-jasmine ketolactone It is shown that the lithium enolate of S-t-butyl thioacetate adds to 2-cyclopentenone in the β-position and that fluoride ions catalyze the 1, 4-addition of the trimethylsilyl enol ether of S-t-butyl thioacetate ( 5 ) to 2-cyclopentenone ( 4 ) to give 6 . These novel versions of the Michael addition have been applied to a synthesis of jasmonoid compounds. Cleavage of the trimethylsilyl enol ether in 6 with tetrabutylammonium fluoride produced the corresponding ketone enolate which could be trapped in situ by alkylation with 1-bromo-5-(2′-tetrahydropyranoxy)-2-pentyne ( 7 ) to form 8 . Removal of the alcohol protecting group in 8 , followed by partial hydrogenation of the triple bond over Lindlar palladium and mercury ion promoted hydrolysis of the carbothioate moiety in 9 , led to 5′-hydroxy jasmonic acid ( 10 , Scheme 3). 10 was converted into the S-(2-pyridyl) carbothioate and cyclized in dilute benzene solution under the influence of silver ion to give (±)-jasmine ketolactone ( 1 , Scheme 4), a component of the essential oil of Jasminum grandiflorum, in 72% yield. Similarly, methyljasmonate ( 2 , Scheme 2) was obtained from 6 by the reaction with 1-bromo-2-pentyne and tetrabutylammonium fluoride followed by methanolysis and partial hydrogenation of the triple bond.     

Synthese von (−)-(R)-Nephthenol und (−)-(R)-Cembren A

Synthesis of (?)-(R)-Nephthenol and (?)-(R)-Cembren A Starting for L -serine,(?)-(R)-nephthenol((?)- 2 ) and (?)-(R)-cembren A((?)- 3 ) were synthesized.     

Synthese und Struktur des Kupferkomplexes 2-(2-Hydroxy-5-methylphenyl)-6-(2-hydroxyphenyl)pyridinato(2−)-dipyridin-kupfer(II) und des freien Liganden

Synthesis and Structure of the Copper Complex 2-(2-Hydroxy-5-methylphenyl)-6-(2-hydroxyphenyl)pyridinato(2?)dipyridin-copper(II) and of the free Ligand The tridentate diacidic ligand 2-(2-hydroxy-5-methyl)-6-phenyl-6-(2-hydroxyphenyl)pyridine 4a was synthesized and characterized by X-ray structural analysis. The compound forms a copper complex, 2-(2-Hydroxy-5-methyl-phenyl)-6-(2-hydroxyphenyl)pyridinato(2?)-dipyridine copper(II), which was crystallized from pyridine solution. The coordination number of the central atom copper ist five.     

Über die Anwendung von Lanthaniden-Verschiebungs-Reagenzien (LSR) bei der Strukturbestimmung flexibler Moleküle,am Beispiel des 2-Methyltetrahydropyrans und des cis-4-Methyl-2-(2′-methyl-1′-propenyl)- tetrahydropyrans

The model of Davis and Willcott can be successfully applied to ¹H NMR lanthanide induced shifts (LIS) of 2-methyltetrahydropyran in the presence of Eu(dpm)₃. By contrast, the model does not work in the case of cis-4-methyl-2-(2′-methyl-1′-propenyl)tetrahydropyran (cis-Rosenoxide), probably due to the presence of more than one LSR-substrate complex in the solution.     

Neue Synthese von (−)-(R)-Cembren A,Synthese von (+)-(R)-Cembrenen und (+)-(S)-Cembren

Novel Synthesis of (?)-(R)-Cembrene A, Synthesis of (+)-(R)-Cembrenene and (+)-(S)-Cembrene A novel synthesis of (?)-(R)-cembrene A ((?)- 3 ) was developed using the Sharpless epoxidation for the introduction of the chiral center. Furthermore, the synthesis of (+)-(R)-cembrenene ((+)- 4 ) showed that this cembranoid must have the (R)-configuration and not, as previously reported, the (S)-configuration. Selective hydrogenation of (+)- 4 afforded (+)-(S)-cenibrene ((+)- 5 ).     

Synthèse énantiospécifique des acides (+)-(2R)- et (−)-(2S)-éthyl-6-dihydro-3,4-méthyl-2-oxo-4–2H pyranecarboxylique-5

Enantiospecific Synthesis of (+)-(2R)- and (?)-(2S)-6-Ethyl-3,4-dihydro-2-methyl-4-oxo-2H-pyran-5-carboxylic Acid The two enantiomers (?)-(2S)- and (+)-(2R)-6-ethyl-3,4-dihydro-2-methyl-4-oxo-2H-pyran-5-carboxylic acid ((S)- and (R)- 7 ) have been synthesized from (+)-(3S) and (?)-(3R)-3-hydroxybutanoates, respectively (Scheme 1). By reduction and decarboxylation, the tetrahydro-2H-pyranols (2R, 4R, 6S)- and (2S, 4S, 6R)- 13 , respectively, were obtained with an enantiomeric excess of ≥ 93%.     

Synthese des Makrolid-Antibiotikums (−)-A26771B mit Photolactonisierung als Schlüsselreaktion und Computersimulation als effektive Optimierungshilfe

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.