Synthese von Trifluoromethyl-substituierten Schwefel-Heterocyclen unter Verwendung von 3,3,3-Trifluorobrenztraubensäure-Derivaten

Synthesis of Trifluoromethyl-Substituted Sulfur Heterocycles Using 3,3,3-Trifluoropyruvic-Acid Derivatives The reaction of methyl 3,3,3-trifluoropyruvate ( 1 ) with 2,5-dihydro-1,3,4-thiadiazoles 4a, b in benzene at 45° yielded the corresponding methyl 5-(trifluoromethyl)-1,3-oxathiolane-5-carboxylates 5a, b (Scheme 1) via a regioselective 1,3-dipolar cycloaddition of an intermediate ‘thiocarbonyl ylide’ of type 3 . With methyl pyruvate, 4a reacted similarly to give 6 in good yield. Methyl 2-diazo-3,3,3-trifluoropropanoate ( 2 ) and thiobenzophenone ( 7a ) in toluene underwent a reaction at 50°; the only product detected in the reaction mixture was thiirane 8a (Scheme 2). With the less reactive thiocarbonyl compounds 9H-xanthene-9-thione ( 7b ) and 9H-thioxanthene-9-thione ( 7c ) as well as with 1,3-thiazole-5(4H)-thione 12 , diazo compound 2 reacted only in the presence of catalytic amounts of Rh₂(OAc)₄. In the cases of 7a and 7b , thiiranes 8b and 8c , respectively, were the sole products (Scheme 3). The crystal struture of 8c has been established by X-ray crystallography (Fig.). In the reaction with 12 , desulfurization of the primarily formed thiirane 14 gave the methyl 3,3,3-trifluoro-2-(4,5-dihydro-1,3-thiazol-5-ylidene)propanoates (E)-and (Z)- 15 (Scheme 4). A mechanism of the Rh-catalyzed reaction via a carbene addition to the thiocarbonyl S-atom is proposed in Scheme 5.     

Synthese von Triafulven-Vorstufen aus trisubstituierten Cyclopropanen

Synthesis of Triafulvene-Precursors from Trisubstituted Cyclopropanes Trisubstituted cyclopropanes 5a–f are prepared by carbene addition to the appropriate olefins. While 5a (Y = OAc) and 5c (Y = Cl) rearrange in the presence of BuLi, 5d (Y = SPh) is stable enough to allow the envisaged sequence for triafulvene (Scheme 2) : halogen-Li exchange, followed by methylation of 6d , gives 7d in a 93% yield; after base-induced elimination of HB r from 7d , the key precursor 1-methylene-2-(phenylthio)cyclopropane ( 9 , 70% yield) is isolated. Compound 9 is transformed into the corresponding sulfoxide 10 (83%), sulfone 11 (80%), and sulfonium fluoroborate 12 (95% yield) by subsequent oxidation and methylation, respectively. Some ¹H-NMR results of cyclopropanes 5a–f and 7d as well as of methylidene-cyclopropanes 9–11 are discussed.     

Stereoselektive Synthese von Pyrrolizidin-Alkaloiden aus Nitroalkanonen

Stereoselective Synthesis von Pyrrolizidin Alkaloids from Nitroalkanones Reduction of 5-nitropentadecane-2,8-dione ( 11 ), synthesized by a Michael reaction from nitromethane, methyl vinyl ketone, and dec-1-en-3-one, gave, depending on the conditions, two epimeric 3-heptyl-2,3,5,6,7,7a-hexahydro-5-methyl-1H-pyrrolizines as the main products: Catalytic hydrogenation (Pd/C) afforded the expected 7aα-hydro epimer 1b with cis-orieted H-atoms at C(3), C(5), and C(7a). NaBH₃CN/NH₄OAc reduction of the nitrodione 11 yielded all four diastereoisomers with the 7aβ-hydro epimer 1a as the predominant component; 1a is a pheromone of the cryptic thief ant Solenopsis sp. The N-atom of the pyrrolizidine ring stems from NH₄OAc exclusively as shown by reduction of 11 with NaBH₃CN/(¹⁵N)H₄OAc.     

Synthese von Indolen und Isochinolonen aus Phenylmalonylheterocyclen

A new synthesis of the indole system has been achieved by chclodehydrogenation of amino phenylmalonate heterocycles. Thus, the 4-amino coumarins1 a,b or the 4-amino-2-quinolones1 c–g are converted to the indoles2 with palladium on charcoal in boiling diphenyl ether. The reaction of the aminocompounds1 with diphenyl carbonate yields the fused polycyclic isoquinolones4.

     

Synthese von Nucleosiden aus 2-substituierten Imidazolen

Synthesis of 2-Substituted Imidazole Nucleosides Condensation of the trimethylsilyl derivatives of 2-substituted diethyl and dimethyl imidazole-4,5-dicarboxylates ( 3–5 and 7–9 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D -ribofuranose ( 2 ) in the presence of trimethysilyl trifluoromethanesulfonate provided the 2-substituted diethyl and dimethyl 1-(2′,3′, 5′-tri-O-benzoyl-β-D -ribofuranosyl)imidazole-4, 5-dicarboxylates 10–15 . These were treated with ammonia to afford the 2-substituted 1-(β-D -ribofuranosyl)imidazole-4,5-dicarboxamides 16–21 . Treatment of 2-methyl-( 16 ) and 2-ethyl-1-(β-D -ribofuranosyl)imidazole-4,5-dicarboxamide ( 17 ) with fuming nitric acid in oleum at ?30° yielded the nitric acid esters 23 and 24 . Besides the esterification of the sugar hydroxyl groups one H-atom of the imidazolecarboxamide function at C(5) in these nucleosides was also substituted by the NO₂ group. The conformations in solution of 16 and 23 have been determined by ¹H- and ¹³C-NMR. spectroscopy. These studies indicate that the nucleosides exist in dimethyl-sulfoxide solution preferentially in the S-gg-syn-conformation ( 16 ) and N-gt-conformation ( 23 ). In the crystal structure of nucleoside 23 , the ribose was found to be in the O(1′)_endo, C(1′)_exo twist conformation. The conformation about C(4′), C(5′) is gauche-trans and the molecule exists in the syn form.     

Synthese von Polythioamiden aus Dithioamid und Diamin

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