Gunadi Adiwidjaja

Reactions of thioketen s-oxides with diazo compounds : A novel synthesis of heterocyclic sulfines

Abstract Thioketen S-oxides 1 react with 2-diazopropane (2a) to give 1-pyrazoline-4-thione S-oxides 3 Addition of diazomethane to 1 yields a stable 1:1-adduct only from the S-oxide 1c. The constitution of both types of cycloadducts (3, 11) was proven by X-ray diffraction. Irradiation of 3 leads to loss of nitrogen to afford the alkylidene thiirane S-oxides 12.

CYCLIZATION OF DEPROTONATED 2-PHENYL-1-TOSYLAZIRIDINE. A SURPRISING EXAMPLE OF AN INTRAMOLECULAR NUCLEOPHILIC AROMATIC ADDITION

Abstract Deprotonation of 2-phenyl-1-tosylaziridine 1 with butyl lithium gives an anion that cyclizes to 4 by an intramolecular nucleophilic aromatic addition. Treatment of derivatives 5, 6 with a Grignard reagent produces aziridines 10, 11 .

Aufklärung der 1H- und 13C-NMR-spektren sowie der kristallstruktur ungesättigter glycosylphosphonate und konformationsberechnungen an modellen

Zusammenfassung Die Anwendung eines modifizierten LAOCN-3 Programms fuhrt zur vollstandigen Aufklarung der 1 H-NMR-Spektren der 2,3-ungesattigten Glycosylphosphonate 1–5 . Die erstmalig exakt bestimmten n J(H, H)- und neuartigen n J(H, P)-Kopplungsparameter werden diskutiert und lassen Ruckschlusse auf die Konformation zu. Von allen Verbindungen werden vollstandig interpretierbare 13 C-NMR-Spektren erhalten. Die Diskussion der chemischen Verschiebungen sowie der 1 J(C-H)- und der n J(C,P)-Kopplungskonstanten stutzt die konformativen Zuordnungen. An allen Derivaten konnen die Beziehungen 1 J(C-1, H e ) > 1 J(C-1, H a ) und 1 J(C-1, P e ) > 1 J(C-1, P a ) fur die Anomerenzuordnung Verwendung finden. Die Kristallstrukturanalyse von 1 steht in Ubereinstimmung mit der Anomerenzuordnung und ergibt eine nicht erwartete Konformation. MINDO-3 Berechnungen an Modellen dienen der Erlauterung derartiger konformativer Effekte.

Synthesis and Structural Elucidation of 2′‐Deoxy‐4′‐thio‐L‐threo‐pentofuranosylpyrimidine and ‐purine Nucleosides

Benzyl 3,5-di-O-benzyl-2-deoxy-1,4-dithio-L-threo-pentofuranoside (13) was used as glycosyl donor for the synthesis of 4′-thio-L-threo-pentofuranosyluracil derivatives 23−29. The corresponding cytidine analogue 33 was prepared from 13 via the triazolo derivative 31. Adenine and hypoxanthine did not react with 13. Therefore, 13 was transformed into the 1-O-acetate 15, which was a sufficiently reactive donor for the purine bases, yielding 4′-thio-L-threo-pentofuranosylpurines 36 and 37. In most cases it was possible to obtain pure anomers of the deprotected nucleoside analogues, three of which were suitable for X-ray structural analyses.

Preparation of selenoanhydro- and telluroanhydroglycofuranosides and some corresponding nucleosides.

Methyl 2,3-anhydro-alpha-D-ribofuranoside (3a) was transformed into methyl 2-seleno-2,5-anhydro-alpha-D-arabinofuranoside (5a) and methyl 3-seleno-3,5-anhydro-alpha-D-xylofuranoside (6a) in two steps via the reaction of the C-5 mesylate of 3a, methyl 2,3-anhydro-5-O-mesyl-alpha-D-ribofuranoside (4a), with sodium hydrogen selenide. The corresponding beta anomer of 3a yielded methyl 3-seleno-3,5-anhydro-beta-D-xylofuranoside as the main product and only traces of methyl 2-seleno-2,5-anhydro-beta-D-arabinofuranoside. Sodium hydrogen telluride transformed 4a into methyl 2-telluro-2,5-anhydro-alpha-D-arabinofuranoside. Starting from 5a we prepared 1-(2-seleno-2,5-anhydro-alpha-D-arabinofuranosyl)uracil and the analogous thymidine nucleoside. Compound 6a could not be transformed into nucleosides.

Thiosugars. Part 9: Synthesis and Biological Evaluation of Some 4′-Thio-l-arabino Nucleoside Analogues ☆

1-O-Acetyl-2,3,5-tri-O-benzyl-4-thio-L-arabinofuranose (10) was transformed into the corresponding cytidine derivative 9 and the adenosine derivative 12. Both nucleosides, as well as the previously reported uridine and thymidine analogues 2 and 3, were tested for their in vitro antiviral activity.

Cyclizations of 5-silyl-substituted 4,5-epoxy-1-alkanols: A configuration dependent mode of ring closure

Abstract The preparation and proton-induced cyclization of silyl-substituted 4,S-epoxy-l-alkanols is described The regioselectivity of intramolecular attack of the hydroxy group on the epoxy silane moiety is highly dependent on the configuration of the epoxy alcohols employed. Thus 1,4-anti epoxy alcohols exclusively yield tetrahydropyrans whereas the corresponding 1,4-syn derivates furnish a diastereomeric mixture of tetrahydrofurans.

4-thioxo-2-azetidinones by cycloaddition of thioketenes with isocyanates

Abstract The (2+2) cycloaddition of thioketenes 1 with isocyanates 2 yields 4-thioxo-2-azetidinones 3 , which can be hydrolyzed to the N-unsubstituted compound 4 and thus used as versatile intermediates.

Preparation of methyl 2,3-di-O-mesyl-4,6-thioanhydro-α-d-galactopyranoside and methyl 2-O-mesyl-4,6-thioanhydro-α-d-gulopyranoside

Abstract Two 2-oxa-7-thiabicyclo[4.2.0]octane derivatives, 4 and 10, with the d -galacto and d -gulo configuration, respectively, were obtained from methyl α- d -glucopyranoside. The thietane cyclization involved a thio-Mitsunobu reaction resulting in a 6-thioacetate, which underwent selective base-catalyzed intramolecular nucleophilic substitution at a C-4 mesylate. The structureS of 4 and 10 were elucidated by X-ray diffraction analysis.

FACILE SYNTHESIS OF ENANTIOMERICALLY PURE TERT-BUTYL(METHYL)PHENYLSILANES

Abstract A method for the preparation of both enantiomers of tert-butyl(methyl)phenylsilane 2 is presented. Racemic tert-butyl(methyl)phenylsilyl chloride 3 was allowed to react with (R)-(−)-2-amino-1-butanol 4 to give hydrochloride 5. Diastereomer separation via treatment of the respective free amine 6 with 0.5 mol equivalent of HCl in hexane-2-propanol yielded crystalline diastereomerically pure hydrochloride (R)Si-5. The corresponding free amine (R)Si-6 was reduced with LiAlH4 to give (S)-2. The mother liquors obtained after separation of (R)Si-5 on treatment with oxalic acid provided a crystalline salt that eventually afforded (R)-2. The optical purity of (S)-2 (98% ee) was documented by its reaction (hydrosilylation) with propargylic alcohol derivative 10 and HPLC analysis of product 11 using a chiral column.