Total synthesis of the indolizidine alkaloid tashiromine

• Stephen P. Marsden and
• Alison D. McElhinney

Beilstein J. Org. Chem. 2008, 4, No. 8, doi:10.1186/1860-5397-4-8

• the resulting carbonyl function and the amide. In the event, attempts to form a C5 aldehyde using either ozonolytic or dihydroxylation/periodate alkene cleavage protocols were unsuccessful, with complex mixtures being obtained in both cases. We suspected that the problem lay in the potential for the

An asymmetric synthesis of all stereoisomers of piclavines A1-4 using an iterative asymmetric dihydroxylation

• Yukako Saito,
• Naoki Okamoto and
• Hiroki Takahata

Beilstein J. Org. Chem. 2007, 3, No. 37, doi:10.1186/1860-5397-3-37

• dihydroxylation with enantiomeric enhancement. Background Indolizidine units are frequently found in many natural products and designed bioactive molecules. [1] Among these alkaloids, piclavines A1-4 (Figure 1), extracted from the tunicate Clavelina picta and the first indolizidine alkaloids to be found in the

• challenge. Our interest in this field has been focused on potential strategies based on the enantiomeric enhancement caused by the twofold or more application of the Sharpless asymmetric dihydroxylation (AD) [5][6] or Brown's asymmetric allylboration[7] reactions. In general, the enantiomeric excesses (ees

• all stereoisomers of piclavines A1-4 using an iterative asymmetric dihydroxylation. Experimental data which includes experimental details on the spectral instruments. Acknowledgements This work was supported in part by the High Technology Research Program from the Ministry of Education, Sciences

Single and double stereoselective fluorination of (E)-allylsilanes

• Marcin Sawicki,
• Angela Kwok,
• Matthew Tredwell and
• Véronique Gouverneur

Beilstein J. Org. Chem. 2007, 3, No. 34, doi:10.1186/1860-5397-3-34

• difluorinated alkene 7 (Scheme 4). The key steps necessary to perform this conversion were a dihydroxylation, the reduction of the ester group and the benzylation of the resulting primary alcohol. Preliminary work revealed that the order of steps was important and that protecting group manipulations were

• required for clean product outcome. The cis-dihydroxylation of 3 was performed employing NMO and catalytic OsO4 in DCM.[35] In the event, the diastereoselectivity was controlled by the two fluorine substituents. Four successful operations separated the newly formed unsymmetrical diol from 7, namely the

The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid

• Ishmael B. Masesane,
• Andrei S. Batsanov,
• Judith A. K. Howard,
• Raju Mondal and
• Patrick G. Steel

Beilstein J. Org. Chem. 2006, 2, No. 9, doi:10.1186/1860-5397-2-9

• . 3,4,5-Trihydroxy-2-aminocyclohexanecarboxylic acids The final group of targets we wished to generate was the trihydroxy analogs. Initial attempts addressed the generation of the syn 4,5 set. Consequently, OsO4 mediated dihydroxylation and subsequent peracylation of dienes 4 and 5 proved to be facio

• -specific and afforded cyclohexenyl derivatives 18 and 20 in 75 % yield over the two steps, Scheme 4. Reduction, as previously, afforded the trihydroxy β-aminoacid derivatives in excellent yields. At this stage it is instructive to address the interesting stereochemical outcome of this dihydroxylation

• reaction. Concurring with our results, Donohoe has reported that cyclic homoallylic carbamates give high levels of syn selectivity in the OsO4 mediated dihydroxylation reactions.[25][26] On the other hand, Kishi has established that the OsO4 mediated oxidation of cyclic allylic alcohols led preferentially

Synthesis and glycosidase inhibitory activity of new hexa- substituted C8-glycomimetics

• Olivia Andriuzzi,
• Christine Gravier-Pelletier,
• Gildas Bertho,
• Thierry Prangé and
• Yves Le Merrer

Beilstein J. Org. Chem. 2005, 1, No. 12, doi:10.1186/1860-5397-1-12

• enzymes. The synthesis of these new C8-glycomimetics is described from enantiomerically pure C2-symmetrical polyhydroxylated cyclooctenes. Their obtention notably involved a syn-dihydroxylation, and more extended functionalization through formation of a cis-cyclic sulfate followed by amination and

• cyclic double bond were explored to reach hexa-substituted C8-glycomimetics. Results and discussion From the C2-symmetrical L-ido- or D-manno- cyclooctene, 1 or 2, to obtain the C8 hexa-substitued carbasugars a straightfoward approach seemed to be a dihydroxylation, whereas to obtain the corresponding

• accomplished the synthesis of a range of new hexa-substituted C8-glycomimetics in enantiopure form. Transformation of the cyclic double bond involved syn-dihydroxylation, then introduction of an azido group by opening of a cyclic sulfate followed by reduction and eventual alkylation of the resulting amine

Methods for the synthesis of polyhydroxylated piperidines by diastereoselective dihydroxylation: Exploitation in the two-directional synthesis of aza-C-linked disaccharide derivatives

• Andrew Kennedy,
• Adam Nelson and
• Alexis Perry

Beilstein J. Org. Chem. 2005, 1, No. 2, doi:10.1186/1860-5397-1-2

• these enzymes. Results The scope, limitations and diastereoselectivity of the dihydroxylation of stereoisomeric 2-butyl-1-(toluene-4-sulfonyl)-1,2,3,6-tetrahydro-pyridin-3-ols is discussed. In the absence of a 6-substituent on the piperidine ring, the Upjohn (cat. OsO4, NMO, acetone-water) and Donohoe

• corresponding difuran. Selective substitution of its N,O acetal was possible. The stereochemical outcome of a two-directional Luche reduction step was different in the two heterocyclic rings, and depended on the conformation of the ring. Finally, two-directional diastereoselective dihydroxylation yielded seven

• paper, the final products are labelled according the configuration of the piperidine (A-D) and tetrahydropyran (d, d' or e) ring systems. Note that the ring systems d and d' are enantiomeric.) Results and discussion Synthesis of substrates for model dihydroxylation reactions Methods for the