Reactions of chiral phosphoramidites with complexes Pd(COD)Cl2 and Pt(COD)Cl2

Reactions of phosphoramidites based on (−)-ephedrine and [(1S)-endo]-(−)-borneol with the complexes M(COD)Cl₂ (M is Pd or Pt, and COD is cycloocta-1,5-diene) were studied. The formation ofcis andtrans complexes of the general formulas MCl₂L₂ and M₂Cl₂(μ-Cl)₂L₂ was observed. The structures of the resulting compounds were established by³¹P,¹³C, and¹⁹⁵Pt NMR and IR spectroscopy and by plasma desorption mass spectrometry. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1627–1630, August, 1998.     

Synthesis of l-α-phosphatidyl-d-myo-inositol 3,5-bisphosphate from d-glucose

Efficient synthesis of l-α-phosphatidyl-d-myo-inositol 3,5-bisphosphate was achieved from 1,2,5,6-diisopropylidene-d-glucose by utilizing ring-closing metathesis and catalytic OsO₄ dihydroxylation.     

The “Speedy” Synthesis of Atom‐Specific 15N Imino/Amido‐Labeled RNA

Although numerous reports on the synthesis of atom‐specific ¹⁵N‐labeled nucleosides exist, fast and facile access to the corresponding phosphoramidites for RNA solid‐phase synthesis is still lacking. This situation represents a severe bottleneck for NMR spectroscopic investigations on functional RNAs. Here, we present optimized procedures to speed up the synthesis of ¹⁵N(1) adenosine and ¹⁵N(1) guanosine amidites, which are the much needed counterparts of the more straightforward‐to‐achieve ¹⁵N(3) uridine and ¹⁵N(3) cytidine amidites in order to tap full potential of ¹H/¹⁵N/¹⁵N‐COSY experiments for directly monitoring individual Watson–Crick base pairs in RNA. Demonstrated for two preQ₁ riboswitch systems, we exemplify a versatile concept for individual base‐pair labeling in the analysis of conformationally flexible RNAs when competing structures and conformational dynamics are encountered.     

Novel BIPHEN H2 based P,S-bidentate phosphoramidite ligand in palladium-catalyzed asymmetric allylation

The reaction of P,S-phosphoramidite bearing (R_a)-BIPHEN H2 core and exocyclic amino sulfide as the new ligand with [Pd(ppp-allyl)Cl]₂ in the presence of AgBF₄ yielded a cationic metallochelate [Pd(ppp-allyl)(L)]BF₄. This new chiral inducer provided up to 90% ee in the Pd-mediated allylic substitution reaction of (E)-1,3-diphenylallyl acetate with various C- and N-nucleophiles. In the Pd-catalyzed amination of 2-diethoxyphosphoryl-1-phenylallyl acetate with aniline, ee values up to 57% were achieved.     

The Usefulness of Trivalent Phosphorus for the Synthesis of Dendrimers

Dendrimers are hyperbranched macromolecules, which are synthesized step-by-step by the repetition of a series of reactions. While many different types of dendrimers are known, this review focusses on the use of trivalent phosphorus derivatives (essentially phosphines and phosphoramidites) for the synthesis of dendrimers. The first part presents dendrimers constituted of phosphines at each branching point. The other parts display the use of trivalent phosphorus derivatives during the synthesis of dendrimers. Different types of reactions have been applied to phosphines. The very first examples of phosphorus-containing dendrimers were obtained by the alkylation of phosphines. Then, several families of dendrimers were elaborated by reaction of phosphoramidites. Such a type of reaction is the base of the solid phase synthesis of oligonucleotides; it has been applied in particular for the synthesis of dendrimers constituted of oligonucleotides. Finally, the Staudinger reaction between phosphines and azides afforded different families of dendrimers, and was at the origin of accelerated methods of synthesis of dendrimers. Besides, the reactivity of the P=N-P=S linkages created by this reaction led to very original dendritic structures.     

A Striking Case of Enantioinversion in Gold Catalysis and Its Probable Origins

The cyclization of the hydroxy‐allene 2 to the tetrahydrofuran 3 catalyzed by the gold‐phosphoramidite complex 1 , after ionization with an appropriate silver salt AgX, is one of the most striking cases of enantioinversion known to date. The major reason why the sense of induction can be switched from (S) to (R) solely by changing either the solvent or the temperature or the nature of the counterion X is likely found in the bias of the organogold intermediates to undergo assisted proto‐deauration. Such assistance can be provided by a protic solvent, a reasonably coordinating counterion or even by a second substrate molecule itself; in this case, the reaction free energy profile gains a strong entropic component that can ultimately dictate the stereochemical course.     

Preparation of 2,4-disubstituted cyclopentenones by enantioselective iridium-catalyzed allylic alkylation: synthesis of 2'-methylcarbovir and TEI-9826

A broadly applicable synthesis of chiral 2- or 2,4-substituted cyclopent-2-enones has been developed by combining asymmetric iridium-catalyzed allylic alkylation reactions and ruthenium-catalyzed ring-closing metathesis. Enantiomeric excesses (ee values) in the range of 95-99 % ee have been achieved. This method offers a straightforward access to biologically active prostaglandins of the PGA type. As an example, an enantioselective synthesis of the prostaglandin-analogue 13,14-dihydro-15-deoxy-Delta(7)-prostaglandin-A1-methyl ester (TEI-9826) has been carried out. Furthermore, the carbonucleoside 2'-methylcarbovir has been prepared from O-protected 4-hydroxymethyl-2-methyl-cyclopent-2-enone by Pd-catalyzed allylic amination.