Synthesis of Phosphorodiamidate Oligonucleotide Dimers.

Azido nucleosides couple with phosphoramidites via an initial iminophosphorane, which eliminates acrylonitrile to generate the coupled dimer P(V) product. The vulnerable phosphite triester intermediate is bypassed entirely, making the methodology very suitable to solution-phase synthesis. This new coupling protocol requires no protection of the 5'-OH function and provides a new method of installing internucleosidic phosphorodiamidate bonds with near quantitative yields.

Sulphide as a leaving group: highly stereoselective bromination of alkyl phenyl sulphides.

A conceptionally novel nucleophilic substitution approach to synthetically important alkyl bromides is presented. Using molecular bromine (Br2), readily available secondary benzyl and tertiary alkyl phenyl sulphides are converted into the corresponding bromides under exceptionally mild, acid- and base-free reaction conditions. This simple transformation allows the isolation of elimination sensitive benzylic ß-bromo carbonyl and nitrile compounds in mostly high yields and purities. Remarkably, protic functionalities such as acids and alcohols are tolerated. Enantioenriched benzylic ß-sulphido esters, readily prepared by asymmetric sulpha-Michael addition, produce the corresponding inverted bromides with high stereoselectivities, approaching complete enantiospecificity at -40 °C. Significantly, the reported benzylic ß-bromo esters can be stored without racemisation for prolonged periods at -20 °C. Their synthetic potential was demonstrated by the one-pot preparation of γ-azido alcohol (S)-5 in 90% ee. NMR studies revealed an initial formation of a sulphide bromine adduct, which in turn is in equilibrium with a postulated dibromosulphurane intermediate that undergoes C-Br bond formation.

Desulfurative Chlorination of Alkyl Phenyl Sulfides.

The chlorination of readily available secondary and tertiary alkyl phenyl sulfides using (dichloroiodo)benzene (PhICl2) is reported. This mild and rapid nucleophilic chlorination is extended to sulfa-Michael derived sulfides, affording elimination-sensitive ß-chloro carbonyl and nitro compounds in good yields. The chlorination of enantioenriched benzylic sulfides to the corresponding inverted chlorides proceeds with high stereospecificity, thus providing a formal entry into enantioenriched chloro-Michael adducts. A mechanism implying the formation of a dichloro-λ4-sulfurane intermediate is proposed.

Synthesis and coordination chemistry of a new N4-polydentate class of pyridyl-functionalized scorpionate ligands: complexes of Fe(II), Zn(II), Ni(II), V(IV), Pd(II) and use for heterobimetallic systems.

The new potentially N(4)-multidentate pyridyl-functionalized scorpionates 4-((tris-2,2,2-(pyrazol-1-yl)ethoxy)methyl)pyridine (TpmPy, (1)) and 4-((tris-2,2,2-(3-phenylpyrazol-1-yl)ethoxy)methyl)pyridine (TpmPy(Ph), (2)) have been synthesized and their coordination behavior toward Fe(II), Ni(II), Zn(II), Cu(II), Pd(II), and V(III) centers has been studied. Reaction of (1) with Fe(BF(4))(2) x 6 H(2)O yields [Fe(TpmPy)(2)](BF(4))(2) (3), that, in the solid state, shows the sandwich structure with trihapto ligand coordination via the pyrazolyl arms, and is completely low spin (LS) until 400 K. Reactions of 2 equiv of (1) or (2) with Zn(II) or Ni(II) chlorides give the corresponding metal complexes with general formula [MCl(2)(TpmPy*)(2)] (M = Zn, Ni; TpmPy* = TpmPy, TpmPy(Ph)) (4-7) where the ligand is able to coordinate through either the pyrazolyl rings (in case of [Ni(TpmPy)(2)]Cl(2) (5)) or the pyridyl-side (for [ZnCl(2)(TpmPy)(2)] (4), [ZnCl(2)(TpmPy(Ph))(2)] (6) and [NiCl(2)(TpmPy(Ph))(2)] (7)). The reaction of (1) with VCl(3) gives [VOCl(2)(TpmPy)] (8) that shows the N(3)-pyrazolyl coordination-mode. Moreover, (1) and (2) react with cis-[PdCl(2)(CH(3)CN)(2)] to give the disubstituted complexes [PdCl(2)(TpmPy)(2)] (9) and [PdCl(2)(TpmPy(Ph))(2)] (10), respectively, bearing the scorpionate coordinated via the pyridyl group. Compounds (9) and (10) react with Fe(BF(4))(2) to give the heterobimetallic Pd/Fe systems [PdCl(2)(mu-TpmPy)(2)Fe](BF(4))(2) (11) and [PdCl(2)(mu-TpmPy(Ph))(2)Fe(2)(H(2)O)(6)](BF(4))(4) (13), respectively. Compound (11) can also be formed from reaction of (3) with cis-[PdCl(2)(CH(3)CN)(2)], while reaction of (3) with Cu(NO(3))(2) x 2.5 H(2)O generates [Fe(mu-TpmPy)(2)Cu(NO(3))(2)](BF(4))(2) (12), confirming the multidentate ability of the new chelating ligands. The X-ray diffraction analyses of compounds (1), (3), (4), (5), and (9) are also reported.