Ferdinand Belaj

Regio- and stereoselective monoamination of diketones without protecting groups.

) out of six showed perfect regioselectivity forthe differentiation between the two keto groups. Hence, theamination occurred exclusively at the sterically less demand-ing w-1 ketone moiety, leading to the amino ketone 2a, whilethe w-3 position remained untouched. The intermediateamino ketone 2aspontaneously cyclized, finally giving D1-piperideine 4a. Only the w-TA from Vibrio fluvialis

Novel Pyridazine Based Scorpionate Ligands in Cobalt and Nickel Boratrane Compounds

Heating of 6-methylpyridazine-3-thione (HPn(Me)) and 6-tert-butylpyridazine-3-thione (HPn(tBu)) with potassium borohydride in diphenylmethane in a 3:1 ratio gave two new scorpionate ligands K[HB(Pn(Me))(3)] and K[HB(Pn(tBu))(3)]. Single crystal X-ray diffraction analysis of the methyl derivative K[HB(Pn(Me))(3)] revealed a dimeric species with one potassium atom coordinated by six sulfur atoms of two scorpionate ligands and a second potassium atom coordinated by three nitrogen atoms of one of the two ligands as well as by three water molecules. The reaction of K[HB(Pn(tBu))(3)] with nickel(II) chloride or cobalt(II) chloride in CH(2)Cl(2) led to the new boratrane compounds [M{B(Pn(tBu))(3)}Cl] (M = Ni 1, Co 3) where a formal reduction of the metal ions to Ni(I) and Co(I), respectively, and activation of the B-H bond occurred. Similar reactivity was observed by employing K[HB(Pn(R))(3)] (R = Me, tBu) and nickel(II) chloride in water. Reaction with cobalt(II) chloride in water also gave boratrane compounds [Co{B(Pn(R))(3)}(Pn(R))] (R = tBu 4, Ph 5), but instead of a chloride a bidentate pyridazinethionate ligand from a defragmentated scorpionate is found in the molecules. The molecular structures of all nickel and cobalt compounds were determined by single crystal X-ray diffraction analyses confirming the formation of boratranes in compounds 1-5. Magnetic measurements confirm the reduced oxidation states and the paramagnetic character of the Ni(I) and Co(I) complexes. Supportive DFT studies were carried out for a better understanding of the electronic nature of the metal-boron bond of the boratrane complexes.

Dioxomolybdenum(VI) Complexes with Pyrazole Based Aryloxide Ligands: Synthesis, Characterization and Application in Epoxidation of Olefins

Synthesis, characterization, and epoxidation chemistry of four new dioxomolybdenum(VI) complexes [MoO(2)(L)(2)] (1-4) with aryloxide-pyrazole ligands L = L1-L4 is described. Catalysts 1-4 are air and moisture stable and easy to synthesize in only three steps in good yields. All four complexes are coordinated by the two bidentate ligands in an asymmetric fashion with one phenoxide and one pyrazole being trans to oxo atoms, respectively. This is in contrast to the structure found for the related aryloxide-oxazoline coordinated Mo(VI) dioxo complex 5. This was confirmed by the determination of the molecular structures of complexes 1-3 by X-ray diffraction analyses. Compounds 1-4 show high catalytic activities in the epoxidation of various olefins. Cyclooctene (S1) is converted to its epoxide with high activity, whereas the epoxidation of styrene (S2) is unselective. Internal olefins (S3 and S4) are also acceptable substrates, as well as the very challenging olefin 1-octene (S5). Catalyst loading can be reduced to 0.02 mol % and the catalyst can be recycled up to ten times without significant loss of activity. Supportive DFT calculations have been carried out in order to obtain deeper insights into the electronic situation around the Mo atom.

Oxo-molybdenum and oxo-tungsten complexes of Schiff bases relevant to molybdoenzymes

A series of octahedral dioxomolybdenum(VI) complexes of the type [MoO(2)L(2)] {L = 4-Ar-pent-2-en-ol; L(i-Pr2Ph) with Ar = 2,6-diisopropylphenyl (1); L(Me2Ph) with Ar = 2,6-dimethylphenyl (2), L(MePh) with Ar = 2-methylphenyl (3) and with Ar = phenyl (4)} and dioxotungsten(VI) compounds [WO(2)L(2)] {L(i-Pr2Ph) (5); L(Me2Ph) (6) and L(MePh) (7)} with Schiff bases have been synthesized as models for oxotransferases. Spectroscopic characterization in solution shows with the sterically encumbered ligands L(i-Pr2)Ph and L(Me2)Ph isomerically pure products whereas the ligand with only one substituent in ortho position at the aromatic ring L(MePh) revealed a dynamic mixture of three isomers as confirmed by variable temperature NMR spectroscopy. Single crystal X-ray diffraction analyses of compounds 1, 2, and 4 and showed them to be in the N,N-trans conformation consistent with the larger steric demand at nitrogen. Oxygen atom transfer (OAT) properties towards trimethylphosphine were investigated leading to the isolation of two mononuclear molybdenum(IV) compounds [MoO(PMe(3))(L(Me2Ph))(2)] (8) and [MoO(PMe(3))(L(MePh))(2)] (9) as confirmed by spectroscopic and crystallographic means. The kinetics of OAT between complex [MoO(2)(L(Me2Ph))(2)] (2) and PMe(3) was investigated by UV/Vis spectroscopy under pseudo-first-order conditions revealing single-step reactions with Eyring values of DeltaH(double dagger) = +60.79 kJ mol(-1) and DeltaS(double dagger) = -112 J mol(-1) K(-1) and a first-order dependence of phosphine consistent with a slow nucleophilic attack of the phosphine showing the octahedral geometries of this system to be unfavorable for OAT. Compound 1 showed no OAT reactivity towards PMe(3) emphasizing the influence of sterical properties. Furthermore, the reactivity of the reduced compounds [MoO(PMe(3))(L(Me2Ph))(2)] (8) and [MoO(PMe(3))(L(MePh))(2)] (9) towards molecular oxygen was investigated leading, in the case of 8, to the substitution of PMe(3) by O(2) under formation of the peroxo compound [MoO(O(2))(L(Me2Ph))(2)] (10). In contrast, the analogous reaction employing 9 led to oxidation forming the dioxo compound [MoO(2)(L(MePh))(2)] (3).

LONG-WAVELENGTH-ABSORBING AND -EMITTING CARBOSTYRILS WITH HIGH FLUORESCENCE QUANTUM YIELDS

Synthesis, absorption and fluorescence spectra, as well as quantum yields of a series of donor-acceptorsubstituted carbostyrils (a quinolin-2(1H )-ones), are reported. Unprecedented strong absorption maxima (ea 10000 ‐ 20000) close to the visible spectrum, large Stokes shifts up to 130 nm, and quantum yields up to 0.7 are obtained with derivatives containing donor substituents at C(6) and C(7), and either one Ph substituent at C(3) or one CF 3 residue at C(4). For analytical applications in biochemistry and medicine, N(1)-functionalization, or amidoacylation at C(3) in the case of the CF 3 derivatives, is possible without a concomitant hypsochromic shift of their absorption and emission maxima. Semiempirical molecular-orbital calculations ( AM1 for structures, ZINDO for electronic transition energies) prove to be a suitable tool for the prediction of absorption properties of these compounds. The crystal-structure analysis of 6,7-dimethoxy-1-methyl-3-nitro-4-(trifluoromethyl)quinolin-2-(1H )-one (7 )( C 13H11F 3N2O5, monoclinic, P21/c, aa 12.372(2), ba 12.154(2), ca 10.119(2)a, ba 112.95(2)8) shows that the NO2 group, squeezed between the CF 3 and the CaO group, is oriented almost perpendicularly (87.8(4)8) to the ring plane. The intramolecular F ··· N distance between the CF 3 and the NO2 group is only 2.513(4)a.

One-pot synthesis of 4-aminobicyclo[2.2.2]octan-2-ones

Abstract Dialkylammonium rhodanides and benzylidene acetone give racemic (6RS,7RS)-4-dialkylamino-bicyclo[2.2.2]octan-2-ones in a one-pot reaction in good yields. The mechanism of the reaction includes a Diels-Alder step. The structures are established by NMR spectra and a single crystal structure analysis. The compounds consist of cations of racemates of optically active (6R,7R)- and (6S,7S)-4-dialkylamino-6,7-diphenylbicyclo[2.2.2]octan-2-ones and isothiocyanate anions.

Synthesis of Methyl 2-Acetamido-2-deoxy-1-seleno-β-d-gluco- and galacto-pyranoside: Selenium Metabolites in Human Urine

An efficient synthesis of two methyl 2-acetamido-2-deoxy-1-seleno-β-d-hexopyranosides is reported. The synthesized compounds, which have recently been identified in human urine, will be used in further studies on the metabolism and toxicology of selenium.

Neat carbomethoxypivaloylketene—preparation and chemical reactivity

Abstract Neat carbomethoxypivaloylketene, the first fairly persistent α-oxoketene stabilized both electronically as well as sterically, is generated by flash vacuum pyrolysis of the corresponding furan-2,3-dione. It adds primary amines to afford pivaloyl-malonic acid amides and undergoes hetero-Diels–Alder reactions to furnish usual and unusual [4+2] adducts. Some stereo- and regiochemical features are verified with aid of 2D NMR experiments and a X-ray structure analysis.

Replacement of an Oxo by an Imido Group in Oxotransferase Model Compounds: Influence on the Oxygen Atom Transfer

Treatment of [MoO(N-t-Bu)Cl(2)(dme)] (dme = dimethoxyethane) with 2 equiv of the potassium salts of Schiff base ligands of the type KArNC(CH(3))CHC(CH(3))O afforded oxo imido molybdenum(VI) compounds [MoO(N-t-Bu)L(2)] {1, with Ar = phenyl (L(Ph)), 2 with Ar = 2-tolyl (L(MePh)), 3 with Ar = 2,6-dimethylphenyl (L(Me2Ph)) and 4 with Ar = 2,6-diisopropylphenyl (L(iPr2Ph))}. We have also prepared related bisimido complexes [Mo(N-t-Bu)(2)L(2) (5 with L = L(Ph), 6 with L = L(MePh), and 7 with L = L(Me2Ph)) by treatment of [Mo(N-t-Bu)(2)Cl(2)(dme)] with 2 equiv of the potassium salt of the respective ligand. 1, 3, 5, and 6 were characterized via single crystal X-ray diffraction. The oxo imido complexes exhibit oxygen atom transfer (OAT) reactivity toward trimethyl phosphine. Kinetic data were obtained for 1 and 3 by UV/vis spectroscopy revealing decreased OAT reactivity in comparison to related dioxo complexes with the same Schiff base ligands and decreased reactivity of 1 versus 3. Cyclic voltammetry was used to probe the electronic situation at the molybdenum center showing reversible reduction waves for 3 and [MoO(2)(L(Me2Ph))(2)] at comparable potentials while 1 exhibits a significant lower potential. Density functional theory (DFT) calculations showed a higher electron density on oxygen in the oxo imido complexes.

Dimeric μ-oxo bridged molybdenum(VI) dioxo complexes as catalysts in the epoxidation of internal and terminal alkenes

The preparation of the tridentate phenol based amine ligands HL1–HL4 is achieved via a convenient one-pot synthesis by reductive amination in quantitative yield in an autoclave under 7 bar H2 gas. Reaction of [MoO2(acac)2] and the corresponding ligand HLX (X = 1, 2 and 4) in methanol–H2O results in the formation of orange to red dimeric μ-oxo bridged [{MoO2(LX)}2(μ-O)] (X = 1, 2 and 4) complexes 1–3 in high yield and high purity. Complexes 1–3 are stable towards air and water. Both ligands coordinate via the phenolic O atom, the amine N atom and the third donor atom in the side chain (OMe for 1 and NMe2 for 2 and 3) in a fac mode to the metal center. The molybdenum atoms are linked by a bridging μ-oxo moiety to each other as confirmed by X-ray diffraction analyses of complexes 2 and 3. All complexes have been tested in the epoxidation of several internal and terminal alkenes using TBHP as an oxidant. Depending on the nature of the substrate, the epoxides are obtained in moderate to good yields and high selectivities. In the epoxidation of cyclooctene a TOF = 467 h−1 with complex 1 has been observed, significantly higher compared to other dimeric complexes reported in the literature. In the more challenging epoxidation of styrene, complexes 1 and 2 have proven to be highly selective as only the formation of styrene oxide is observed. The OMe based complex 1 has also proven to be more active than the NMe2 based counterparts 2 and 3. The basic conditions induced by the NMe2 groups in complexes 2 and 3 lower their catalytic activity.