High 1,5-anti stereoinduction in boron-mediated aldol reactions of methyl ketones.

[reaction: see text] We report herein a very efficient and synthetically useful 1,4-anti-1,5-anti boron-mediated aldol reaction of a chiral alpha-methyl-beta-alkoxy methyl ketone with achiral aldehydes.

Molecular structure of the molybdenum oxo-diperoxo compound MoO(O(2))(2)(OPy)(H(2)O): a computational and X-ray study.

We have carried out a combined experimental and theoretical study of the molecular structure of the MoO(O(2))(2)(OPy)(H(2)O) coordination compound using X-ray crystallography and DFT-B3LYP computational method, respectively. The MoO(O(2))(2)(OPy)(H(2)O) complex crystallizes in the orthorhombic space group Pmna with Z = 4, a = 6.9001(9) A, b = 8.0471(1) A, c = 16.227(2) A, V = 901.0(2) A(3), and the X-ray data analysis yields a bipyramidal-pentagonal coordination polyhedron for the Mo atom. The pyridine N-oxide (OPy) ligand occupies the equatorial position, with the oxygen atom of this ligand being located in the same plane as the four peroxo oxygen atoms. The H(2)O ligand is situated trans to the oxo group, forming intermolecular hydrogen bonds with peroxo groups belonging to two adjacent complexes. In our theoretical approach these intermolecular interactions were taken into account by including two methanol molecules which form hydrogen bonds with the water ligand leading to a good agreement between the calculated and the experimental geometry. Our results suggest that it is necessary to take into account the presence of these interactions in order to reconcile the theoretical results to the experimental data, in particular the distance between Mo and the oxygen of water ligand. These results seem to be a general feature for analogous bis-peroxo complexes that have been reported in the literature.

Two intermediates in the synthesis of decahydroisoquinolines with NMDA and AMPA receptor antagonist activity.

In 6-methyl-N-(4-nitrobenzoyl)-5,6-dihydropyridin-2(1H)-one, C(13)H(12)N(2)O(4), (I), the piperidone ring is in a distorted half-chair conformation. In 8-methoxy-3-methyl-N-(4-nitrobenzoyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline-1,6-dione, C(18)H(20)N(2)O(6), (II), the heterocyclic ring is in a slightly distorted half-boat conformation, while the other six-membered ring is in a distorted chair conformation. Compound (II) presents a strong intramolecular C-H...O hydrogen bond. In both (I) and (II), the molecules interact through C-H...O interactions.

Self-association and stereochemistry study of 2-methylthio-, 2-dimethylaminocyclohexanone oximes and the parent cyclohexanone oxime.

X-ray diffraction analyses of 2-substituted cyclohexanone oximes C5H9(X)C=NOH [X = SMe (1), NMe2 (2)] and of the parent compound [X = H (3)] showed that their cyclohexyl rings are in a slightly distorted chair conformation. These compounds assume in the solid state the (E) configuration bearing the 2-substituents in the axial conformation. Compounds (1) and (2) exist as dimeric and polymeric hydrogen-bond associates, respectively. Low-temperature X-ray analysis of the cyclohexanone oxime (3) showed that the molecules are associated forming two independent trimers. The dimer in (1) and the trimer in (3) are built up via [O-H...N=C] hydrogen bonds, while the polymer of (2) is via the [OH...NMe2] hydrogen bond. The comparative IR nu(OH) and nu(C=N) analysis of the title compounds, in the solid state and in CCl4 solution, fully supports the nature of the associates for (1)-(3) obtained by X-ray diffraction. The IR azomethyne frequency shift analysis (Deltanu(C=N)) also suggests the occurrence of the pi(C=N)/sigma*(C-X) orbital interaction which stabilizes the axial conformations of (1) and (2).

Fmoc-POAC: [(9-fluorenylmethyloxycarbonyl)-2,2,5,5-tetramethylpyrrolidine-N-oxyl-3-amino-4-carboxylic acid]: a novel protected spin labeled beta-amino acid for peptide and protein chemistry.

The stable free radical 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid (TOAC) is the only spin labeled amino acid that has been used to date to successfully label peptide sequences for structural studies. However, severe difficulty in coupling the subsequent amino acid has been the most serious shortcoming of this paramagnetic marker. This problem stems from the low nucleophilicity of TOAC's amine group towards the acylation reaction during peptide chain elongation. The present report introduces the alternative beta-amino acid 2,2,5,5-tetramethylpyrrolidine-N-oxyl-3-amino-4-carboxylic acid (POAC), potentially useful in peptide and protein chemistry. Investigations aimed at addressing the stereochemistry of this cyclic molecule through X-ray diffraction measurements of crystalline and bulk samples revealed that it consists only of the trans conformer. The 9-fluorenylmethyloxycarbonyl group (Fmoc) was chosen for temporary protection of the POAC amine function, allowing insertion of the probe at any position in a peptide sequence. The vasoactive octapeptide angiotensin II (All, DRVYIHPF) was synthesized by replacing Pro7 with POAC. The reaction of Fmoc-POAC with the peptidyl-resin occurred smoothly, and the coupling of the subsequent amino acid showed a much faster reaction when compared with TOAC. POAC7-AII was obtained in good yield, demonstrating that, in addition to TOAC, POAC is a convenient amino acid for the synthesis of spin labeled peptide analogues. The present findings open the possibility of a wide range of chemical and biological applications for this novel beta-amino acid derivative, including structural investigations involving its differentiated bend-inducing characteristics.

Acetonyldichloro[(Z)-2-chloro-2-phenylvinyl]tellurium(IV), helical chains of metal complexes.

The primary geometry about the Te(IV) atom in the title compound, [TeCl2(C8H6Cl)(C3H5O)] or C11H11Cl3OTe, is a pseudo-trigonal-bipyramidal arrangement, with two Cl atoms in apical positions, and the lone pair of electrons and C atoms in the equatorial plane. The Te(IV) atom is involved in three secondary interactions, two intramolecular [Te...O = 2.842 (3) A and Te.Cl3 = 3.209 (1) A] and one intermolecular [Te...Cl = 3.637 (1) A], the latter giving rise to a helical chain. These helices are linked by C-H...O interchain interactions.

Two polycyclic compounds derived from a Diels-Alder reaction.

In both 9,10-dimethoxy-11-oxatricyclo[6.2.1.0(2,7)]undeca-4,9-diene-3,6-diol, C(12)H(16)O(5), (I), and 5,6-dimethoxy-3,7-dioxatetracyclo[6.4.0.0(2,6).0(4,12)]dodec-9-en-11-ol, C(12)H(16)O(5), (II), the hetero-oxygen-containing five-membered rings have an envelope conformation. The six-membered rings are in a boat conformation in compound (I), and in (II), one is in a half-boat and the other is in a slightly distorted boat conformation. The molecules in both compounds interact through classical hydrogen bonds and C-H.O contacts.

Preferred conformations in the solid state of some alpha-(p-phenylsulfinyl)-p-substituted acetophenones

Information on the geometrical structures of alpha-(p-phenylsulfinyl)-p-substituted acetophenones X-PhC(O)CH2S(O)Ph-Y [X = OMe, Y = H (1); X = NO2, Y = OMe (2); X = OMe, Y = NO2 (3); IUPAC names: (1) 4-methoxyphenyl phenylsulfinylmethyl ketone; (2) 4-nitrophenyl 4-methoxyphenylsulfinylmethyl ketone; (3) 4-methoxyphenyl 4-nitrophenylsulfinylmethyl ketone] have been obtained from X-ray diffraction analyses. A comparison of these results with those previously obtained from X-ray diffraction and ab initio computations of alpha-methylsulfinylacetophenone, PhC(O)CH2S(O)Me, indicated that (1) and (2) adopt in the crystal a cis1 conformation and (3) assumes a quasi-gauche geometry. The stabilization of these conformations in the crystal is discussed in terms of the dipole moment coupling, Coulombic and intramolecular charge transfer interactions between the oppositely charged atoms of the C==O and S==O dipoles. The p-substituted benzene ring is quasi-coplanar with the sulfinyl group for (1) and (3), but is quasi-perpendicular for (2). Conjugation and repulsion between the sulfinyl sulfur lone pair and the pi-benzene ring seem to be responsible for the observed geometries.

7Beta-oxygenated limonoids from Trichilia elegans ssp. elegans.

Five 7beta- and 7alpha-oxygenated obacunone-type limonoids were obtained on reinvestigation of the seeds of Trichilia elegans ssp. elegans: 7-deoxo-7beta-acetoxykihadanins A and B, 7-deoxo-7beta-hydroxykihadanins A and B and 7-deoxo-7alpha-hydroxykihadanin A, the last three being isolated after acetylation procedures as their mono- and/or diacetate derivatives. This is the first report of the natural occurrence of C-7 beta-substituted limonoids without any oxygenated function at C-6. The structures of these compounds have been established on the basis of 1D- and 2D-NMR spectral techniques, ESI-mass spectrum and X-ray crystallographic data.