Paul Kiprof

Synthesis and structure of benzoboroxoles: novel organoboron heterocycles

Abstract Benzoboroxoles (5) can be prepared from the readily available o-bromobenzyl alcohols via dilithiation followed by reaction with triisopropylborate. X-Ray structural analysis of 1-hydroxy-3(1H)-1,2-benzoboroxole (5a) as well as the results of ab initio molecular orbital calculations indicate a planar structure of the boron center with a relatively short Cue5f8B bond. Preliminary results regarding the chemistry of benzoboroxoles are also reported.

Synthesis and reactions of amino acid-derived benziodazole oxides: new chiral oxidizing reagents

The novel benziodazole oxides (3) can be prepared by oxidation of the readily available 2-iodobenzamides (5 or 6) with potassium bromate. Benziodazole oxides can find practical application as selective oxidizing reagents analogous to the widely used Dess–Martin periodinane (1) and benziodoxole oxide (2). Preliminary results indicate that reagents 3 can oxidize primary alcohols to aldehydes, while non-symmetric sulfides are oxidized to chiral sulfoxides with moderate enantioselectivity.

Systematic color tuning of a family of luminescent azole-based organoboron compounds suitable for OLED applications

A new tunable luminescent family of heterocyclic aromatic compounds containing boron has been prepared and characterized through NMR spectroscopy, mass spectrometry, absorption and fluorescence spectroscopy as well as structural study using single crystal X-ray crystallography. Spectroscopic properties of the new compounds were also studied using DFT and TDDFT computational models that showed very good agreement of the theoretical data with experimental results. Through introduction of auxochromic atoms such as sulfur and extension of the π system of the ligands it is possible to cover a large range of the visible spectrum. Activation and enhancement of the luminescence is achieved by condensation reactions that introduce the boron fragment forming stable, sublimable compounds suitable for OLED applications.

Selective synthesis of four- and five-membered metallaheterocycles via CC bond-forming reactions of η2-iminoacyl and η3-1-azaallyl complexes of tungsten with alkyl isocyanides

Abstract Efficient procedures for the synthesis of four- and five-membered tungstenaheterocycles are reported, starting from the readily accessible η 2 -iminoacyl and η 3 -1-azaallyl complexes Cp*(CO) 2 W[η 2 -C(NEt)Me] ( 1 ) and ( 2 ) (Cp* = η 5 -C 5 Me 5 ), respectively. A clean isocyanide insertion into the metalue5f8iminoacyl-carbon bond occurs when 1 is heated with RNC (R = Me, Et), leading to the η 2 -1,4-diaza-3-methylbutadien-2-yl complexes Cp*(CO) 2 W[C(NR)C(N Et)Me] ( 3 : R = Me; 4 : R = Et). Similarly complex 2 reacts with RNC (R = Me, Et), by insertion of the isocyanide into the metalue5f8azaallyl-carbon bond, to afford the metallacyclic aminocarbene complexes Cp*(CO) 2 W[C(NHR)C(H)C(H)N Et] ( 5 : R = Me; 6 : R = Et). Atautomeric equilibrium between the aminocarbene complexes and their imino counterparts Cp*(CO) 2 W[C(NR)CH 2 C(H)N Et] (R = Me, Et) is suggested by the H/D exchange of the amino and one vinyl hydrogen observed in the acid-catalyzed reaction of 5 with D 2 O to yield Cp*(CO) 2 W[C(NDR)C(D)C(H)N Et] 5 ′). Determination of the solid-state structure of 6 by a single-crystal X-ray diffraction study has revealed a “four-legged piano stool” complex with a planar five-membered metallaheterocycle. The intraannular bond lengths indicate π-electron delocalization within the cycle. A close analogy between 5 and 6 and 3-aminopyrroles is discussed in terms of reactivity and spectroscopic and structural data.

New Bioactive Bromotyrosine-Derived Alkaloid from a Marine Sponge Aplysinella sp

A new bromotyrosine-derived alkaloid, (+)-aplysinillin (1), together with seven known compounds, was isolated from the crude organic extract of the marine sponge Aplysinella sp. collected from the Federated States of Micronesia. The structure of 1 was deduced by NMR and mass spectral techniques. Compounds 1-8 were evaluated for their inhibitory activity with the hyphae formation inhibition assay in Streptomyces 85E. Compounds 1 and 8 exhibited antiproliferative activities against the human breast adenocarcinoma cancer cell line MCF-7.

The effect of solubility on the stability of titanium(IV) arene complexes derived from hexasubstituted arenes and TiCl4

Abstract The investigation of new titanium(IV) hexaalkylarene complexes gave new insight into the stability of high-valent metal arene complexes. In contrast to low-valent transition metal arene complexes these complexes are in equilibrium with the free arenes. The stability of the complexes was shown to depend strongly on both the donor ability of the arene and on their solubility. This is unprecedented in transition metal arene chemistry.

3H-2,1-Benzoxaborole-1-spiro-4′-(5-oxa-3a-aza-4-borapyrene)

In the title compound, C20H14BNO2, the B atom has a tetrahedral geometry with two short B—O and two long B—C and B—N bonds, revealing a significant difference between Car—O—B and Calkyl—O—B bond distances. Intermolecular Ar—H⋯O hydrogen bonds and strong π–π interactions (3.368u2005Å) between aromatic cores of neighbouring molecules result in hexagonal channels along the crystallographic c axis, which are potentially accessible for small molecules.

An ab initio study of annulation effects on the valence isomerism of benzene

Abstract Annulation should tilt the benzene/Dewar-benzene equilibrium toward benzene, the largest effective annulating ring being six-membered; MP2(fc)/6-31G*//RHF/6-31G* methods are needed to reproduce experimental isomerization energies, but 6-31G calculations suffice to show trends for molecular design. Download : Download full-size image Smaller “n” should favor isomerization; effective rings will have n≤6.