1‐Hydroxy‐1H‐benzo[d][1,2,6]oxazaborinin‐4(3H)‐one

The structure of the title compound, C₇H₆BNO₃, a new boron heterocycle, prepared by the condensation of (2‐ethoxycarbonylphenyl)boronic acid and hydroxylamine, reveals the specific mode of intramolecular condensation between a phenylboronic acid and an ortho hydroxamic acid substituent. The crystal structure shows that dehydration occurs to form a planar oxazaborinine ring possessing both phenol‐like B—O—H and lactam functional groups. In the extended structure, intermolecular hydrogen bonding generates a 14‐membered ring. To our knowledge, this is the first crystal structure determination involving a six‐membered ring that exhibits consecutive B—OH, O, NH, and C=O functional groups.     

2∶1 Complex of desoxycholic acid and ethyl acetate: Disorder in the structure at 298 and 163 K

The crystal structure of the 21 channel complex of desoxycholic acid and ethyl acetate has been investigated at 298 and 163 K. The space group isP2₁2₁2₁(No. 19) with four molecules of desoxycholic acid in the unit cell. The ethyl acetate molecules are enclathrated along the 2₁ axes parallel toc and exhibit differing degrees of disorder in the low- and room-temperature structures. Differences in the disorder imply that it is both statistical and dynamic in nature. Our best model for each structure yieldsR=0.064 [R _w =0.058,w=( ₂ F)^–1] andR=0.068 [R _w =0.064,w=( ² F) ^–1 ] for the ambient- and low-temperature studies respectively.IUPAC Nomenclature: 3, 12-dihydroxy-5-cholan-24-oic acid.     

Diastereoselective Synthesis of Novel Benzofuran Derivatives by Euparin as a Natural Compound with DMAD in the Presence of Trialkyl Phosphite

An efficient, simple, and diastereoselective synthesis of novel benzofuran phosphonato ester derivatives has been achieved via a one‐pot three‐component reaction of euparin as a natural product, trialkyl phosphate, and dimethyl acetylenedicarboxylate (DMAD) in diethyl ether without using any catalyst at room temperature. NMR spectroscopic data and X‐ray crystallography analysis are in agreement with the anti arrangement for the two vicinal protons in the structures, and only one diastereoisomer (2S,3R) or (2R,3S) was obtained for the products. The advantage of our research is that this is the first report for the diastereoselective synthesis of phosphonato ester derivatives from a green natural product. This one‐pot reaction occurs in high yields with easy work‐up under mild conditions. All pure products were obtained by recrystallization from ethanol, and there was no need for column chromatography.     

A zwitterion produced by a strong intramolecular N→B interaction in 1‐hydroxy‐2‐(pyridin‐2‐ylcarbonyl)benzo[d][1,2,3]diazaborinine

2‐Acylated 2,3,1‐benzodiazaborines can display unusual structures and reactivities. The crystal structure analysis of the boron heterocycle obtained by condensing 2‐formylphenylboronic acid and picolinohydrazide reveals it to be an N→B‐chelated zwitterionic tetracycle (systematic name: 1‐hydroxy‐11‐oxo‐9,10,17λ⁵‐triaza‐1λ⁴‐boratetracyclo[8.7.0.0^2,7.0^12,17]heptadeca‐3,5,7,12,14,16‐hexaen‐17‐ylium‐1‐uide), C₁₃H₁₀BN₃O₂, produced by the intramolecular addition of the Lewis basic picolinoyl N atom of 1‐hydroxy‐2‐(pyridin‐2‐ylcarbonyl)benzo[d][1,2,3]diazaborinine to the boron heterocycle B atom acting as a Lewis acid. Neither of the other two pyridinylcarbonyl isomers (viz. nicotinoyl and isonicotinoyl) are able to adopt such a structure for geometric reasons. A favored yet reversible chelation equilibrium provides an explanation for the slow D₂O exchange observed for the OH resonance in the ¹H NMR spectrum, as well as for its unusual upfield chemical shift. Deuterium exchange may take place solely in the minor open (unchelated) species present in solution.     

Indachlorins: Nonplanar Indanone‐Annulated Chlorin Analogues with Panchromatic Absorption Spectra between 300 and 900 nm

Indaphyrins, pyrrole‐modified porphyrins containing a cleaved pyrrole β,β′‐bond and two annulated indanone moieties, possess unusually broadened and redshifted UV/Vis spectra because of their π‐expanded chromophores. The parent free base indaphyrin has been crystallographically characterized, highlighting its strongly ruffled conformation incorporating a helimeric twist. It was shown to be susceptible to regiospecific derivatizations at the opposite side of the ring‐cleaved pyrrole (dihydroxylation, followed by functional group transformations of the resulting diol functionality), generating indaphyrin‐based chlorin analogues, indachlorins, that incorporate a dihydroxypyrroline, pyrrolindione, oxazolone, or a morpholine moiety. Structural modifications resulted in further broadening and hyper‐ and bathochromic shifts of the optical spectra, some of which possess a nearly panchromatic absorption between 300 to well above 900 nm. The extents to which these modifications affect their solid‐state conformations were analyzed.     

Hydrogallierungsreaktionen mit den Monoalkinen H5C6‐C≡C‐SiMe3 und H5C6‐C≡C‐CMe3 – cis/trans‐Isomerie und Substituentenaustausch

Hydrogallation Reactions Involving the Monoalkynes H₅C₆‐C≡C‐SiMe₃ and H₅C₆‐C≡C‐CMe₃ – cis/trans Isomerisation and Substituent Exchange Phenyl‐trimethylsilylethyne, H₅C₆‐C≡C‐SiMe₃, reacted with different dialkylgallium hydrides, R₂Ga‐H (R = Me, Et, nPr, iPr, tBu), by the addition of one Ga‐H bond to its C≡C triple bond (hydrogallation). The gallium atoms attacked selectively those carbon atoms, which were also attached to trimethylsilyl groups. The cis arrangement of Ga and H across the resulting C=C double bonds resulted only for the sterically most shielded di(tert‐butyl)gallium derivative, while in all other cases spontaneous cis/trans rearrangement occurred with the quantitative formation of the trans addition products. The diethyl compound Et₂Ga‐C(SiMe₃)=C(H)‐C₆H₅ ( 2 ) gave by substituent exchange the secondary products EtGa[C(SiMe₃)=C(H)‐C₆H₅]₂ ( 7 , Z,Z) and Ga[C(SiMe₃)=C(H)‐C₆H₅]₃ ( 8 ). Interestingly, compound 8 has two alkenyl groups with a Z configuration, while the third C=C double bond has the cis arrangement of Ga and H (E configuration). The reversibility of the cis/trans isomerisation of hydrogallation products was observed for the first time. tert‐Butyl‐phenylethyne gave the simple addition product, R₂Ga(C₆H₅)=C(H)‐CMe₃ ( 9 ), only with di(n‐propyl)gallium hydride.     

Tuning the reduction power of supported gold nanoparticle photocatalysts for selective reductions by manipulating the wavelength of visible light irradiation

Gold nanoparticles supported on CeO(2) were found to be efficient photocatalysts for three selective reductions of organic compounds at ambient temperatures, under irradiation of visible light; their reduction ability can be tuned by manipulating the irradiation wavelength.     

On Eigenvector Bounds

We show under very general assumptions that error bounds for an individual eigenvector of a matrix can be computed if and only if the geometric multiplicity of the corresponding eigenvalue is one. Basically, this is true if not computing exactly like in computer algebra methods. We first show, under general assumptions, that nontrivial error bounds are not possible in case of geometric multiplicity greater than one. This result is also extended to symmetric, Hermitian and, more general, to normal matrices. Then we present an algorithm for the computation of error bounds for the (up to normalization) unique eigenvector in case of geometric multiplicity one. The effectiveness is demonstrated by numerical examples.This revised version was published online in October 2005 with corrections to the Cover Date.