Synthesis and crystal structures of two purpurin derivatives: 1,4-dihydroxy-2-propoxyanthraquinone and 2-butoxy-1,4-dihydroxyanthraquinone

The title compounds were obtained by deprotonation of 1,2,4-trihydroxyanthraquinone (purpurin) using sodium hydride followed by reaction with either 1-bromopropane or 1-bromobutane. 1,4-Dihydroxy-2-propoxyanthraquinone crystallizes as a 1:1 solvate from acetonitrile, C17H14O5·CH3CN. The anthraquinone core of the molecule is essentially planar and both hydroxy groups participate in intramolecular O—H...O (carbonyl) hydrogen bonds. The propyl chain is angled slightly above the plane of the anthraquinone moiety with a maximum deviation of 0.247 (2) Å above the plane for the terminal carbon atom. In contrast, 2-butoxy-1,4-dihydroxyanthraquinone, C18H16O5, crystallizes from nitromethane with two independent molecules in the asymmetric unit. The anthraquinone core of each independent molecule is essentially planar and both hydroxy groups on both molecules participate in intramolecular O—H...O(carbonyl) hydrogen bonds. The butyl chain in one molecule is also angled slightly above the plane of the anthraquinone moiety, with a maximum deviation of 0.833 (5) Å above the plane for the terminal carbon atom. In contrast, the butyl group on the second molecule is twisted out of the plane of the anthraquinone core with a torsion angle of 65.1 (3)°, resulting in a maximum deviation of 1.631 (5) Å above the plane for the terminal carbon atom.

Synthesis of 8-homocastanospermine

The 1,3-dipolar cycloaddition of a five-membered cyclic nitrone derived from malic acid (4) and unsaturated D-threo-hexaldonolactone (1) leads to a single adduct 6, which can be transformed into the 8-homocastanospermine (13) via a sequence involving rearrangement of the six-membered lactone ring into the five-membered one, removal of the terminal carbon atom from the sugar chain, cleavage of the N—O bond, and the intramolecular alkylation of the nitrogen atom. The iminosugar (13) does not show any interesting inhibitory activity towards α- and β-glucosidases.Key words: iminosugars, homocastanospermine, nitrones, aldono-1,5-lactone, 1,3-dipolar cycloaddition, glucosidases.

Notizen: Tricarbonyliron Complexes - Observation of 13C(CO) NMR Signals via Polarization Transfer

Improvements in the detection of 13C(CO) resonances by using polarization transfer techniques, based on long-range coupling constants nJ(13C(CO)1H) = 1 ±0.1 Hz (n > 3), are reported. Coupling constants between 13C(CO) and other rare spin-1/2 nuclei have been observed, and longrange 13C(CO)-1H coupling have been traced by two-dimensional (2D ) 13C/1H heteronuclear shift correlations (HETCOR). Seven tricarbonyliron complexes 1 to 5 serve as examples in which the [Fe(CO)3] fragment is linked to cyclic dienes (siloles: 1a, b; 1,1′-spirobisilole: 2), and to cyclic heterodienes derived from substituted 2,5-dihydro- 2,5-silaboroles [1-aza (3a, b); 1-thia (4); 1-selena (5)]. In the case of complex 5, it was possible to resolve the 77Se satellites with 2J( 77Se13C(CO )) = 4.4 Hz. In 2D 13C (CO )/1H HETCOR experiments it was shown that polarization transfer originates mainly from C-methyl groups [4J( 13C(CO)/1H (M ))], adjacent to the “terminal” carbon atom(s) of the cyclic diene or heterodiene system which are linked to the [Fe(CO)3] fragment.

MINDO-Forces Study of Phenyl and Cyclopropyl Substituted Allyl Cations and Anions

MINDO-force calculations have been performed on phenyl and cyclopropyl substituted allyl cations and anions with complete energy minimization. It is found that the phenyl ring destabilizes the allyl cations when substituted at the terminal and at the center carbon atom of the cation, while the cyclopropyl ring stabilizes the allyl cation when substituted at the terminal carbon atoms, but destabilizes the cation when substituted at the center carbon atom of the cation. These results agree with the experimental ones. In the case of the allyl anions, it is found that the phenyl ring destabilizes the allyl anions when substituted on the terminal and on the center carbon atoms of the allyl anions, while the cyclopropyl ring stabilizes the allyl anion when substituted on the terminal carbon atom but destabilizes the anion when substituted on the center carbon atom. Also, it is found that both the phenyl and cyclopropyl rings are electron withdrawing when substituted on the allyl anions, while they are electron donating when substituted on the allyl cations.

Intramolecular Diels-Alder Additions of Benzynes to Furans. Exploratory Studies

A series of 3-alkoxyanthranilic acids, in which a furan ring is attached to the terminal carbon atom of the alkoxy group, has been prepared. When the chain linking the anthranilic acid and furan ring systems is three or four atoms long, decomposition of the derived diazonium chlorides generates the corresponding benzynes , which are efficiently trapped intramolecularly by the furan moiety. Diazotization of 2-amino-3-furfuryloxybenzoic acid, where the linking chain is two atoms long, results in fragmentation with the formation of 6-diazo-5- oxocyclohexa-1,3-diene-1-carboxylic acid.

13C—NMR-Spektren und Bindungsverhältnisse von Ketenen / 13C—NMR-Spectra and Bonding Situation of Ketenes

18C-NMR spectra of alkyl- and arylsubstituted ketenes are reported1e. The terminal carbon atom resonances are found at extreme highfield positions ranging from 2.5 ppm to about 50 ppm. They are the most shielded sp2-carbon-atoms observed until now. The central carbon atom resonances appear from about 190 ppm to 206 ppm. From comparisons of the chemical shifts of the ketene carbon atoms with that of analogously substituted alienes and olefines conclusions concerning the bonding situation in ketenes are drawn.

Hydroboration of acyclic allenes with disiamylborane

The present investigation demonstrates the hydroboration of 1,2-nonadiene, phenylpropadiene, 3-phenyl-1,2-butadiene, 4,5-nonadiene, and tetramethylallene with disiamylborane. All the allenes except tetramethylallene underwent 100% conversion. Examination of the products indicated preferential electrophilic attack of boron on the least substituted terminal carbon atom in the case of 1,2-nonadiene, phenylpropadiene, 3-phenyl-1,2-butadiene, and on the central carbon atom in 4,5-nonadiene. In tetramethylallene boron, attack was exclusively on the central carbon atom. These results have been explained in terms of steric effects on a four-centered transition state.