Mohammad R. Karim

Transannular aldol condensations within macrocyclic lactones: A novel approach to 8-membered carbocyclic rings.

Abstract A novel method has been developed for the construction of 8-membered carbocyclic rings, involving as the key step a chemoselective transannular aldol condensation within an 11-membered ketolactone ring.

Pulping catalysts from lignin (5). Nitrogen dioxide oxidation of lignin models to benzoquinones

ABSTRACT Several syringyl lignin models have been oxidized to 2,6-dimethoxy- p-benzoquinone (DMBQ) in high yields with nitrogen dioxide (NO2) in methanol solvent. The yields of DMBQ were high for syringyl alcohol, syringaldehyde, and disyringyl methane and moderate for several other phenolic syringyl models. Benzoquinones were not formed from non phenolic substrates. The yields were slightly improved by the presence of N- hydroxysuccinimide. Guaiacyl lignin model compounds gave low benzo-quinone yields; the major products were C-5 nitro substituted compounds. A radical mechanism is proposed to explain the observed results.

Octyl (2E)-2-[2-(di-phenyl-phosphan-yl)benzyl-idene]hydrazinecarbodi-thio-ate.

The title compound, C28H33N2S2P, adopts the thione tautomeric form, as supported by the C—S distance [1.6744 (18) Å]. The Schiff base exhibits an E conformation about the C=N bond but a Z conformation about the C—N bond. The terminal chain is disordered over two sets of sites with an occupancy ratio of 0.732 (3):0.268 (3). In the crystal, pairs of N—N—H hydrogen bonds between the thione groups link neighbouring molecules into centrosymmetric dimers.

2,9-Bis(1,3-benzothia­zol-2-yl)-1,10-phenanthroline dichloro­methane disolvate

In the title compound, C26H14N4S2·2CH2Cl2, the two pendant benzothiazole groups are slightly twisted with respect to the phenanthroline core [dihedral angles = 1.03 (7) and 9.05 (5)°]. Weak intermolecular C—H⋯N and C—H⋯Cl interactions occur in the crystal structure.

2,9-Bis(5-sulfanylidene-4,5-di-hydro-1,3,4-oxa-diazol-2-yl)-1,10-phenanthroline dimethyl sulfoxide disolvate.

In the title compound, C16H8N6O2S2·2C2H6OS, the phenanthroline molecule resides on a twofold axis, and the asymmetric unit also contains a slightly disordered [occupancy ratio for S atom of 0.95 (3):0.047 (3)] molecule of dimethyl sulfoxide. The O atoms of the solvent molecule accept hydrogen bonds from the N—H groups of the five-membered 2,3-dihydro-1,3,4-oxadiazole-2-thione ring. This ring is nearly coplanar with the phenanthroline ring, with a dihedral angle between their least-squares planes of 8.86 (6)°. In the crystal, the molecules are linked by C—H⋯O interactions.