(Z)-2-(2-Hy-droxy-4-meth-oxy-benzyl-idene)-1-benzofuran-3(2H)-one.

In the title compound, C(16)H(12)O(4), the 1-benzofuran-one unit is in a planar conformation [C-C-C-C = 179.69 (12)°]. The conformation around the C=C double bond [1.3370 (17) Å] is Z. In the crystal, the mol-ecules are stabilized by O-H⋯O (running parallel to the bc plane) and C-H⋯O hydrogen bonds.

Nimbolide and isonimbolide.

Nimbolide 1, a potent molecule of biological significance, was isolated. Attempts were made to cleave the ether linkage in nimbolide using boron trifluoride etherate in the presence of tetrabutyl ammonium bromide so as to generate a ring-opened structure akin to azadirachtins, which are known to possess excellent antifeedant properties. However, a novel rearranged product was envisaged during the course of the reaction, which was determined as isonimbolide 2-a structural isomer of nimbolide through spectroscopic methods.

The isomeric compounds nimbolide and isonimbolide.

Nimbolide [systematic name: (4alpha,5alpha,6alpha,7alpha,15beta,17alpha)-7,15:21,23-diepoxy-6-hydroxy-4,8-dimethyl-1-oxo-18,24-dinor-11,12-secochola-2,13,20,22-tetraene-4,11-dicarboxylic acid gamma-lactone methyl ester], C27H30O7, was isolated from the leaves of Azadirachta indica, and its isomer, isonimbolide [systematic name: (4alpha,5alpha,6alpha,7alpha,15alpha)-7,15:21,23-diepoxy-6-hydroxy-4,8-dimethyl-1-oxo-18,24-dinor-11,12-secochola-2,16,20,22-tetraene-4,11-dicarboxylic acid gamma-lactone methyl ester], was prepared from a novel rearrangement reaction of nimbolide, using boron trifluoride etherate and tetrabutylammonium bromide. The reaction conditions are probably responsible for the ether cleavage, double-bond rearrangement and reformation of the ether linkage. As a result, there are conformational changes in two cyclopentane rings and the side-chain -CH2COOMe group. In isonimbolide, an R(4)(4)(24) hydrogen-bond motif is observed.

8-(2-bromo-3-methoxy-3-methylbutyl)-7-methoxycoumarin.

The title compound, C(16)H(19)BrO(4), is a derivative of osthol, isolated from the seeds of Imperatoria Osthruthium. The structure was solved in space group P-1, with two molecules in the asymmetric unit, and was refined to a final R factor of 0.064. The two molecules in the asymmetric unit differ in the orientation of their brominated substituent group. The benzopyran ring displays aromatic character. The packing of the molecules in the lattice is mainly due to C-H...O hydrogen bonds.