Jost H. Bieri

The constitution of vertinolide, a new derivative of tetronic acid, produced by Verticillium intertextum☆

Abstract From the culture of Verticillium intertextrum a new tetronic acid derivative, vertinolide, has been isolated as the main constituent of the chloroform extract. Structure 1a was established for vertinolide by X-ray diffraction analysis. Vertinolide (1a) was also transformed to an O-methyl-(1b), an O-acetyl-(1c), a tetrahydro- (1d) and a tetrahydro-O-methyl-derivative (4). The spectroscopic properties of 1a, of its derivatives 1a, 1c, 1d and 4 as well as of three model compounds are compared and discussed.

On the structure of [η4-2,5-bis(trimethylsilyl)cyclopentadienone](η5-cyclopentadienyl)cobalt

X-ray diffraction study has been carried out on [η 4 -bis(trimethylsilyl)cyclopentadienone](η 5 -cyclopentadienyl)cobalt (I), the first example of a (η 4 -cyclopentadienone)(η 5 -cyclopentadienyl)cobalt complex with only two substituents on the cyclopentadienone ring. Complex I crystallizes in space group P 2 1 / c with four molecules in the unit cell and lattice parameters a 6.5259(5), b 12.2378(9), c 21.8397(15) A and β 90.442(7)°. Extended Huckel MO calculations are discussed for a simpler model, namely the parent cyclopentadienone complex (III).

Kinetics and mechanisms of nucleophilic displacements with heterocycles as leaving groups. Part 25. X-Ray structure determinations, crystallographic evidence for steric crowding, and correlation with acceleration of rates

X-Ray crystallographic structures are determined for seven N-benzylpyridinium salts including compounds possessing free, five-ring fused, and six-ring fused α-phenyl groups. Significant bond lengths, non-bonding distances, torsional and interplanar angles are determined and compared for the eight structures (the triphenyl derivative was found in two crystal environments). The results show steric overcrowding to an extent that parallels the kinetic displacement rates. However, the steric strain existing in all these molecules is relieved to different extents by different distortions in the different molecules. Nevertheless, crystallographic interatomic distances and angles are shown to be of potential utility in determining the type of mechanistic changes to be undergone, provided the appropriate parameters are selected.

A novel photochemical rearrangement of allenic esters

The alkyl allenic esters (1a–c) on irradiation are found to afford the cyclobutenones (2a–c) while the phenyl ester (1e) affords the photo-Fries product (4).