Tautomerism and stereochemistry of dihydroxyperylenequinones: Force field investigations

摘要

Stereochemistry and tautomerism of cercosporin and several of its partial structure models were investigated using an MM2 derived force field method. Besides the “propeller” type conformer, which was found before by X-ray crystallography, the complicated energy hypersurface was shown to contain a novel “double-butterfly” conformer of similar stability. The interconversion barrier between these conformers and their enantiomers was found to be unusually high due to buttressing effects of neighbor substituents. Judged from the calculations, the 4,9-tautomer of cercosporin could also be present in favoring instances besides the 3,10-tautomer, whereas the 3,9-tautomer is strongly desta