Crystal and Liquid Structures of S-n-Butyl S'-p-tert-Butylbenzyl N-3-Pyridyldithiocarbonimidate (S-1358, Denmert^®) and the S-Alkyl Analogs, Potent Fungicides

Abstract

The structure of S-1358, a potent fungicide toward powdery mildew, has been established by X-ray crystallography as the syn configuration regarding the 3-pyridyl and the S-p-tert-butylbenzyl groups about the N=C bond. On the other hand it instantly gave rise to an equilibrium mixture of the anti and the syn isomers in a number of different solvents (even under deep freezing conditions). The NMR signal due to the benzylic methylene protons could be resolved into two ringlets below -14°C. The isomer (topomer) ratio was dependent linearly on 1/T, and it was also affected by the bulkiness of the S-alkyl group in a series of the analogs. Fungicidal activities of S-1358 and its analogs are discussed in connection with the topomer ratios.