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Approximately 30 % of today's agrochemicals contain at least one sulfur atom. This review article highlights the most important reasons for the fundamental role of sulfur functions in crop protection, such as the occurrence of sulfur in agrochemical pharmacophores, the application of sulfur-containing natural products as lead compounds, the role of sulfur in procidal action, fine-tuning of physico-chemical properties and patent breaking as well as the advantage of sulfur-containing heterocycles compared to their non-sulfur ring isosteres. Case studies from three different mode of action classes give proof, how state-of-the-art organosulfur chemistry enables the synthesis and influences the structure-activity relationships of fungicidally active compounds in the classes of Succinate dehydrogenase inhibitors, tubulin polymerization inhibitors and Cellulose synthase inhibitors.

The rearrangement of a substituted cyclohexyl radical to a cyclopentylmethyl radical on the skeleton of Avermectin B 1 has been investigated using density functional (UB3LYP/6-31G(d)) and G3MP2B3 computational methods. The rearrangement is preferred when highly radical stabilizing groups are present at the 2-and 3-positions of the cyclohexyl radical. A substituent on the 3-position of the cyclohexyl radical enables ring-cleavage of the cyclohexyl radical, while a radical stabilizing substituent on the 2-position of the cyclohexyl radical stabilizes the final cyclopentylmethyl radical, enabling the overall rearrangement and reversing the normal thermodynamic preference for the hexenyl radical ring-closure.