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.

Sedaxane (SDX) 1, isopyrazam (IZM) 2 and Solatenol™ (STL) 3 are broad-spectrum pyrazole carboxamides, which originate from novel chemical classes of fungicides. Their mode of action (MoA) is inhibition of succinate dehydrogenase (SDH), which was recognized for a long time to deliver only compounds with a narrow biological spectrum. This view changed with the market introduction of BASF's boscalid in 2003. All major agro-companies subsequently worked in parallel on this MoA successfully and recently introduced new compounds to the market. Syngenta entered the SDHI area in 1998 and was able to introduce three complementary compounds to the market between 2010 and 2012. In this short review some synthesis challenges and biological effects of SDX 1, IZM 2 and STL 3 will be covered. New cost-efficient synthesis strategies for the preparation of o-biscyclopropyl-aniline, new benzonorbornene intermediates and the key pyrazole carboxylic acid intermediate which is essential for all three Syngenta SDHIs, will be in the focus of this review.

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