Retrosynthetic strategies for the preparation of heterocyclic rings present in pesticides

The retrosynthetic approach for the preparation of heterocycles is a highly useful synthetic strategy based on a disconnection analysis consisting in the construction of the target molecule by going steps backwards through the precursors and conditions needed. This study intends to give classical and more updated examples of methods for preparing five and six members rings which are more diverse and widespread in pesticides used to control, unwanted or harmful insects, rodents, or weeds. The schemes used in this study tend to avoid multi schematic pathways focussing on the key steps and synthons required, obviating the dehydrations, molecular hydrogen loss or beta eliminations which are the main events during the aromatization processes. The arrows represent the interactions between the reactive sites existing within the functionalities of each intermediate in a way to show from a perspective view in which way the annulation process is taking place, and the new bonds formed during the heterocyclic ring formation are highlighted in colour for better understanding. The approaches outlined are classified in five and six member rings fused and not fused, and with one or two heteroatoms, giving examples of pesticides either synthetic or natural with an heterocyclic moiety and their impact and applicability in agriculture.