Over the past decade, the most significant, conceptual advances in the field of fluorination were enabled most prominently by organo- and transition-metal catalysis. The most challenging transformation remains the formation of the parent C-F bond, primarily as a consequence of the high hydration energy of fluoride, strong metal-fluorine bonds, and highly polarized bonds to fluorine. Most fluorination reactions still lack generality, predictability, and cost-efficiency. Despite all current limitations, modern fluorination methods have made fluorinated molecules more readily available than ever before and have begun to have an impact on research areas that do not require large amounts of material, such as drug discovery and positron emission tomography. This Review gives a brief summary of conventional fluorination reactions, including those reactions that introduce fluorinated functional groups, and focuses on modern developments in the field.

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Introduction of Fluorine and Fluorine-Containing Functional Groups

Metal-catalyzed carbon-sulfur bond formation.

In recent years, the use of essential oils (EOs) derived from aromatic plants as low-risk insecticides has increased considerably owing to their popularity with organic growers and environmentally conscious consumers. EOs are easily produced by steam distillation of plant material and contain many volatile, low-molecular-weight terpenes and phenolics. The major plant families from which EOs are extracted include Myrtaceae, Lauraceae, Lamiaceae, and Asteraceae. EOs have repellent, insecticidal, and growth-reducing effects on a variety of insects. They have been used effectively to control preharvest and postharvest phytophagous insects and as insect repellents for biting flies and for home and garden insects. The compounds exert their activities on insects through neurotoxic effects involving several mechanisms, notably through GABA, octopamine synapses, and the inhibition of acetylcholinesterase. With a few exceptions, their mammalian toxicity is low and environmental persistence is short. Registration has been the main bottleneck in putting new products on the market, but more EOs have been approved for use in the United States than elsewhere owing to reduced-risk processes for these materials.

Essential oils in insect control: low-risk products in a high-stakes world.

https://chemistry.mdma.ch/hiveboard/rhodium/pdf/piper.phytochemistry.pdf

Phytochemistry of the genus Piper

The long term use of many insecticides is continually threatened by the ability of insects to evolve resistance mechanisms that render the chemicals ineffective. Such resistance poses a serious threat to insect pest control both in the UK and worldwide. Resistance may result from either an increase in the ability of the insect to detoxify the insecticide or by changes in the target protein with which the insecticide interacts. DDT, the pyrethrins and the synthetic pyrethroids (the latter currently accounting for around 17% of the world insecticide market), act on the voltage-gated sodium channel proteins found in insect nerve cell membranes. The correct functioning of these channels is essential for normal transmission of nerve impulses and this process is disrupted by binding of the insecticides, leading to paralysis and eventual death. Some insect pest populations have evolved modifications of the sodium channel protein which prevent the binding of the insecticide and result in the insect developing resistance. Here we review some of the work (done at Rothamsted Research and elsewhere) that has led to the identification of specific residues on the sodium channel that may constitute the DDT and pyrethroid binding sites.

https://iubmb.onlinelibrary.wiley.com/doi/epdf/10.1080/15216540701352042

DDT, pyrethrins, pyrethroids and insect sodium channels.

Since S-n-butyl S′-p-tert-butylbenzyl N-3-pyridyldithiocarbonimidate, a potent fungicide to powdery mildew, is known to inhibit ergosterol biosynthesis in Monilinia fructigena, the activities were assessed on 24 compounds having other substituents than the 3-pyridyl and on 24 compounds having a variety of different structures connecting the 3-pyridyl and the p-tert-butylphenyl group from that of the dithiocarbonimidate.In the former group the 3-pyridyl group was essential for the activities and the substitution at the 2- or 6-position resulted, on available data, in inactive compounds. Several other β-N-heterocyclic analogs were also active. In the latter group, a number of modified compounds from the dithiocarbonimidate structure were shown to be active.

Structure Modifications of S-n-Butyl S'-p-tert-Butylbenzyl N-3-Pyridyldithiocarbonimidate (S-1358, Denmert®) and Fungicidal Activities

Specific deamination of 4-amino-1,2,4-triazin-5(4H)-ones by catalytic oxidation with t-butylhydroperoxide. A chemical model for metabolism of 1,2,4-triazine herbicides

Since S-n-butyl S'-p-tert-butylbenzyl N-3-pyridyldithiocarbonimidate, a potent fungicide to powdery mildew, is known to inhibit ergosterol biosynthesis in Monilinia fructigena, the activities were assessed on 24 compounds having other substituents than the 3-pyridyl and on 24 compounds having a variety of different structures connecting the 3-pyridyl and the p-tert-butylphenyl group from that of the dithiocarbonimidate. In the former group the 3-pyridyl group was essential for the activities and the substitution at the 2- or 6-position resulted, on available data, in inactive compounds. Several other β-N-heterocyclic analogs were also active. In the latter group, a number of modified compounds from the dithiocarbonimidate structure were shown to be active.

/pdf/structure-activity-study-of-s-1358-and-its-derivatives-ii-buv9j1bews.pdf

Structure-activity study of S-1358 and its derivatives. II. Structure modifications of S-n-butyl S'-p-tert-butylbenzyl N-3-pyridyldithiocarbonimidate (S-1358, Denmert) and fungicidal activities.

Regiospecific preparation and allylation of fluoromethyl ketone enol ethers via fluoro-olefination of 1,2,3-triol derivatives

Initially, a number of important or established synthetic pyrethroids containing the chrysanthemate moiety are introduced, and there are also described the relative insecticidal potencies of specific stereoisomers of the chrysanthemates resulting from acid stereochemistry. Recently, many studies on structure modification of the acid moiety of pyrethroid have disclosed a number of the most distinguished synthetic pyrethroids containing diversely modified acid moieties, which have been successfully developed as the most outstanding pyrethroid insecticides in the recent years.Since a majority of the chrysanthemates now have been reinforced on the insecticidal potency basis by the synthetic selection of useful stereoisomers, various relevant methods of synthesis are progressively reviewed on optical resolutions followed by racemizations, a stereoselective synthesis and/ or a synthesis by asymmetric induction of optically active chrysanthemic acids in close reference to the insecticidal activities of resultant stereoisomers. Relevant methods leading to all the fenvalerate stereoisomers and specific stereoisomer mixtures resulting from the chirality of the alcohol moiety are also described.Finally, some of specific advantages that are delivered by the stereoisomer selection are commented regarding the insecticidal performance aspects essentially linked with developmental potentials of the synthetic pyrethroids.

/pdf/chemistry-and-actions-of-the-recent-synthetic-pyrethroids-4n2gn30z8a.pdf

Hirosuke Yoshioka

Papers

Structure Modifications of S-n-Butyl S'-p-tert-Butylbenzyl N-3-Pyridyldithiocarbonimidate (S-1358, Denmert®) and Fungicidal Activities

Specific deamination of 4-amino-1,2,4-triazin-5(4H)-ones by catalytic oxidation with t-butylhydroperoxide. A chemical model for metabolism of 1,2,4-triazine herbicides

Structure-activity study of S-1358 and its derivatives. II. Structure modifications of S-n-butyl S'-p-tert-butylbenzyl N-3-pyridyldithiocarbonimidate (S-1358, Denmert) and fungicidal activities.

Regiospecific preparation and allylation of fluoromethyl ketone enol ethers via fluoro-olefination of 1,2,3-triol derivatives

Chemistry and Actions of the Recent Synthetic Pyrethroids and their Stereoisomers.