The cover picture (center) shows a CPK model of the structure of a hemicarcerand-a global minimum calculated with the MM2 force field (with the phenylethyl groups omitted). Quite astounding transformations have been carried out in its cavity. Reactions that occur within the host are gold-colored and the one that occurs outside is blue. The golden orb in the middle shows the locations of the guests within the hemicarcerand and highlights the small portal through which the guests enter and exit the interior of the host. "Incarcerated" cyclobutadiene is stable at room temperature and above in the absence of oxygen, but reacts with oxygen that enters the "container" to give incarcerated maleinaldehyde. This new type of chemistry promises to open a whole new field involving the study of electronically and sterically unperturbed reactive species. Review Art icl esOptically active cyanides (l), which are synthetically useful building blocks, may be obtained from naturally occurring a-amino acids (2) in overall yields of up to 60% and with ee values of > 98%. The key feature of the approach discussed here is the isocyanide rearrangement of 3, induced by flash photolysis. Thus this rearrangement, which has long been investigated primarily in terms of mechanism, now constitutes one step in a preparatively useful procedure.

Pre‐emergence herbicides are taken up by seeds before germination and by roots, hypocotyls, cotyledons, coleoptiles or leaves before emergence, whereas post‐emergence herbicides are taken up primarily by foliage and stems. Most modern pre‐emergence herbicides are lipophilic, but post‐emergence herbicides may be lipophilic or hydrophilic. The metabolic conversion of herbicides to inactive or active metabolites after plant uptake is of major importance for some compound classes. Several herbicides are proherbicides as for example some acetyl‐coenzyme A carboxylase (ACCase)‐inhibitors. The physicochemical characteristics of proherbicides and herbicides are usually unrelated. A major role can be attributed to the site of action at a cellular level. A great number of herbicides such as photosystem II (PS II)‐inhibitors, protoporphyrinogen oxidase (PPO)‐inhibitors or carotenoid biosynthesis inhibitors require light for activity. Others, such as cellulose‐biosynthesis and mitotic inhibitors seem to be primarily active in belowground organs. Several lipophilic barriers against the uptake of xenobiotics exist in aboveground and belowground plant parts. The relevance of these barriers needs, however, further clarification. Uptake and translocation models are valuable tools for the explanation of the potential movement of compounds. Many factors other than uptake and translocation have, however, to be considered for the design of herbicides. For post‐emergence herbicides, ultraviolet (UV) light stability, stability in formulations, and mixability with other agrochemicals have to be kept in mind while, in addition to the aforementioned factors soil interaction plays a major role for pre‐emergence herbicides. In our opinion, general physicochemical characteristics of pre‐ or post‐emergence herbicides do, unfortunately not exist yet. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

From several decades, some organophosphorus compounds specifically designed to alter biological systems were introduced on market as agrochemicals (ie glyphosate and glufosinate as herbicides). Nevertheless, it becomes necessary to find new compounds in order to counter plant resistances already observed with glyphosate. Fosmidomicyn and its N-acetyl analogues FR-900098 were perceived as starting points for elaboration of new herbicide candidates, targeting the second enzyme of the non-mevalonate pathway in plants, the 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DOXP reductoisomerase or DXR). It is expected that the enhancement of bioactivity compared to the parent compounds, might be reached by insertion of two fluorine atoms close to the phosphonate function. Indeed, the presence of both fluorine atoms could improve the lipophilicity, affect the pKa of the phosphonic acid function and then induce better activities. Herein, the synthesis of gem-difluorinated analogues of retrohydroxamic fosmidomycin and FR-900098-ester is reported using a radical addition mediated by a cobaloxime complex.

International audienceFosmidomycin (1a) and FR-90098 are potent inhibitors of 1- deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), the second enzyme of the non-mevalonate (MEP) pathway responsible for the biosynthesis of isoprenoids. This paper describes the synthesis of four types of targets bearing a phosphanyl-phosphonic acid motif as the common core for the inhibition of DXR. In these structures, the hydroxamic acid was replaced by various chelators based on a phosphinic acid linked to different functional groups capable of forming fiveor six-membered chelating rings

Bis vor kurzem war die Isocyanid-Cyanid-Umlagerung hauptsachlich als Beispiel fur eine unimolekular verlaufende Gasphasenreaktion bekannt und nur fur einfache Systeme kinetisch untersucht. Kinetikstudien in Losung wurden erst moglich, als man eine iiberlagerte, zum gleichen Produkt fiihrende Radikalkette erkannte und diese inhibieren konnte. Die Geschwindigkeit der Isomerisiernng erwies sich als kaum von der Struktur und von Substituenten abhangig. Allenfalls starke sterische Hinderung in drei Dimensionen wie in tris-a-substituierten Triptycylisocyaniden fiihrt zu einer deutlichen Erhohung der Aktivierungsenthalpie. Die Ergebnisse lassen sich mit einem rein sigmatropen Mechanismus deuten und sind damit in Einklang mit Voraussagen aus ab-initio-Rechnungen. Auch praparativ 1aBt sich diese Umlagerung inzwischen nutzen. Bei der Blitzpyrolyse sind die Ausbeuten an Cyanid nahezu quantitativ. Allylisocyanide reagieren ohne Allylisomerisierung und optisch aktive Isocyanide unter vollstandiger Retention. Die Umlagerung kann sowohl Bestandteil wirtschaftlich interessanter Synthesen, z. B. der Entziindungshemmer Ibuprofen und (9-Naproxen, sein als auch beim Aufbau optisch aktiver P-Acyloxycyanide, die niitzliche Synthesebausteine sind, aus optisch aktiven cl-Aminosauren helfen.