RESUMO
The present study of the chemistry of short-lived α-fluorocarbocations reveals that even inactive methyl carbons can serve as nucleophiles, attacking a cationic center. This, in turn, facilitates the synthesis of a cyclopropane ring in certain triterpene backbones. We report the synthesis of compounds similar to 2, containing a bridgehead cyclopropane, and compounds of type 3 with an 11 membered bicyclic ring consisting of two bridgehead double bonds (anti-Bredt) within a triterpene skeleton. The synthesis involves three unconventional chemical processes: (a) a methyl group serving as a nucleophile; (b) the unexpected and unprecedented synthesis of a strained system in the absence of an external neighboring trigger; and (c) the formation of an 11-membered bicyclic diene ring within a triterpenoid skeleton. An α-fluorocarbocation mechanism is proposed and supported by density functional theory calculations.
RESUMO
Flavonoids are abundant micronutrients in our diet, possessing various biological activities. Fluorine was successfully added across the double bond of various flavones and chromones. The difluoro derivative products were easily dehydrofluorinated to form the corresponding 3-fluoroflavones and 3-fluorochromones.
Assuntos
Produtos Biológicos/química , Cromonas/química , Flavonas/química , Flavonoides/química , Flúor/química , Espectroscopia de Ressonância Magnética , Estrutura MolecularRESUMO
Clonal propagation of plants by induction of adventitious roots (ARs) from stem cuttings is a requisite step in breeding programs. A major barrier exists for propagating valuable plants that naturally have low capacity to form ARs. Due to the central role of auxin in organogenesis, indole-3-butyric acid is often used as part of commercial rooting mixtures, yet many recalcitrant plants do not form ARs in response to this treatment. Here we describe the synthesis and screening of a focused library of synthetic auxin conjugates in Eucalyptus grandis cuttings and identify 4-chlorophenoxyacetic acid-L-tryptophan-OMe as a competent enhancer of adventitious rooting in a number of recalcitrant woody plants, including apple and argan. Comprehensive metabolic and functional analyses reveal that this activity is engendered by prolonged auxin signaling due to initial fast uptake and slow release and clearance of the free auxin 4-chlorophenoxyacetic acid. This work highlights the utility of a slow-release strategy for bioactive compounds for more effective plant growth regulation.
RESUMO
Aryl boronic acids or pinacol esters containing EDG were converted in good yields and fast reactions to the corresponding aryl fluorides using the readily obtainable solutions of AcOF. In reactions with aryl boronic acids containing EWG at the para position, there are two competing forces: one directing the fluorination to take place ortho to the boronic acid and the other, toward an ipso substitution. With EWG meta to the boronic acid, substitution ipso to the boron moiety takes place in good yields.
Assuntos
Acetatos/química , Ácidos Borônicos/química , Flúor/química , Hidrocarbonetos Fluorados/síntese química , Ésteres/química , Hidrocarbonetos Fluorados/química , Estrutura MolecularRESUMO
Activation of the relatively inactive polypyridine backbone with strong electrophilic fluorine, originating from acetyl hypofluorite (AcOF) enables attack of the acetoxy moiety at the α position to the heteroatom. Derivatives of bipyridine, phenanthroline and terpyridine systems have been acetoxylated or oxygenated within a few minutes usually in very good yields.
RESUMO
A mild and very efficient method for converting boronic acids to alcohols has been developed using the acetonitrile complex of hypofluorous acid HOF·CH3CN. Employing (18)O-labeled water results in alcohols containing a heavy oxygen isotope. The reactions were performed at room temperature, within a few minutes and in excellent yields.