RESUMEN
A procedure for Ni-catalyzed cross-coupling of ketone enolates with alkenyl halides has been developed. Intermolecular coupling of aromatic and aliphatic ketone lithium enolates with a variety of alkenyl halides is achieved in the presence of Ni(cod)2 catalyst (5 mol %), an N-heterocyclic carbene (NHC) ligand, and LiI (10 mol %) at 6-22 °C for 0.5-12 h with yields of up to 90%. During the initial development of this reaction, a misleading result with respect to the actual active catalyst was obtained using commercially available Q-Phos ligand, which was found to contain a trace of Pd metal contaminant sufficient to catalyze the reaction. However, under the final conditions optimized for Ni(cod)2 in the presence of an NHC ligand, Pd was incompetent as a catalyst.
Asunto(s)
Alquenos/química , Cetonas/química , Níquel/química , CatálisisRESUMEN
A protocol for a mild, catalytic, intermolecular alkenylation of ketone enolates has been developed using a Pd/Q-Phos catalyst. Efficient intermolecular coupling of a variety of ketones with alkenyl bromides was achieved with a slight excess of LiHMDS and temperatures down to 0 °C.
Asunto(s)
Alquenos/química , Alquenos/síntesis química , Hidrocarburos Bromados/química , Cetonas/química , Cetonas/síntesis química , Paladio/química , Catálisis , Técnicas Químicas Combinatorias , Estructura MolecularRESUMEN
A novel electron poor protection group for amines has been developed. It undergoes rapid cleavage by SmI2-Et3N-H2O and its orthogonality towards the regular benzyl carbamate group (CBz) under reductive or transfer hydrogenolytic conditions is reported.
Asunto(s)
Aminas/síntesis química , Carbamatos/química , Etilaminas/química , Yoduros/química , Samario/química , Agua/química , Aminas/química , Estructura MolecularRESUMEN
Sm(HMDS)(2) in n-hexane mediates fast cleavage of primary, secondary and tertiary alkyl fluorides in good to excellent yields. In n-hexane Sm(HMDS)(2) exhibits uniquely enhanced reductive ability towards the C-F bond compared to when using THF as solvent.
Asunto(s)
Alcanos/síntesis química , Hidrocarburos Fluorados/química , Compuestos de Organosilicio/química , Samario/química , Alcanos/química , Estructura Molecular , Oxidación-Reducción , Solventes/químicaRESUMEN
Transition-metal-catalyzed alkenylation of enolates provides a direct method to synthesize broadly useful ß,γ-unsaturated carbonyl compounds from the corresponding carbonyl compound and alkenyl halides. Despite being reported in the early seventies, this reaction class saw little development for many years. In the past decade, however, efforts to develop this reaction further have increased considerably, and many research groups have reported efficient coupling protocols, including enantioselective versions. These reactions most commonly employ palladium catalysts, but there are also some important reports using nickel. There are many examples of this powerful transformation being used in the synthesis of complex natural products.
Asunto(s)
Alquenos/química , Productos Biológicos/síntesis química , Cetonas/química , Níquel/química , Paladio/química , Elementos de Transición/química , Productos Biológicos/química , Ácidos Carboxílicos , Catálisis , Estructura Molecular , EstereoisomerismoRESUMEN
SmI(2)/H(2)O promotes selective α-monodefluorinations, while addition of an amine results in complete α-defluorination reactions.
Asunto(s)
Amidas/química , Etilaminas/química , Halogenación , Yoduros/química , Samario/química , Agua/química , Aminas/química , Ésteres/químicaRESUMEN
A novel combination of SmI(2), KHMDS, and TsCN can be utilized to introduce a cyano group into structurally diverse and highly sensitive 2-alkyl-chroman-4-ones. Subsequent oxidation allows the formed 2-alkyl-3-cyanochromones to be isolated in yields ranging from 49 to 77%. In addition, alpha-bromoketones and esters were found to undergo equally effective alpha-cyanation.
RESUMEN
SmI(2)/amine/water mediates instantaneous cleavage of tosyl amides and tosyl esters. Highly hindered, sensitive and functionalized substrates were successfully deprotected in near quantitative yield.
RESUMEN
The metabolism of monoaromatic hydrocarbons by an iron-reducing bacterial enrichment culture originating from diesel-contaminated groundwater was examined using d7-propylbenzene as a model hydrocarbon. Sequence analysis of the 16S rDNA gene showed that the dominant part (10 of 10 clones) of the enrichment culture consisted of a bacterium closely related to clones found in benzene-contaminated groundwater and to the iron-reducing beta-proteobacterium, Rhodoferax ferrireducens (similarity values were 99.5% and 98.3%, respectively). In degradation studies conducted over 18 weeks, d7-propylphenols were detected by gas chromatography-mass spectrometry (GC/MS) as intra-cellular metabolites concomitant with cell growth in the cultures. The amount of propylphenols increased during the exponential growth phase, and by the end of this phase 4 x 10(-14) moles of ferric iron were reduced and 3 x 10(-15) moles propylphenol produced for every cell formed. During the stationary growth phase the cell density was approximately 10(7) ml(-1), with significantly correlated amounts of propylphenols. Succinate derivates of propylbenzene or phenylpropanol previously shown to be the initial metabolites in the anaerobic degradation of alkylbenzenes could not be identified. This study is the first to report that oxidation of propylbenzene to propylphenols can initiate anaerobic propylbenzene degradation and that iron-reducing bacteria are responsible for this process. In addition, the study shows the importance of taking account of the metabolites adhering to solid phases when determining the extent of biodegradation, so as not to underestimate the extent of the process.