RESUMEN
Using an iridium catalyst modified by PhanePhos, CF3-allenes react with methanol to form branched products of hydrohydroxymethylation as single regioisomers with excellent levels of enantiomeric enrichment. This hydrogen autotransfer process enables catalytic enantioselective formation of acyclic CF3-bearing all-carbon quaternary stereocenters in the absence of stoichiometric metals or byproducts.
Asunto(s)
Alquenos/química , Carbono/química , Fluorocarburos/química , Iridio/química , Metanol/química , Catálisis , Metilación , Estructura Molecular , EstereoisomerismoRESUMEN
Osmium(0) complexes derived from Os3(CO)12 and XPhos (2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl) catalyze the C-C coupling of α-hydroxy esters 1a-1i, α-ketols 1j-1o, or 1,2-diols dihydro-1j-1o with ethylene 2a to form ethylated tertiary alcohols 3a-3o. As illustrated in couplings of 1-octene 2b with vicinally dioxygenated reactants 1a, 1b, 1i, 1j, 1k, 1m, higher α-olefins are converted to adducts 4a, 4b, 4i, 4j, 4k, 4m with complete levels of branched regioselectivity. Oxidation level independent C-C coupling is demonstrated by the reaction of 1-octene 2b with diol dihydro-1k, α-ketol 1k, and dione dehydro-1k. Functionalized olefins 2c-2f react with ethyl mandelate 1a to furnish adducts 5a-8a as single regioisomers. The collective data, including deuterium labeling studies, are consistent with a catalytic mechanism involving olefin-dione oxidative coupling to form an oxa-osmacyclopentane, which upon reductive cleavage via hydrogen transfer from the secondary alcohol reactant releases the product of carbinol C-alkylation with regeneration of the ketone. Single-crystal X-ray diffraction data of the dinuclear complex Os2(CO)4(O2CR)2(XPhos)2 and the trinuclear complex Os3(CO)11(XPhos) are reported. These studies suggest increased π-backbonding at the stage of the metal-olefin π-complex plays a critical role in facilitating alkene-carbonyl oxidative coupling, as isostructural ruthenium(0) complexes, which are weaker π-donors, do not catalyze the transformations reported herein.
Asunto(s)
Alquenos/química , Etilenos/química , Osmio/química , Catálisis , Cristalografía por Rayos X , Ésteres/química , Hidrogenación , Análisis Espectral/métodosRESUMEN
A strategy for catalytic vinyl transfer from enol carboxylates to activated secondary alcohol C-H bonds is described. Using XPhos-modified ruthenium(0) or osmium(0) complexes, enol carboxylate-carbonyl oxidative coupling forms transient ß-acyloxy-oxametallacycles, which eliminate carboxylate to deliver allylic ruthenium(II) or osmium(II) alkoxides. Reduction of the metal(II) salt via hydrogen transfer from the secondary alcohol reactant releases the product of carbinol C-H vinylation and regenerates ketone and zero-valent catalyst.
Asunto(s)
Alcoholes/química , Ácidos Carboxílicos/química , Osmio/química , Rutenio/química , Compuestos de Vinilo/química , Catálisis , Complejos de Coordinación/química , HidrogenaciónRESUMEN
Ruthenium(II) complexes catalyze the CC coupling of 1,1-disubstituted allenes and fluorinated alcohols to form homoallylic alcohols bearing all-carbon quaternary centers with good to complete levels of diastereoselectivity. Whereas fluorinated alcohols are relatively abundant and tractable, the corresponding aldehydes are often not commercially available because of their instability.
Asunto(s)
Alcadienos/química , Carbono/química , Hidrocarburos Fluorados/síntesis química , Hidrógeno/química , Propanoles/síntesis química , Rutenio/química , Catálisis , Hidrocarburos Fluorados/química , Hidrogenación , Estructura Molecular , Oxidación-Reducción , Propanoles/química , EstereoisomerismoRESUMEN
Upon exposure to a ruthenium(0) catalyst, N-benzyl-3-hydroxy-2-oxindoles react with diverse alkynes to form products of C-H vinylation with complete control of regioselectivity and olefin geometry. This method contributes to a growing body of catalytic processes that enable direct conversion of lower alcohols to higher alcohols in the absence of stoichiometric organometallic reagents.
Asunto(s)
Alcoholes/química , Alquinos/química , Complejos de Coordinación/química , Oxindoles/química , Rutenio/química , Alquenos/química , Catálisis , Hidrogenación , Ligandos , Estructura Molecular , Oxidación-Reducción , Estereoisomerismo , TemperaturaRESUMEN
α-Olefins are the most abundant petrochemical feedstock beyond alkanes, yet their use in commodity chemical manufacture is largely focused on polymerization and hydroformylation. The development of byproduct-free catalytic C-C bond-forming reactions that convert olefins to value-added products remains an important objective. Here, we review catalytic intermolecular reductive couplings of unactivated and activated olefin-derived nucleophiles with carbonyl partners. These processes represent an alternative to the longstanding use of stoichiometric organometallic reagents in carbonyl addition.
RESUMEN
A Pd-catalyzed reaction of vinyl iodides and N-tosylhydrazones that assembles η(3)-allyl ligands through carbene insertion is demonstrated. Intramolecular trapping with nitrogen nucleophiles generates good yields of cinnamyl and pentadienyl amines like those found in alkaloid natural products. Carbenylative amination was the key reaction to complete the synthesis of the alkaloid caulophyllumine B. Migratory insertion was biased to provide allylamines with optical purity up to 64% ee, but in a lower yield.