297746-06-6Relevant academic research and scientific papers
Enantioselective decarboxylative alkylation reactions: Catalyst development, substrate scope, and mechanistic studies
Behenna, Douglas C.,Mohr, Justin T.,Sherden, Nathaniel H.,Marinescu, Smaranda C.,Harned, Andrew M.,Tani, Kousuke,Seto, Masaki,Ma, Sandy,Novak, Zoltan,Krout, Michael R.,McFadden, Ryan M.,Roizen, Jennifer L.,Enquist Jr., John A.,White, David E.,Levine, Samantha R.,Petrova, Krastina V.,Iwashita, Akihiko,Virgil, Scott C.,Stoltz, Brian M.
supporting information; experimental part, p. 14199 - 14223 (2012/02/01)
α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center. Sly as a PHOX: The development of an enantioselective decarboxylative palladium-catalyzed allylic alkylation reaction, utilizing phosphinooxazoline ligands, is described. The catalyst is applied to a range of allyl enol carbonate, silyl enol ether, and allyl β-ketoester substrates to provide alkylated ketone products in excellent yield and good ee (see scheme). The utility of these products is demonstrated by their use in several asymmetric syntheses. Mechanistic studies are reported suggesting an unusual inner-sphere mechanism. Copyright
Acetylene - Dicobaltcarbonyl complexes with chiral phosphinooxazoline ligands: Synthesis, structural characterization, and application to enantioselective intermolecular Pauson-Khand reactions
Castro, Jaume,Moyano, Albert,Pericas, Miquel A.,Riera, Antoni,Alvarez-Larena, Angel,Piniella, Joan F.
, p. 7944 - 7952 (2007/10/03)
The reaction of the phenylacetylene - dicobalthexacarbonyl complex (2) with the 4-R-2-(2-diphenylphosphinophenyl)oxazolines 1 (R = Ph) and 4 (R = CH2CH2SCH3) leads to the selective formation of the chelated complexes 3 and 5, respectively. On the other hand, the tert-butyl-substituted phosphinooxazoline 6 acts as a monodentate ligand, and its reaction with several 1-alkyne-derived complexes (2,7 - 10) affords readily separable mixtures of the diastereomer nonchelated complexes 11a,b - 15a,b. The interconversion rate between diastereomeric pairs is dependent on the steric bulk of the alkyne substituent, and neither 3 nor 5 epimerize at room temperature. The structures of both kinds of complexes have been ascertained by a combination of spectroscopical (IR, NMR), X-ray diffraction, and chiroptical methods; this has allowed the development of a practical procedure for the establishment of the absolute configuration of the chiral alkyne - dicobaltcarbonyl complexes obtained by the selective substitution of a carbon monoxide on one of the diastereotopic cobalt atoms. The intermolecular Pauson - Khand reaction of the chelated complexes 3 and 5 with norbornadiene respectively affords the (+) and (-) enantiomers of expected enone adduct 25, but in low enantiomeric excesses. Contrary to that, the tertiary amine N-oxide-promoted intermolecular Pauson - Khand reactions of nonchelated complexes 11a,b - 13a,b give the corresponding norbornadiene- or norbornene-derived adducts both in high yields (85-99%) and enantioselectivities (93-97% enantiomeric excess), in what constitutes a substantial improvement over preexisting procedures for this reaction. The possibility of achieving chiral induction in the Pauson - Khand reaction of symmetrical alkynes (via the corresponding dicobaltpentacarbonyl complexes with ligand 6) has been demonstrated for the first time. An enantioselectivity mnemonic rule and a mechanistic model that explains the observed asymmetric sense of induction have been developed, and have been found to be in agreement with the results of model semiempirical molecular orbital calculations.
