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Barry M Trost - One of the best experts on this subject based on the ideXlab platform.
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broad spectrum enolate equivalent for catalytic chemo diastereo and enantioselective addition to n boc imines
ChemInform, 2016Co-Authors: Barry M Trost, Chaoi Joey HungAbstract:Alkynyl ketones are attractive but challenging nucleophiles in enolate chemistry. Their susceptibility to other reactions such as Michael additions and the difficulty of controlling the enolate geometry make them difficult substrates. Mannich-type reactions, which previously have not been reported using N-carbamoyl-imines with simple ketone Enolates, became our objective. In this report, we describe the first direct catalytic Mannich-type reaction between various ynones and N-Boc imines, whose stereocontrol presumably derives from catalyst control of enolate geometry. This method produces α-substituted β-amino ynones with excellent chemo-, diastereo-, and enantioselectivity. The products can be readily transformed into a broad range of molecular scaffolds upon further one-step transformations, demonstrating the utility of ynones as masked synthetic equivalents for a variety of unsymmetrically substituted acyclic ketones. In particular, alkynyl alkyl ketones resolve the long-standing problem of the inability to use the Enolates of unsymmetrical dialkyl ketones lacking α-branching for regio- and stereoselective reactions.
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Broad Spectrum Enolate Equivalent for Catalytic Chemo‑, Diastereo‑, and Enantioselective Addition to N‑Boc Imines
2015Co-Authors: Barry M Trost, Chao-i (joey) HungAbstract:Alkynyl ketones are attractive but challenging nucleophiles in enolate chemistry. Their susceptibility to other reactions such as Michael additions and the difficulty of controlling the enolate geometry make them difficult substrates. Mannich-type reactions, which previously have not been reported using N-carbamoyl-imines with simple ketone Enolates, became our objective. In this report, we describe the first direct catalytic Mannich-type reaction between various ynones and N-Boc imines, whose stereocontrol presumably derives from catalyst control of enolate geometry. This method produces α-substituted β-amino ynones with excellent chemo-, diastereo-, and enantioselectivity. The products can be readily transformed into a broad range of molecular scaffolds upon further one-step transformations, demonstrating the utility of ynones as masked synthetic equivalents for a variety of unsymmetrically substituted acyclic ketones. In particular, alkynyl alkyl ketones resolve the long-standing problem of the inability to use the Enolates of unsymmetrical dialkyl ketones lacking α-branching for regio- and stereoselective reactions
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palladium catalyzed decarboxylative asymmetric allylic alkylation of enol carbonates
Journal of the American Chemical Society, 2009Co-Authors: Barry M Trost, Jiayi Xu, Thomas SchmidtAbstract:Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio-, and enantioselective process for the synthesis of ketones bearing either a quaternary or a tertiary α-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic disubstituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium Enolates, the DAAA reaction proceeds through an “outer sphere” SN2 type of attack on the π-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium Enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the π-allylpalladium cation must serve as...
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palladium catalyzed decarboxylative asymmetric allylic alkylation of enol carbonates
Journal of the American Chemical Society, 2009Co-Authors: Barry M Trost, Thomas SchmidtAbstract:Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio-, and enantioselective process for the synthesis of ketones bearing either a quaternary or a tertiary alpha-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic disubstituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium Enolates, the DAAA reaction proceeds through an "outer sphere" S(N)2 type of attack on the pi-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium Enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the pi-allylpalladium cation must serve as the counterion for the enolate, the enolate probably exists as a tight-ion-pair. This largely prevents the common side reactions of Enolates associated with the equilibrium between different Enolates. The much milder reaction conditions as well as the much broader substrate scope also represent the advantages of the DAAA reaction over the direct allylation of preformed metal Enolates.
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palladium catalyzed asymmetric allylic α alkylation of acyclic ketones
Journal of the American Chemical Society, 2005Co-Authors: Barry M TrostAbstract:The first example of Pd-catalyzed asymmetric allyl alkylation of the conformationally nonrigid acyclic ketone Enolates is reported with excellent yields, regioselectivity, and enantioselectivity. The double bond geometry of the allyl enol carbonates affects its reactivity, selectivity, as well as the absolute configuration of the products. An opposite enantioselectivity from what is predicted by a direct attack of the enolate on the allyl moiety of the π-ally−Pd complex was observed. An alternative mechanism was proposed, which involves an inner sphere process of coordination of the enolate to Pd followed by reductive elimination.
Thomas Schmidt - One of the best experts on this subject based on the ideXlab platform.
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palladium catalyzed decarboxylative asymmetric allylic alkylation of enol carbonates
Journal of the American Chemical Society, 2009Co-Authors: Barry M Trost, Jiayi Xu, Thomas SchmidtAbstract:Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio-, and enantioselective process for the synthesis of ketones bearing either a quaternary or a tertiary α-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic disubstituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium Enolates, the DAAA reaction proceeds through an “outer sphere” SN2 type of attack on the π-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium Enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the π-allylpalladium cation must serve as...
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palladium catalyzed decarboxylative asymmetric allylic alkylation of enol carbonates
Journal of the American Chemical Society, 2009Co-Authors: Barry M Trost, Thomas SchmidtAbstract:Palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) of allyl enol carbonates as a highly chemo-, regio-, and enantioselective process for the synthesis of ketones bearing either a quaternary or a tertiary alpha-stereogenic center has been investigated in detail. Chiral ligand L4 was found to be optimal in the DAAA of a broad scope of cyclic and acyclic ketones including simple aliphatic ketones with more than one enolizable proton. The allyl moiety of the carbonates has been extended to a variety of cyclic or acyclic disubstituted allyl groups. Our mechanistic studies reveal that, similar to the direct allylation of lithium Enolates, the DAAA reaction proceeds through an "outer sphere" S(N)2 type of attack on the pi-allylpalladium complex by the enolate. An important difference between the DAAA reaction and the direct allylation of lithium Enolates is that in the DAAA reaction, the nucleophile and the electrophile were generated simultaneously. Since the pi-allylpalladium cation must serve as the counterion for the enolate, the enolate probably exists as a tight-ion-pair. This largely prevents the common side reactions of Enolates associated with the equilibrium between different Enolates. The much milder reaction conditions as well as the much broader substrate scope also represent the advantages of the DAAA reaction over the direct allylation of preformed metal Enolates.
Laura Raimondi - One of the best experts on this subject based on the ideXlab platform.
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optically active aminoalcohol promoted addition of 2 pyridylthioester boron Enolates to imines enantioselective one pot synthesis of β lactams
Tetrahedron, 1995Co-Authors: Rita Annunziata, Valentina Molteni, Mauro Cinquini, Franco Cozzi, Maurizio Benaglia, Laura RaimondiAbstract:Abstract The Enolates derived from 2-pyridylthioesters by treatment with BCl3·Me2S and enantiomerically pure aminoalcohols react with aromatic and heteroaromatic imines to afford β-lactams in a convenient one-pot procedure and in up to 78% e.e. The aminoalcohol can be employed both as the metal ligand and as the base to generate the enolate. Among several aminoalcohols tested, N-methylephedrine turned out to be the more efficient in terms of stereoselectivity.
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OPTICALLY-ACTIVE AMINOALCOHOL PROMOTED ADDITION OF 2-PYRIDYLTHIOESTER BORON Enolates TO IMINES - ENANTIOSELECTIVE ONE-POT SYNTHESIS OF BETA-LACTAMS
'Elsevier BV', 1995Co-Authors: Rita Annunziata, Valentina Molteni, Mauro Cinquini, Franco Cozzi, Maurizio Benaglia, Laura RaimondiAbstract:The Enolates derived from 2-pyridylthioesters by treatment with BCl3 . Me(2)S and enantiomerically pure aminoalcohols react with aromatic and heteroaromatic imines to afford beta-lactams in a convenient one-pot procedure and in up to 78% e.e. The aminoalcohol can be employed both as the metal ligand and as the base to generate the enolate. Among several aminoalcohols tested, N-methylephedrine turned our to be the more efficient in terms of stereoselectivity
Brian M Stoltz - One of the best experts on this subject based on the ideXlab platform.
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catalytic enantioselective synthesis of acyclic quaternary centers palladium catalyzed decarboxylative allylic alkylation of fully substituted acyclic enol carbonates
Journal of the American Chemical Society, 2018Co-Authors: Eric J Alexy, Haiming Zhang, Brian M StoltzAbstract:The first enantioselective palladium-catalyzed decarboxylative allylic alkylation of fully substituted acyclic enol carbonates providing linear α-quaternary ketones is reported. Investigation into the reaction revealed that the use of an electron-deficient phosphinooxazoline ligand renders the enolate geometry of the starting material inconsequential, with the same enantiomer of product obtained in the same level of selectivity regardless of the starting ratio of Enolates. As a result, a general method toward acyclic all-carbon quaternary stereocenters has been developed.
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Catalytic Enantioselective Synthesis of Acyclic Quaternary Centers: Palladium-Catalyzed Decarboxylative Allylic Alkylation of Fully Substituted Acyclic Enol Carbonates
2018Co-Authors: Eric J Alexy, Haiming Zhang, Brian M StoltzAbstract:The first enantioselective palladium-catalyzed decarboxylative allylic alkylation of fully substituted acyclic enol carbonates providing linear α-quaternary ketones is reported. Investigation into the reaction revealed that the use of an electron-deficient phosphinooxazoline ligand renders the enolate geometry of the starting material inconsequential, with the same enantiomer of product obtained in the same level of selectivity regardless of the starting ratio of Enolates. As a result, a general method toward acyclic all-carbon quaternary stereocenters has been developed
Frank Prechtl - One of the best experts on this subject based on the ideXlab platform.
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dimethyldioxirane oxidation of titanium Enolates diastereoselective alpha hydroxylations
Journal of Organic Chemistry, 1994Co-Authors: Waldemar Adam, Michael Mueller, Frank PrechtlAbstract:The oxidation of titanium Enolates, derived from a transmetalation reaction of the corresponding lithium Enolates with (i-PrO) 3 TiCl, (Et 2 N) 3 TiCl, or Cp 2 TiCl 2 , by dimethyldioxirane has been investigated. Furthermore, the diastereoselective hydroxylation of the chiral metal Enolates, e.g., derived from camphor (1f), menthone (1g), flavanone (1h), and 2-benzylcyclopentanone (1i), by dimethyldioxirane has been examined. The diastereoselectivity of the oxygen transfer strongly depends on the metal partner coordinated to the enolate. The titanium Enolates 4 resulted in much higher diastereoselectivities (up to 96% de) than the corresponding sodium Enolates 5 and at least as high if not higher than the silyl enol ethers 6. Moerover, the aldol reaction of ester-derived sodium Enolates with acetone, the unavoidable medium for dimethyldioxirane, could be totally suppressed by the use of the chlorotitanocene Enolates 4. Thus, the oxidation of chiral titanium Enolates by dimethyloxirane represents a general, convienient, effective, and chemo- and diastereoselective synthesis of α-hydroxy carbonyl compounds
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enantioselective oxidation of chiral titanium Enolates derived from propiophenone by dimethyldioxirane or 3 phenyl 2 phenylsulfonyloxazirdine
Chemische Berichte, 1994Co-Authors: Waldemar Adam, Frank PrechtlAbstract:The stereoselective oxidation of the optically active titanium enolate complexes 2 of propiophenone by dimethyldioxirane (3) (as acetone solution) and 3-phenyl-2-phenylsulfonyloxaziridine (4) has been investigated. The chiral titanium Enolates 2 were synthesized by the reaction of the lithium enolate of propiophenone and the respective optically active chlorotitanate complexes 1. For 3 as oxidant, the stereoselectivity of the a hydroxylation strongly depends on the substitution pattern at the central titanium atom and reached for the best case, namely 2e, an enantiometric excess (ee) of 63%. Solvent and temperature exhibited only small effects on the stereoselectivity. Compound 4 as oxidant gave lower enantiomeric excesses than 3
