ABSTRACT
An enantioselective hydroaminoalkylation of azaaryl ketones under a transition-metal-free asymmetric photoredox catalysis platform is reported. A series of valuable azaarene-functionalized 1,2-amino alcohols featuring attractive quaternary carbon stereocenters have been synthesized in high yields with good to excellent enantioselectivities. The viability of readily accessible N-aryl glycines as reaction partners facilitates the conjugate modification of these products into important derivatives, thereby enhancing the synthetic utility of the current approach.
ABSTRACT
An enantioselective radical alkylation of 4-alkyl-1,4-dihydropyridines with Morita-Baylis-Hillman (MBH) adducts has been reported. The SN2-type products are predominant. This reaction is enabled by dual photoredox/palladium catalysis. The alkylation products are provided in good yields with good regio- and enantioselectivity. The use of Ding's spiroketal-based bis(phosphine) (SKP) ligand is crucial to achieving satisfactory regio- and enantioselectivity. The resultant α,ß-unsaturated ester can be easily reduced to a synthetically useful chiral allyl alcohol.
ABSTRACT
The first catalytic asymmetric photoreduction of 1,2-diketones and α-keto ketimines under visible light irradiation is reported. A transition-metal-free synergistic catalysis platform harnessing dicyanopyrazine-derived chromophore (DPZ) as the photoredox catalyst and a non-covalent chiral organocatalyst is effective for these transformations. With the flexible use of a chiral Brønsted acid or base in H+ transfer interchange to control the elusive enantioselective protonation, a variety of chiral α-hydroxy ketones and α-amino ketones were obtained with high yields and enantioselectivities.
ABSTRACT
Reported herein is the first example of 2-allylazaarenes in asymmetric catalysis. Highly γ-selective allylation was demonstrated for activated ketones, including isatins and trifluoromethyl ketones. In the presence of either an amino-acid-based tertiary amine or quaternary ammonium salt catalyst, two series of tertiary hydroxy-containing moieties were installed at the remote δ-position of azaarenes in good chemical yields, excellent enantioselectivities, and E/Z ratios. The success of current γ-selective reactions should provide inspiration for expansion to other allylazaarene derivatives and would open up new paradigms for the synthesis of chiral γ- and/or δ-functionalized azaarenes.
ABSTRACT
Reported is a rationally-designed one-pot sequential strategy that allows homoallylic alcohols to be employed in a catalytic, asymmetric, direct vinylogous aldol reaction with a series of activated acyclic ketones, including trifluoromethyl ketones, γ-ketoesters, and α-keto phosphonates, in high yields (up to 95%) with excellent regio- and enantio-selectivity (up to 99% ee). This modular combination, including Jones oxidation and asymmetric organocatalysis, has satisfactory compatibility and reliability even at a 20 mmol scale, albeit without intermediary purification.
Subject(s)
Alcohols/chemical synthesis , Chemistry Techniques, Synthetic , Aldehydes/chemistry , Catalysis , Ketones/chemistryABSTRACT
The first catalytic asymmetric vinylogous aldol reaction of activated allyls to activated acyclic ketones is disclosed. A variety of activated acyclic ketones, such as trifluoromethyl ketones, α-ketoesters, and α-keto phosphonates, were found to be involved forming diverse γ-selective aldol adducts with high enantioselectivities (up to >99% ee). The method provides an effective, general strategy to access valuable chiral electron-withdrawing group-substituted tertiary hydroxyl-based carboxylic acids.
ABSTRACT
An L-amino acid based urea-tertiary amine-catalyzed enantioselective stereoablative carboxylation of 3-bromooxindoles with malonic acid half thioesters (MAHTs) and diverse commercially available carboxylic acids has been developed. A series of valuable 3-substituted 3-hydroxy-2-oxindoles were obtained in high enantioselectivities (up to 93% ee). This chemoselective reaction represents the first example of MAHTs as carboxylating agents.