We report a visible‐light‐mediated organocatalytic strategy for the enantioselective acyl radical conjugate addition to enals, leading to valuable 1,4‐dicarbonyl compounds. The process capitalizes upon the excited‐state reactivity of 4‐acyl‐1,4‐dihydropyridines that, upon visible‐light absorption, can trigger the generation of acyl radicals. By means of a chiral amine catalyst, iminium ion activation of enals ensures a stereoselective radical trap. We also demonstrate how the combination of this acylation process with a second catalyst‐controlled bond‐forming event allows to selectively access the full matrix of all possible stereoisomers of the resulting 2,3‐substituted 1,4‐dicarbonyl products.
The gold(I)-catalyzed cyclization of N-Boc-protected 6-alkynyl-3,4-dihydro-2H-pyridines, prepared by the Sonogashira coupling of lactam-derived enol triflates or phosphates, provides vinylogous amides, which are useful intermediates in the synthesis of natural compounds. The Au(I)-catalyzed reaction is carried out with Ph3PAuOTf as a catalyst and proceeds via a 6-endo-dig cyclization to form a vinylgold species that after protodeauration generates a cyclic carbamate intermediate. This intermediate is in most cases not isolated, but the addition of a base to the reaction mixture rapidly and quantitatively delivers the target vinylogous amide. The first synthesis of a natural compound from Sonneratia hainanensis has been accomplished by this approach.
Reported herein is av isible-light-mediated radical approach to the a-alkylation of ketones.T his method exploits the ability of anucleophilic organocatalyst to generate radicals upon S N 2-based activation of alkylh alides and blue light irradiation. The resulting open-shell intermediates are then intercepted by weakly nucleophilic silyl enol ethers,w hich would be unable to directly attackt he alkylh alides through at raditional two-electron path. The mild reaction conditions allowed functionalization of the a position of ketones with functional groups that are not compatible with classical anionic strategies.Inaddition, the redox-neutral nature of this process makes it compatible with ac inchona-based primary amine catalyst, whichw as used to develop ar are example of enantioselective organocatalytic radical a-alkylation of ketones.
We report av isible-light-mediated organocatalytic strategy for the enantioselective acyl radical conjugate addition to enals,l eading to valuable 1,4-dicarbonyl compounds.T he process capitalizes upon the excited-state reactivity of 4-acyl-1,4-dihydropyridines that, upon visible-light absorption, can trigger the generation of acyl radicals.B ym eans of ac hiral amine catalyst, iminium ion activation of enals ensures as tereoselective radical trap.W ea lso demonstrate howt he combination of this acylation process with as econd catalystcontrolled bond-forming event allows to selectively access the full matrix of all possible stereoisomers of the resulting 2,3substituted 1,4-dicarbonyl products.
Organic Near‐Infrared luminophores have found broad application as functional materials, but the development of efficient NIR emitters is still a challenging goal. Here we report on a new class of thieno[3,4‐b]pyrazine‐based NIR emitting materials with Aggregation Induced Emission (AIE) properties. The dyes feature a donor–acceptor–donor (D−A−D) structure, with a thienopyrazine acceptor core connected to two triarylamine donor groups bearing a tetraphenylethylene (TPE) moiety. Fast and efficient synthesis allowed the modular preparation of three dyes of tunable absorption and emission profiles. These constructs were extensively characterized by spectroscopic studies in different solvents, which revealed intense light‐harvesting ability and emissions in the deep‐red and NIR region with large Stokes shift values. Remarkably, the dyes exhibited AIE properties, retaining emissive ability in the aggregate state, thus emerging as attractive materials for their potential application in the development of luminescent devices.
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