- CONJUGATE ADDITION OF BENZYL COPPER REAGENTS TO α,β-ENOATES AND -ENONES.
-
Several benzylic copper reagents, BnCu(CN)MgCl, Bn2CuMgCl, BnCu-TMSCl-HMPA, and BnCu-TMSCl-TMEDA, facilitate the conjugate addition of the benzyl ligand to α,b-enones, but only BnCu-TMSCl-TMEDA gave high yields with α,β-unsaturated esters.
- Heerden, Pieter S. van,Bezuidenhoudt, Barend C. B.,Steenkamp, Jacobus A.,Ferreira, Daneel
-
-
Read Online
- A General Organocatalytic System for Enantioselective Radical Conjugate Additions to Enals
-
Herein, we report a general iminium ion-based catalytic method for the enantioselective conjugate addition of carbon-centered radicals to aliphatic and aromatic enals. The process uses an organic photoredox catalyst, which absorbs blue light to generate radicals from stable precursors, in combination with a chiral amine catalyst, which secures a consistently high level of stereoselectivity. The generality of this catalytic platform is demonstrated by the stereoselective interception of a wide variety of radicals, including non-stabilized primary ones which are generally difficult to engage in asymmetric processes. The system also served to develop organocatalytic cascade reactions that combine an iminium-ion-based radical trap with an enamine-mediated step, affording stereochemically dense chiral products in one-step.
- Le Saux, Emilien,Ma, Dengke,Bonilla, Pablo,Holden, Catherine M.,Lustosa, Danilo,Melchiorre, Paolo
-
supporting information
p. 5357 - 5362
(2021/02/01)
-
- Bioinspired Radical Stetter Reaction: Radical Umpolung Enabled by Ion-Pair Photocatalysis
-
A bioinspired, intermolecular radical Stetter reaction of α-keto acids and aldehydes is disclosed that is contingent on a formal “radical umpolung” concept. Enabled by secondary amine activation, electrostatic recognition ensures that the α-ketocarboxylic acids, which function as latent acyl radicals, are proximal to the in situ generated iminium salts. This photoactive contact ion pair is an electron donor–acceptor (EDA) complex, and undergoes facile single electron transfer (SET) and rapid decarboxylation prior to radical–radical recombination. Importantly, decarbonylation is mitigated by this strategy. The initial computational validation on which the process is predicated matches closely with experiment. Synergising organo- and photocatalysis activation principles finally expands the mechanistic and synthetic scope of the classic Stetter reaction to include α,β-unsaturated aldehydes as acceptors.
- Morack, Tobias,Mück-Lichtenfeld, Christian,Gilmour, Ryan
-
supporting information
p. 1208 - 1212
(2019/01/04)
-
- Direct Synthesis of Polysubstituted Aldehydes via Visible-Light Catalysis
-
Aldehydes are among the most versatile functional groups for synthetic chemistry. However, access to polysubstituted alkyl aldehydes is very limited and requires lengthy synthetic routes that involve multiple-step functional-group conversion. This paper reports a one-step synthesis of polysubstituted aldehydes from readily available olefin substrates using visible-light photoredox catalysis. Despite a number of competing reaction pathways, commercial styrenes react with vinyl ethers selectively in the presence of an acridinium salt photooxidant and a disulfide hydrogen-atom-transfer catalyst under blue LED irradiation. Alkyl aldehydes with different substitution patterns are prepared in good yields. This strategy can be applied to structurally sophisticated substrates.
- Wu, Fengjin,Wang, Leifeng,Chen, Jiean,Nicewicz, David A.,Huang, Yong
-
supporting information
p. 2174 - 2178
(2018/02/06)
-
- Scope and mechanism in palladium-catalyzed isomerizations of highly substituted allylic, homoallylic, and alkenyl alcohols
-
Herein we report the palladium-catalyzed isomerization of highly substituted allylic alcohols and alkenyl alcohols by means of a single catalytic system. The operationally simple reaction protocol is applicable to a broad range of substrates and displays a wide functional group tolerance, and the products are usually isolated in high chemical yield. Experimental and computational mechanistic investigations provide complementary and converging evidence for a chain-walking process consisting of repeated migratory insertion/β-H elimination sequences. Interestingly, the catalyst does not dissociate from the substrate in the isomerization of allylic alcohols, whereas it disengages during the isomerization of alkenyl alcohols when additional substituents are present on the alkyl chain.
- Larionov, Evgeny,Lin, Luqing,Gune, Laure,Mazet, Clment
-
supporting information
p. 16882 - 16894
(2015/01/09)
-