NHC and visible light-mediated photoredox co-catalyzed 1,4-sulfonylacylation of 1,3-enynes for tetrasubstituted allenyl ketones

Abstract

The modulation of selectivity of highly reactive carbon radical cross-coupling for the construction of C-C bonds represents a challenging task in organic chemistry. N-Heterocyclic carbenes (NHCs) catalyzed radical transformations opened...

Radical transformations for allene synthesis

“…53 Moreover, the energy for the enantiodetermining transition states TS A_B(R) is 1.8 kcal/mol lower than that of TS A_B(S) . In addition, when using chiral NHCs as the catalysts, the groups of Huang 38 and Zhang 40 have independently studied the asymmetric coupling of allenyl radicals with the ketyl radicals (Scheme 29). In Please do not adjust margins Please do not adjust margins…”

“…Very recently, Zhang et al revealed a NHCs and visible light-mediated photoredox co-catalyzed radical 1,4-sulfonylacylation of 1,3-enynes ( Scheme 19 ). 40 The optimization of a range of NHC catalysts and photocatalysts found that the emerge of NHC-2 and [Ir(ppy) 2 (dtbbpy)]PF 6 was the best choice for this transformation and the dimerized product can be greatly suppressed. Instead of using aldehydes as the carbonyl source, aroyl fluorides was turned out to be good precursors for the generation of ketyl radicals via oxidative quenching process of excited photocatalysis.…”

Research Progress on N-Heterocyclic Carbene Catalyzed Reactions for Synthesizing Ketones through Radical Mechanism

“…36 When olefins were replaced by 1,3-enynes, the Zhang group demonstrated that 1,4-sulfonylacylation occurred to provide tetrasubstituted allenyl ketones without the elimination of the sulfonyl group as for 1,2-sulfonylacylation (Scheme 25). 37 Scheme 24 Direct -acylation of alkenes via NHC, sulfinate, and photoredox cooperative triple catalysis 36…”

Visible Light‐Mediated Manipulation of 1,n‐Enynes in Organic Synthesis

“…Impressively, a dual Ir-photoredox/NHC-catalysed 1,4-sulfonylation of 1,3-enyne 1 for the synthesis of tetrasubstituted allenyl ketones 27 was accomplished by Zheng, Zhang, and coworkers by the reaction between 1,3-enynes 1, aroyl fluorides 26, and sodium sulfonylates 21 (Scheme 9). [34] This protocol displayed a broad functional group tolerance and afforded the A very interesting synthesis of sulfonyl allenic alcohols 30 was discovered by Wu and co-workers from the reaction between vinyl enyne 28 as a substrate, sulfonyl chloride 29 as a sulfonyl radical precursor, and K 3 PO 4 as a base under visible light irradiation (Scheme 10). [35] The reaction, surprisingly, demonstrated water splitting using sulfonyl chlorides in the presence of a base, likely involving a proton-coupled electron transfer (PCET) step and trapping of the allenic radical by the resulting sulfonyl radical.…”

“…Impressively, a dual Ir‐photoredox/NHC‐catalysed 1,4‐sulfonylation of 1,3‐enyne 1 for the synthesis of tetrasubstituted allenyl ketones 27 was accomplished by Zheng, Zhang, and co‐workers by the reaction between 1,3‐enynes 1 , aroyl fluorides 26 , and sodium sulfonylates 21 (Scheme 9). [34] This protocol displayed a broad functional group tolerance and afforded the desired products 27 in 40–98 % yield. Experimental studies reveal that the key step involved in this protocol is the radical cross‐coupling between allenyl 9 D and the ketyl radical intermediate 9 B .…”