Traditionally, indanones were prepared from the corresponding indenols or indenones. With this HRS strategy in mind, we engaged to develop practical approaches for important scaffolds synthesis via a radical pathway.Ĭonsidering the prevalence of indanones and their derivatives in pharmaceuticals and biologically active natural products 31, 32, 33, 34, 35, a lot of efforts have been devoted to developing effective strategies for indanones synthesis 36, 37, 38, 39, 40. Importantly, this would be another complementary process to that of PS catalysis. To the best of our knowledge, no successful examples utilizing this strategy have been reported. Notably, the core difference between HRS-promoted HAT and that of polarity-reversal-catalyzed 29, 30 is that hydrogen radical transfer occurs from a neutral position to another non-radical site. Based on the great achievements in PS catalysis, we wondered whether a similar hydrogen radical-shuttle (HRS) strategy could be used to complete the HAT process (Fig. In the latter process (hydrogen radical transfer), a reactive radical species, traditionally, was needed to abstract hydrogen from C–H bond to generate the corresponding carbon-centered radical intermediate 6, 7, 8, 11, 25, 26, 27, 28, triggering the following functionalization process. It has been recognized that PS catalysts, such as water 16, acid 13, 17, 18, 19, 20, 21, 22, 23 and alcohol 24, could lower the reaction barrier by forming cyclic molecular complexes that involve lower ring strain and facilitate intra- or intermolecular HAT. When it comes to proton transfer, proton-shuttle (PS) catalysis has been well developed for the past decades, providing a highly efficient strategy for C–H functionalization, especially in transition-metal-catalyzed C–H activation 13, 14, 15 and insertion of carbenes into heteroatom–hydrogen bonds 16, 17, 18, 19, 20, 21, 22, 23, 24 (Fig. Importantly, this mechanistically distinctive HAT provides a complement to that of typical proton-shuttle-promoted, representing a breakthrough in hydrogen radical transfer, especially in the inherently challenging 1,2- or 1,3-HAT.Īs a powerful and effective strategy, hydrogen atom transfer (HAT) catalysis has been demonstrated as an ideal platform for C–H bonds functionalizations, majorly involving proton shift and hydrogen radical transfer 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. Critical to the success of this process is the introduction of water, acting as both HRS and hydrogen source, which was demonstrated by mechanistic experiments and density functional theory (DFT) calculations. This protocol features broad substrate scope, excellent functional group tolerance, internal hydrogen radical transfer, atom- and step-economy. In this work, a HRS-enabled decarboxylative annulation of carbonyl compounds via photoredox catalysis for the synthesis of indanones is developed. Compared to proton-shuttle process, which is well established for organic synthesis, hydrogen radical-shuttle (HRS) is unexplored. However, intramolecular 1,n (n = 2 or 3)-HAT is very challenging due to slow kinetics. Intramolecular 1,n (n = 5 or 6)-HATs are common and frequently encountered in organic synthesis. Hydrogen atom transfer (HAT) process is a powerful and effective strategy for activating C-H bonds followed by further functionalization.
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