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1. Recent advances in oxidative allylic C–H functionalization via group IX-metal catalysis

   https://doi.org/10.1039/D0CC05554A  

   Kazerouni, Amaan M.; McKoy, Quincy A.; Blakey, Simon B. (November 2020, Chemical Communications)

   null (Ed.)

   Allylic substitution, pioneered by the work of Tsuji and Trost, has been an invaluable tool in the synthesis of complex molecules for decades. An attractive alternative to allylic substitution is the direct functionalization of allylic C–H bonds of unactivated alkenes, thereby avoiding the need for prefunctionalization. Significant early advances in allylic C–H functionalization were made using palladium catalysis. However, Pd-catalyzed reactions are generally limited to the functionalization of terminal olefins with stabilized nucleophiles. Insights from Li, Cossy, and Tanaka demonstrated the utility of RhCp x catalysts for allylic functionalization. Since these initial reports, a number of key intermolecular Co-, Rh-, and Ir-catalyzed allylic C–H functionalization reactions have been reported, offering significant complementarity to the Pd-catalyzed reactions. Herein, we report a summary of recent advances in intermolecular allylic C–H functionalization via group IX-metal π-allyl complexes. Mechanism-driven development of new catalysts is highlighted, and the potential for future developments is discussed. 

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2. Stereospecific and Regioselective Synthesis of E -Allylic Alcohols through Reductive Cross Coupling of Terminal Alkynes

   https://doi.org/10.1021/jacs.3c06963  

   Shaff, Austin B; Yang, Langxuan; Lee, Mitchell T; Lalic, Gojko (November 2023, Journal of the American Chemical Society)

   We have developed a convergent method for the synthesis of allylic alcohols that involves a reductive coupling of terminal alkynes with α-chloro boronic esters. The new method affords allylic alcohols with excellent regioselectivity (anti-Markovnikov) and an E/Z ratio greater than 200:1. The reaction can be performed in the presence of a wide range of functional groups and has a substrate scope that complements the stoichiometric alkenylation of α-chloro boronic esters performed using alkenyl lithium and Grignard reagents. The transformation is stereospecific and allows for the robust and highly selective synthesis of chiral allylic alcohols. Our studies support a mechanism that involves hydrocupration of the alkyne and cross-coupling of the alkenyl copper intermediate with α-chloro boronic esters. Experimental evidence excludes a radical mechanism of the cross-coupling step and is consistent with the formation of a boron-ate intermediate and a 1,2-metalate shift. 

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3. Asymmetric intermolecular allylic C–H amination of alkenes with aliphatic amines

   https://doi.org/10.1126/science.abq1274  

   Pak Shing Cheung, Kelvin; Fang, Jian; Mukherjee, Kallol; Mihranyan, Andranik; Gevorgyan, Vladimir (December 2022, Science)

   Aliphatic allylic amines are found in a great variety of complex and biorelevant molecules. The direct allylic C–H amination of alkenes serves as the most straightforward method toward these motifs. However, use of widely available internal alkenes with aliphatic amines in this transformation remains a synthetic challenge. In particular, palladium catalysis faces the twin challenges of inefficient coordination of Pd(II) to internal alkenes but excessively tight and therefore inhibitory coordination of Pd(II) by basic aliphatic amines. We report a general solution to these problems. The developed protocol, in contrast to a classical Pd(II/0) scenario, operates through a blue light–induced Pd(0/I/II) manifold with mild aryl bromide oxidant. This open-shell approach also enables enantio- and diastereoselective allylic C–H amination. 

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4. Diastereoconvergent synthesis of anti -1,2-amino alcohols with N-containing quaternary stereocenters via selenium-catalyzed intermolecular C–H amination

   https://doi.org/10.1039/d2sc02648a  

   Zheng, Tianyi; Berman, Janna L.; Michael, Forrest E. (August 2022, Chemical Science)

   We report a diastereoconvergent synthesis of anti -1,2-amino alcohols bearing N-containing quaternary stereocenters using an intermolecular direct C–H amination of homoallylic alcohol derivatives catalyzed by a phosphine selenide. Destruction of the allylic stereocenter during the selenium-catalyzed process allows selective formation of a single diastereomer of the product starting from any diastereomeric mixture of the starting homoallylic alcohol derivatives, eliminating the need for the often-challenging diastereoselective preparation of starting materials. Mechanistic studies show that the diastereoselectivity is controlled by a stereoelectronic effect (inside alkoxy effect) on the transition state of the final [2,3]-sigmatropic rearrangement, leading to the observed anti selectivity. The power of this protocol is further demonstrated on an extension to the synthesis of syn -1,4-amino alcohols from allylic alcohol derivatives, constituting a rare example of 1,4-stereoinduction. 

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5. Regio- and Diastereoselective Synthesis of E -Allylic Amines through Hydroalkylation of Terminal Alkynes

   https://doi.org/10.1021/acscatal.4c00853  

   Wang, Bofei; Hazra, Avijit; Lalic, Gojko (April 2024, ACS Catalysis)

   Allylic amines make up an important class of organiccompounds that have inspired the development of numerous methods fortheir synthesis. One of the most effective transformations involves thecoupling of internal alkynes with appropriate nitrogen-containing electro-philes in the presence of a transition metal catalyst. We have developed amethod that allows transformation of terminal alkynes into allylic aminesthrough a copper-catalyzed reductive cross coupling with α-chloro phthalimides. The method has a broad substrate scope and resultsin the highly selective formation of the E-isomer of the anti-Markovnikov hydroamination product. A preliminary mechanistic studysupports a mechanism that involves the hydrocupration of the alkyne and the formation of a solvent-caged radical pair. 

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