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1. 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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2. 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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3. Metal‐Ligand Cooperativity to Assemble a Neutral and Terminal Niobium Phosphorus Triple Bond (Nb≡P)

   https://doi.org/10.1002/anie.202212488  

   Senthil, Shuruthi; Kwon, Seongyeon; Fehn, Dominik; Im, Hoyoung; Gau, Michael R.; Carroll, Patrick J.; Baik, Mu‐Hyun; Meyer, Karsten; Mindiola, Daniel J. (November 2022, Angewandte Chemie International Edition)

   Abstract Decarbonylation along with P‐atom transfer from the phosphaethynolate anion, PCO⁻, to the Nb^IVcomplex [(PNP)NbCl₂(N^tBuAr)] (1) (PNP=N[2‐PⁱPr₂‐4‐methylphenyl]₂⁻; Ar=3,5‐Me₂C₆H₃) results in its coupling with one of the phosphine arms of the pincer ligand to produce a phosphanylidene phosphorane complex [(PNPP)NbCl(N^tBuAr)] (2). Reduction of2with CoCp*₂cleaves the P−P bond to form the first neutral and terminal phosphido complex of a group 5 transition metal, namely, [(PNP)Nb≡P(N^tBuAr)] (3). Theoretical studies have been used to understand both the coupling of the P‐atom and the reductive cleavage of the P−P bond. Reaction of3with a two‐electron oxidant such as ethylene sulfide results in a diamagnetic sulfido complex having a P−P coupled ligand, namely [(PNPP)Nb=S(N^tBuAr)] (4). 

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4. The Trajectory of the (η 5-Cyclopentadienyl)cobalt-Mediated Cycloisomerization of Ene-Yne-Ene-Type Allyl Propargylic Ethers to Furans: A DFT Appraisal

   https://doi.org/10.1055/a-1645-2632  

   Wong, Jonathan J.; Chen, Xiangyang; Houk, Kendall N.; Vollhardt, K. Peter (October 2021, Synthesis)

   Abstract The mechanisms by which the complexes CpCoL2 (Cp = C5H5; L = CO or CH2=CH2) mediate the cycloisomerizations of α,δ,ω-enynenes containing allylic ether linkages are probed by DFT methods. The outcomes corroborate experimental results and provide energetic and structural details of the trajectories leading to 3-(oxacyclopentyl or cycloalkyl)furans via the intermediacy of isolable CpCo-η 4-dienes. They comprise initial stereoselective complexation of one of the double bonds and the triple bond, rate-determining oxidative coupling to a triplet 16e cobalta-2-cyclopentene, and terminal double bond docking, followed by stereocontrolled insertion to assemble intermediate cis- and trans-fused triplet cobalta-4-cycloheptenes. A common indicator of the energetic facility of the latter is the extent of parallel alignment of the alkene moiety and its target Co–Cα bond. The cobalta-4-cycloheptenes transform further by β-hydride elimination–reductive elimination to furnish CpCo-η 4-dienes, which are sufficiently kinetically protected to allow for their experimental observation. The cascade continues through cobalt-mediated hydride shifts and dissociation of the aromatic furan ring. The findings in silico with respect to the stereo-, regio-, and chemoselectivity are in consonance with those obtained in vitro. 

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5. Development of regiodivergent asymmetric reductive coupling reactions of allenamides to access heteroatom-rich organic compounds

   https://doi.org/10.1039/D3CC03013J  

   Collins, Stephen; Sieber, Joshua D (August 2023, Chemical Communications)

   This feature article describes the application ofN-substituted allenes in regiodivergent reductive coupling strategies in the context of new methods for the synthesis of heteroatom-rich organic compounds. 

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