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1. Diastereodivergent Synthesis of Bridged Tetrahydroisoquinoline Derivatives Catalyzed by Modularly Designed Organocatalysts

   https://doi.org/10.1002/adsc.202000227  

   Jakkampudi, Satish; Konda, Swapna; Arman, Hadi; Zhao, John_C‐G (April 2020, Advanced Synthesis & Catalysis)

   Abstract The diastereodivergent synthesis of bridged 1,2,3,4‐tetrahydroisoquinoline derivatives has been achieved by using appropriate modularly designed organocatalysts (MDOs) that are self‐assembled in situ from amino acids and cinchona alkaloid derivatives. The domino Mannich/aza‐Michael/aldol reaction between (E)‐2‐[2‐(3‐aryl‐3‐oxoprop‐1‐en‐1‐yl)phenyl]acetaldehydes and ethyl or benzyl (E)‐2‐[(4‐methoxyphenyl)imino]acetates catalyzed by MDOs gives two different diastereomers of the desired bridged tetrahydroisoquinolines in good yields and excellent diastereoselectivities (up to 99:1 dr) and enantioselectivities (up to >99%ee). The diastereodivergence was achieved in the aldol reaction step. magnified image 

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2. Borane‐Catalyzed Tandem Cyclization/Hydrosilylation Towards Enantio‐ and Diastereoselective Construction of trans ‐2,3‐Disubstituted‐1,2,3,4‐Tetrahydroquinoxalines

   https://doi.org/10.1002/anie.202305449  

   Luo, Zhenli; Li, Zhewei; Zhao, Haoqiang; Yang, Ji; Xu, Lijin; Lei, Ming; Fan, Qinghua; Walsh, Patrick J. (June 2023, Angewandte Chemie International Edition)

   Abstract Recent years have witnessed marked progress in the efficient synthesis of various enantioenriched 1,2,3,4-tetrahydroquinoxalines. However, enantio- and diastereoselective access to trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines remains much less explored. Herein we report that a frustrated Lewis pair-based catalyst generated via in situ hydroboration of 2-vinylnaphthalene with HB(C6F5)2 allows for the one-pot tandem cyclization/hydrosilylation of 1,2-diaminobenzenes and 1,2-diketones with commercially available PhSiH3 to exclusively afford trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines in high yields with excellent diastereoselectivities (>20 : 1 dr). Furthermore, this reaction can be rendered asymmetric by using an enantioenriched borane-based catalyst derived from HB(C6F5)2 and a binaphthyl-based chiral diene to give rise to enantioenriched trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines in high yields with almost complete diastereo- and enantiocontrol (>20 : 1 dr, up to >99 % ee). A wide substrate scope, good tolerance of diverse functionality and up to 20-gram scale production are demonstrated. The enantio- and diastereocontrol are achieved by the judicious choice of borane catalyst and hydrosilane. The catalytic pathway and the origin of the excellent stereoselectivity are elucidated by mechanistic experiments and DFT calculations. 

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3. Enantioselective regiospecific addition of propargyltrichlorosilane to aldehydes catalyzed by biisoquinoline N , N’ -dioxide

   https://doi.org/10.3762/bjoc.20.255  

   Brako, Noble; Narayanan, Sreerag Moorkkannur; Burns, Amber; Auter, Layla; Cesiliano, Valentino; Prabhakar, Rajeev; Takenaka, Norito (January 2024, Beilstein Journal of Organic Chemistry)

   Distilled propargyltrichlorosilane with >99% isomeric purity was prepared for the first time, and its asymmetric catalytic regiospecific addition reaction to aldehydes was developed through a systematic catalyst structure–reactivity and selectivity relationship study. The observed catalyst structure–enantioselectivity relationship of the present allenylation reaction was found exactly opposite to that of the analogous allylation reaction. The method provided eleven α-allenic alcohols in 22–99% yield with 61:39–92:8 enantiomeric ratios. Furthermore, possible mechanisms of propargyl–allenyl isomerization of propargyltrichlorosilane were computationally investigated. 

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4. Synthesis of oxaboranes via nickel-catalyzed dearylative cyclocondensation

   https://doi.org/10.1039/d2sc01840c  

   Koeritz, Mason T.; Banovetz, Haley K.; Prell, Sean A.; Stanley, Levi M. (July 2022, Chemical Science)

   We report Ni-catalyzed dearylative cyclocondensation of aldehydes, alkynes, and triphenylborane. The reaction is initiated by oxidative cyclization of the aldehyde and alkyne coupling partners to generate an oxanickelacyclopentene which reacts with triphenylborane to form oxaboranes. This formal dearylative cyclocondensation reaction generates oxaboranes in moderate-to-high yields (47–99%) with high regioselectivities under mild reaction conditions. This approach represents a direct and modular synthesis of oxaboranes which are difficult to access using current methods. These oxaboranes are readily transformed into valuable building blocks for organic synthesis and an additional class of boron heterocycles. Selective homocoupling forms oxaboroles, oxidation generates aldol products, and reduction and arylation form substituted allylic alcohols. 

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5. Al Incorporation up to 99% in Metalorganic Chemical Vapor Deposition‐Grown Monoclinic (Al _x Ga _1–x ) ₂ O ₃ Films Using Trimethylgallium

   https://doi.org/10.1002/pssr.202300224  

   Bhuiyan, A. F. M. Anhar Uddin; Meng, Lingyu; Huang, Hsien-Lien; Chae, Christopher; Hwang, Jinwoo; Zhao, Hongping (August 2023, physica status solidi (RRL) – Rapid Research Letters)

   Growths of monoclinic (Al_xGa_1−x)₂O₃thin films up to 99% Al contents are demonstrated via metalorganic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa) as the Ga precursor. The utilization of TMGa, rather than triethylgallium, enables a significant improvement of the growth rates (>2.5 μm h⁻¹) of β‐(Al_xGa_1−x)₂O₃thin films on (010), (100), and (01) β‐Ga₂O₃substrates. By systematically tuning the precursor molar flow rates, growth of coherently strained phase pure β‐(Al_xGa_1−x)₂O₃films is demonstrated by comprehensive material characterizations via high‐resolution X‐ray diffraction (XRD) and atomic‐resolution scanning transmission electron microscopy (STEM) imaging. Monoclinic (Al_xGa_1−x)₂O₃films with Al contents up to 99, 29, and 16% are achieved on (100), (010), and (01) β‐Ga₂O₃substrates, respectively. Beyond 29% of Al incorporation, the (010) (Al_xGa_1−x)₂O₃films exhibit β‐ to γ‐phase segregation. β‐(Al_xGa_1−x)₂O₃films grown on (01) β‐Ga₂O₃show local segregation of Al along (100) plane. Record‐high Al incorporations up to 99% in monoclinic (Al_xGa_1−x)₂O₃grown on (100) Ga₂O₃are confirmed from XRD, STEM, electron nanodiffraction, and X‐ray photoelectron spectroscopy measurements. These results indicate great promises of MOCVD development of β‐(Al_xGa_1−x)₂O₃films and heterostructures with high Al content and growth rates using TMGa for next‐generation high‐power and high‐frequency electronic devices. 

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