Organoboron Synthesis Research Articles

Enantioselective Synthesis of Organoborons Enabled by Cyclopropene Ring Opening

Enantioselective Synthesis of Organoborons Enabled by Cyclopropene Ring Opening

Enantioselective α-Boryl Carbene Transformations.

Carbenes, recognized as potent intermediates, enable unique chemical transformations, and organoborons are pivotal in diverse chemical applications. As a hybrid of carbene and the boryl group, α-boryl carbenes are promising intermediates for the construction of organoborons; unfortunately, such carbenes are hard to access and have low structural diversity with their asymmetric transformations largely uncharted. In this research, we utilized boryl cyclopropenes as precursors for the swift synthesis of α-boryl metal carbenes, a powerful category of intermediates for chiral organoboron synthesis. These α-boryl carbenes undergo a series of highly enantioselective transfer reactions, including B-H and Si-H insertion, cyclopropanation, and cyclopropanation/Cope rearrangement, catalyzed by a singular chiral copper complex. This approach opens paths to previously unattainable but easily transformable chiral organoborons, expanding both carbene and organoboron chemistry.

Radical hydroboration for the synthesis of organoboron compounds.

Organoboron compounds demonstrate diverse applications in the fields of organic synthesis, materials science, and medicinal chemistry. Compared to the conventional hydroboration reaction, radical hydroboration serves as an alternative approach for the synthesis of organoborons via different mechanisms. In radical hydroboration, a boryl radical is initially generated from homolytic cleavage of a B-H or a B-B bond, which is then added to an unsaturated double bond to deliver a carbon radical. Subsequent hydrogen atom transfer or reduction of the carbon radical to form a carbanion followed by protonation gave the final product. Over the past few years, numerous efforts have been made for efficient synthesis of boryl radicals and the expansion of substrate scope of the radical hydroboration reaction. Here, we discuss the recent advancement of radical hydroboration and its associated mechanisms. Numerous radical hydroboration strategies employing N-heterocyclic carbene borane, bis(pinacolato)diboron and pinacolborane as the boron source were illustrated. Thermochemical, photochemical and electrochemical strategies for the generation of boryl radicals were also discussed in detail.

Stereodefined polymetalloid alkenes synthesis via stereoselective boron-masking of polyborylated alkenes

Polyborylated-alkenes are valuable polymetalloid reagents in modern organic synthesis, providing access to a wide array of transformations, including the construction of multiple C–C and C–heteroatom bonds. However, because they contain similar boryl groups, many times their transformation faces the main challenge in controlling the chemo-, regio- and stereoselectivity. One way to overcome these limitations is by installing different boron groups that can provide an opportunity to tune their reactivity toward better chemo-, regio- and stereoselectivity. Yet, the preparation of polyborylated-alkenes containing different boryl groups has been rare. Herein we report concise, highly site-selective, and stereoselective boron-masking strategies of polyborylated alkenes. This is achieved by designed stereoselective trifluorination and MIDA-ation reactions of readily available starting polyborylated alkenes. Additionally, the trifluoroborylated-alkenes undergo a stereospecific interconversion to Bdan-alkenes. These transition-metal free reactions provide a general and efficient method for the conversion of polyborylated alkenes to access 1,1-di-, 1,2-di-, 1,1,2-tris-(borylated) alkenes containing BF3M, Bdan, and BMIDA, a family of compounds that currently lack efficient synthetic access. Moreover, tetraborylethene undergoes the metal-free MIDA-ation reaction to provide the mono BMIDA tetraboryl alkene selectively. The mixed polyborylalkenes are then demonstrated to be useful in selective C–C and C–heteroatom bond-forming reactions. Given its simplicity and versatility, these stereoselective boron-masking approaches hold great promise for organoboron synthesis and will result in more transformations.

Organoboron Compounds Towards Asymmetric Pericyclic Reaction; Exploitation to Bioactive Molecule Synthesis

AbstractOrganic frameworks containing boron as one of the units have wide application in organic synthesis. Due to the non‐toxicity and cheap accessibility, the organoboron compounds have gained increased demand towards the organic chemist. Besides, there has been a huge progress in the area of chiral organoboron synthesis, which allows direct access to chiral synthons. Among other methods developed for the asymmetric synthesis of organoboron compounds, pericyclic reaction plays an important role. Cycloaddition reactions using vinyl boronic esters have been extensively reported for the synthesis of cyclic boronic esters. Asymmetric cycloaddition using organoboron compound opens a quick access to various intermediates with multiple chiral centers, which has been utilized for the total synthesis of bioactive molecules. This mini‐review outlines various asymmetric pericyclic reactions developed to date demonstrating its applicability towards bioactive molecule synthesis.

Copper-Catalyzed Ring-Opening/Borylation of Cyclopropenes

Copper-Catalyzed Ring-Opening/Borylation of Cyclopropenes

Stereoselective Diels-Alder Reactions of gem-Diborylalkenes: Toward the Synthesis of gem-Diboron-Based Polymers.

Although gem-diborylalkenes are known to be among the most valuable reagents in modern organic synthesis, providing a rapid access to a wide array of transformations, including the construction of C–C and C-heteroatom bonds, their use as dienophile-reactive groups has been rare. Herein we report the Diels–Alder (DA) reaction of (unsymmetrical) gem-diborylalkenes. These reactions provide a general and efficient method for the stereoselective conversion of gem-diborylalkenes to rapidly access 1,1-bisborylcyclohexenes. Using the same DA reaction manifold with borylated-dienes and gem-diborylalkenes, we also developed a concise, highly regioselective synthesis of 1,1,2-tris- and 1,1,3,4-tetrakis(boronates)cyclohexenes, a family of compounds that currently lack efficient synthetic access. Furthermore, DFT calculations provided insight into the underlying factors that control the chemo-, regio-, and stereoselectivity of these DA reactions. This method also provides stereodivergent syntheses of gem-diborylnorbornenes. The utility of the gem-diborylnorbornene building blocks was demonstrated by ring-opening metathesis polymerization (ROMP), providing a highly modular approach to the first synthesis of the gem-diboron-based polymers. Additionally, these polymers have been successfully submitted to postpolymerization modification reactions. Given its simplicity and versatility, we believe that this novel DA and ROMP approach holds great promise for organoboron synthesis as well as organoboron-based polymers and that it will result in more novel transformations in both academic and industrial research.

New Radical Borylation Pathways for Organoboron Synthesis Enabled by Photoredox Catalysis

AbstractRadical borylation using N‐heterocyclic carbene (NHC)‐BH3 complexes as boryl radical precursors has emerged as an important synthetic tool for organoboron assembly. However, the majority of reported methods are limited to reaction modes involving carbo‐ and/or hydroboration of specific alkenes and alkynes. Moreover, the generation of NHC‐boryl radicals relies principally on hydrogen atom abstraction with the aid of radical initiators. A distinct radical generation method is reported, as well as the reaction pathways of NHC‐boryl radicals enabled by photoredox catalysis. NHC‐boryl radicals are generated via a single‐electron oxidation and subsequently undergo cross‐coupling with the in‐situ‐generated radical anions to yield gem‐difluoroallylboronates. A photoredox‐catalyzed radical arylboration reaction of alkenes was achieved using cyanoarenes as arylating components from which elaborated organoborons were accessed. Mechanistic studies verified the oxidative formation of NHC‐boryl radicals through a single‐electron‐transfer pathway.

New Radical Borylation Pathways for Organoboron Synthesis Enabled by Photoredox Catalysis.

Radical borylation using N-heterocyclic carbene (NHC)-BH3 complexes as boryl radical precursors has emerged as an important synthetic tool for organoboron assembly. However, the majority of reported methods are limited to reaction modes involving carbo- and/or hydroboration of specific alkenes and alkynes. Moreover, the generation of NHC-boryl radicals relies principally on hydrogen atom abstraction with the aid of radical initiators. A distinct radical generation method is reported, as well as the reaction pathways of NHC-boryl radicals enabled by photoredox catalysis. NHC-boryl radicals are generated via a single-electron oxidation and subsequently undergo cross-coupling with the in-situ-generated radical anions to yield gem-difluoroallylboronates. A photoredox-catalyzed radical arylboration reaction of alkenes was achieved using cyanoarenes as arylating components from which elaborated organoborons were accessed. Mechanistic studies verified the oxidative formation of NHC-boryl radicals through a single-electron-transfer pathway.

Photoredox-Catalysed New Radical Borylation Pathways for Organoboron Synthesis

Photoredox-Catalysed New Radical Borylation Pathways for Organoboron Synthesis

Synthetic Transformations of Alkenyl MIDA Boronates toward the Efficient Construction of Organoborons

The attachment of N-methyliminodiacetyl boron (MIDA boron) to alkenes leads to a new type of activated alkenes. Synthetic manipulation of the alkene double bond while retaining the boron moiety offers an unprecedented opportunity for the construction of organoborons. These reactions feature unique reactivity, good regioselectivity, and they can be used to access organoborons that are historically difficult to prepare. Herein, we give a brief summary of advances in the use of alkenyl MIDA boronates as starting materials for organoboron synthesis. Mechanisms are discussed where relevant.

Hajime Ito

Angewandte Chemie International EditionVolume 57, Issue 23 p. 6733-6733 Author ProfileFree Access Hajime Ito First published: 05 January 2018 https://doi.org/10.1002/anie.201712526AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract “I can never resist the temptation of spicy food. The best advice I have ever been given is love what you do, and do your best ...” This and more about Hajime Ito can be found on page 6733. Hajime Ito The author presented on this page has recently published his 10th article in Angewandte Chemie in the last 10 years: “Synthesis of Acylborons by Ozonolysis of Alkenylboronates: Preparation of an Enantioenriched Amino Acid Acylboronate”: J. Taguchi, T. Ikeda, R. Takahashi, I. Sasaki, Y. Ogasawara, T. Dairi, N. Kato, Y. Yamamoto, J. W. Bode, H. Ito, Angew. Chem. Int. Ed. 2017, 56, 13847; Angew. Chem. 2017, 129, 14035. Date of birth: March 11, 1968 Position: Professor, Division of Applied Chemistry, Graduate School of Engineering, Hokkaido University E-mail: hajito@eng.hokudai.ac.jp Homepage: http://labs.eng.hokudai.ac.jp/labo/organoelement/?lang=en ORCID: 0000-0003-3852-6721 Education: 1991 BS (Eng) Kyoto University 1996 PhD with Prof. Yoshihiko Ito, Kyoto University 2001 Research Associate with Prof. Kim D. Janda, The Scripps Research Institute, La Jolla Awards: 2011 The President's Research Award, Hokkaido University; 2014 The Chemical Society of Japan Award for Creative Work; 2016 Fujifilm Corporation Award in Synthetic Organic Chemistry, Japan Current research interests: Development of new reactions for organic synthesis; design of molecular crystalline materials and their phase transitions; mechanoresponsive materials If I were not a scientist, I would be a historian. My favorite place on earth is my home, Sapporo. My top three films of all time are Gladiator, Castle in the Sky, and Seven Samurai. My favorite food is Tonkatsu (Japanese deep-fried pork cutlets). My favorite quote is “Do your best in your research. Do not think your students are bad when their research did not go well” (the late Professor Yoshihiko Ito). The most significant scientific advance of the last 100 years has been the development of semiconductors and computers. If I could have dinner with three famous scientists from history, they would be Archimedes, Alexander Fleming, and Michael Faraday. My best investment was when I was a student, I tried to maintain a broad sense of curiosity. I think that was an important investment that helps my current research. My worst nightmare was a dream in which I was chased by a horde of zombies who used to be my neighbors in my hometown. Guaranteed to make me happy is talking with students about their new findings and future ideas. My 5 top papers: 1“Boration of an α,β-enone using a diboron promoted by a copper(I)–phosphine mixture catalyst”: H. Ito, H. Yamanaka, J. Tateiwa, A. Hosomi, Tetrahedron Lett. 2000, 41, 6821. (The first reported copper(I)-catalyzed borylation, which later turned to be a very powerful tool in organoboron synthesis.) 2“Mechanical stimulation and solid seeding trigger single-crystal-to-single-crystal molecular domino transformations”: H. Ito, M. Muromoto, S. Kurenuma, S. Ishizaka, N. Kitamura, H. Sato, T. Seki, Nat. Commun. 2013, 4, 2009. (A small mechanical stress can induce an entire single-crystal phase change, as well as a variation in luminescent properties.) 3“Controlling Mechano- and Seeding-Triggered Single-Crystal-to-Single-Crystal Phase Transition: Molecular Domino with a Disconnection of Aurophilic Bonds”: T. Seki, K. Sakurada, H. Ito, Angew. Chem. Int. Ed. 2013, 52, 12828; Angew. Chem. 2013, 125, 13062. (Mechanical picking can induce a molecular-level structural change in a crystal.) 4“Synthesis of Optically Active Boron-Silicon Bifunctional Cyclopropane Derivatives through Enantioselective Copper(I)-Catalyzed Reaction of Allylic Carbonates with a Diboron Derivative”: H. Ito, Y. Kosaka, K. Nonoyama, Y. Sasaki, M. Sawamura, Angew. Chem. Int. Ed. 2008, 47, 7424; Angew. Chem. 2008, 120, 7534. (These borylative cyclization and carboborylation reactions provide access to cyclopropane structures, which are important for drug discovery.) 5“Enantioselective Synthesis of Chiral Piperidines via the Stepwise Dearomatization/Borylation of Pyridines”: K. Kubota, Y. Watanabe, K. Hayama, H. Ito, J. Am. Chem. Soc. 2016, 138, 4338. (This borylation reaction can be used to form many optically active boron compounds from readily available pyridine derivatives.) Volume57, Issue23June 4, 2018Pages 6733-6733 ReferencesRelatedInformation

Progresses on the Application of Stable Borane Adducts in the Synthesis of Organoborons

Progresses on the Application of Stable Borane Adducts in the Synthesis of Organoborons

Ni and Pd mediate asymmetric organoboron synthesis with ester functionality at the β-position

Catalytic systems based on Ni and Pd complexes modified with chiral P-P ligands can be used in a convenient strategy for enantioselectively adding a boron unit to the beta-position of alpha,beta-unsaturated esters.

Catalytic asymmetric boron–boron addition to unsaturated molecules

Abstract In this paper, we present representative examples of metal-catalyzed asymmetric boron–boron addition to C C and describe chiral organoboron synthesis as a suitable method for preparing chiral-functionalized compounds.