Gotowa bibliografia na temat „Regioselective Hydroboration”

Simple, commercially available borane adducts, H3B·THF and H3B·SMe2, have been used to catalyse the hydroboration of alkynes and alkenes with pinacolborane to give the alkenyl and alkyl boronic esters, respectively. Alkynes and terminal alkenes underwent highly regioselective hydroboration to give the linear boronic ester products. Good functional group tolerance was observed for substrates bearing ester, amine, ether and halide substituents. This catalytic process shows comparable reactivity to transition-metal-catalysed hydroboration protocols.

A new, efficient synthesis of racemic cyclopent-3-en-1-yl nucleoside analogues has been developed starting from cyclopentadiene. The key step is the regioselective hydroboration of an intermediately formed mixture of two alkylated cyclopentadienes to give one cyclopentenol. The remaining double bond was further functionalized by hydroboration, epoxidation, cis-hydroxylation and cyclopropanation.

A series of novel structural magnesium(i) complexes stabilized by cyclopentyl and cyclohexyl substituted β-diketiminate ligands have been synthesized and used as highly active and regioselective pre-catalysts for various epoxides hydroboration.

Boronic acid(esters) have been well recognized as an indispensable coupling partner in the Suzuki-Miyaura cross coupling reactions producing a vast spectrum of molecules, applicable in the diverse field ranging from medicinal to materials sciences.[1] Transition metal catalyzed synthesis of boronic esters from diborons with the assistance of bases is a well-established methodology[2]. In this thesis, the cobalt-N-Heterocyclic carbene complexes catalyzed borylation of organic compounds and interaction of diazabutadienes with diboron compounds will be discussed. (i) In the first section, Co(IMes)2Cl2 catalyzed borylation of aryl halides will be discussed. [3a] The robust protocol, operating under mild condition facilitate the borylation of a diverse range of aryl halides with great efficacy, which includes the challenging aryl chlorides. The preliminary mechanistic studies suggest that base-bis(pinacolato)diboron adduct reduces the Co(IMes)2Cl2 complex to generate Co(IMes)2Cl complex, which acts as an active catalytic species. (ii) The second section deals with catalytic synthesis of primary and secondary alkyl boronic esters using alkyl halides. [3b] The in situ generated Co-NHC complex, in assistance with base and diboron compound, produces the corresponding borylated product from alky halides. The reaction proceeds under very mild conditions and covers a wide range of alkyl halides, including chlorides having different functional groups. (iii) In the third section, development in selective hydroboration of vinyl arenes and aliphatic alkenes will be discussed. [3c] Catalyzed by Co(I)NHC complex, the alkene hydroboration by pinacol borane gives Markovnikov selective product with good selectivity, where the regio-selectivity is controlled by phenyl substituent. In absence of that, complete inversion in the selectivity has been observed. The preliminary mechanistic cycle suggests that the catalytic cycle proceeds via oxidative addition of pinacol borane to [Co] followed by alkene insertion and reduction elimination steps. (iv) The last section discusses the interaction of diazabutadiene molecules with diboron compounds. [3d] The diazabutadiene derivatives have been observed to completely cleave the B-B bond of Bis(catacolato)diboron and Bis(dithiocatacolato)diboron. The preliminary findings hint towards homolytic cleavage of the B-B bond by concerted interaction of the two nitrogen atoms of diazabutadiene with the two boron atoms of the diboron from the same face. References: [1] Boronic Acids-Preparation and Applications in Organic Synthesis, Medicine and Materials, 2nd ed.; Hall, D. G., Ed.; Wiley-VCH: Weinheim, 2011. [2] Neeve, E. C.; Geier, S. J.; Mkhalid, I. A. I.; Westcott, S. A.; Marder, T. B. Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse. Chem. Rev. 2016, 116, 9091-9161. [3] (a) Verma, P. K.; Mandal, S.; Geetharani, K. ACS Catal. 2018, 8, 4049-4054. (b) Verma, P. K.; Prasad, K. S.; Varghese, D.; Geetharani, K. Org. Lett. 2020, 22, 4, 1431-1436. (c) Verma, P. K.; Setulekshmi, A. S.; Geetharani, K. Org. Lett. 2018, 20, 7840-7845. (d) Verma, P. K.; Meher, N. K.; Geetharani, K. Accepted for publication in Chem. Commun., Manuscript ID: CC-COM-06-2021-002881.R2.

In the context of ongoing efforts toward C-aryl glycoside synthesis, a recently developed approach to form C-aryl glycals from 2-deoxysugar lactones was expanded to form novel substrates. This approach has been applied to the synthesis of various furyl glycals, allowing access to C-aryl glycals via a benzyne furan (4+2) cycloaddition methodology. The hydroboration-oxidation of said C-aryl glycals has allowed access to C(2)-oxygenated C-aryl glycosides via the benzyne cycloaddition approach. An approach to the total synthesis of 5-hydoxyaloin A is detailed, in which regioselective benzyne furan (4+2) cycloadditions were achieved via the use of a silicon tether. Two approaches to the anthrone core have been applied; one in which an unsymmetrically-substituted aryl ring is first constructed by means of a silicon tether, and one in which the unsymmetrically-substituted ring is formed last, also utilizing a silicon tether. The latter approach has allowed access to the anthrone core of 5-hydroxyaloin A, and only a final desulfurization remains in order to access the natural product.
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Paul J. Chirik at Princeton University reported (Science 2012, 335, 567) an iron catalyst that hydrosilylates alkenes with anti-Markovnikov selectivity, as in the conversion of 1 to 2. A regioselective hydrocarbamoylation of terminal alkenes was developed (Chem. Lett. 2012, 41, 298) by Yoshiaki Nakao at Kyoto University and Tamejiro Hiyama at Chuo University, which allowed for the chemoselective conversion of diene 3 to amide 4. Gojko Lalic at the University of Washington reported (J. Am. Chem. Soc. 2012, 134, 6571) the conversion of terminal alkenes to tertiary amines, such as 5 to 6, with anti-Markovnikov selectivity by a sequence of hydroboration and copper-catalyzed amination. Related products such as 8 were prepared (Org. Lett. 2012, 14, 102) by Wenjun Wu at Northwest A&F University and Xumu Zhang at Rutgers via an isomerization-hydroaminomethylation of internal olefin 7. Seunghoon Shin at Hanyang University (experimental work) and Zhi-Xiang Yu at Peking University (computational work) reported (J. Am. Chem. Soc. 2012, 134, 208) that 9 could be directly converted to bicyclic lactone 11 with propiolic acid 10 using gold catalysis. A nickel/Lewis acid multicatalytic system was found (Angew. Chem. Int. Ed. 2012, 51, 5679) by the team of Professors Nakao and Hiyama to effect the addition of pyridones to alkenes, such as in the conversion of 12 to 13. Radical-based functionalization of alkenes using photoredox catalysis was developed (J. Am. Chem. Soc. 2012, 134, 8875) by Corey R.J. Stephenson at Boston University, an example of which was the addition of bromodiethyl malonate across alkene 14 to furnish 15. Samir Z. Zard at Ecole Polytechnique reported (Org. Lett. 2012, 14, 1020) that the reaction of xanthate 17 with terminal alkene 16 led to the product 18. The radical-based addition of nucleophiles including azide to alkenes with Markovnikov selectivity (cf. 19 to 20) was reported (Org. Lett. 2012, 14, 1428) by Dale L. Boger at Scripps La Jolla using an Fe(III)/NaBH4-based system. A remarkably efficient and selective catalyst 22 was found (J. Am. Chem. Soc. 2012, 134, 10357) by Douglas B. Grotjahn at San Diego State University for the single position isomerization of alkenes, which effected the transformation of 21 to 23 in only half an hour.

Vinyl glycine 2 is a useful precursor to a variety of amino acids. Timothy E. Long of the University of Georgia found (Tetrahedron Lett. 2009, 50, 5067) that the o-nitrophenyl sulfoxide 1 eliminated smoothly in refluxing toluene. Alicia Boto and Rosendo Hernández of IPNA La Laguna observed (Tetrahedron Lett. 2009, 50, 3974) that a related selenoxide elimination proceeded to give the single regioisomer 4. Avelino Corma of the Universidad Politécnica de Valencia developed ( Chemical Commun. 2009, 4947) a gold catalyst for the selective hydroboration of alkynes over alkenes. Eiji Shirakawa and Tamio Hayashi of Kyoto University devised (Chemical Commun. 2009, 5088) a Ru catalyst for the conversion of an alkenyl triflate such as 8 to the corresponding bromide. Tristan H. Lambert of Columbia University found (J. Am. Chem. Soc. 2009, 131, 13930) that the dichloride 11 smoothly converted a variety of alcohols into the corresponding chlorides. Crown ethers have been used to promote SN2 reactivity by solubilizing the metal cation. Sungyul Lee of Kyunghee University, Dae Yoon Chi of Sogang University, and Choong Eui Song of Sungkyunkwan University demonstrated (Angew. Chem. Int. Ed. 2009, 48, 7683) that the inexpensive polyethylene glycols were also effective. Mugio Nishizawa of Tokushima Bunri University devised (Synlett 2009, 1175) conditions for the rapid regioselective hydration of hydroxy alkynes such as 15. Jaume Vilarrasa of the Universitat de Barcelona developed (Organic Lett. 2009, 11, 4414) a mild alternative protocol for the Nef reaction, converting a nitroalkane such as 17 into the corresponding ketone under neutral conditions. Clément Mazet of the University of Geneva optimized (Tetrahedron Lett. 2009, 50, 4141) the Ir-catalyzed conversion of an allylic alcohol 19 into the saturated aldehyde. Jonathan M. J. Williams of the University of Bath established (Angew. Chem. Int. Ed. 2009, 48, 7375) that under Ir-catalyzed “borrowing hydrogen” conditions, alkyl amines could donate alkyl groups to anilines such as 21. Danfeng Huang and Yulai Hu of Northwest Normal University devised (Organic Lett. 2009, 11, 4474) a simple protocol for conversion of an acid 23 to the Weinreb amide 24. of the Universitat

Swadeshmukul Santra of the University of Central Florida described (Tetrahedron Lett. 2009, 50, 124) a simple preparation of silica nanoparticles that efficiently catalyzed the anti-Markovnikov addition of thiophenol to alkenes (illustrated) and also to alkynes. Akiya Ogawa of Osaka Prefecture University devised (Tetrahedron Lett. 2009, 50, 624) a protocol for the photoinduced hydrophosphinylation of an alkene 3 to the phosphine oxide 4. Xavi Ribas and Miquel Costas of the University of Girona developed (Adv. Synth. Cat. 2009, 351, 348) a manganese catalyst for the epoxidation of alkenes with 30% H2O2. Masahito Ochiai of the University of Tokushima established (J. Am. Chem. Soc. 2009, 131, 1382) an iodoarene-catalyzed oxidation of an alkene 7 to the keto acid 9. If, as is likely, isolated alcohols are stable under these conditions, this will be a useful complement to RuO4 cleavage. Several methods are available for homologating unactivated alkenes. Sven Doye of the Universität Oldenburg observed (Angew. Chem. Int. Ed. 2009, 48, 1153) that a Ti catalyst could effect the addition of N-methyl aniline 10 to the alkene 3, to give the branched product 11 . The reaction also worked well in an intramolecular sense. Note that in this process, a C-H bond is also converted to a C-C bond. Kiyoshi Tomioka of Kyoto University reported (Organic Lett. 2009, 11, 2007) that the Suzuki coupling of the hydroboration product from 12 with the iodo alkene 13 was best supported by AsPh3. Teck-Peng Loh of Nanyang Technological University showed (J. Am. Chem. Soc. 2009, 131, 1372) that the homologation of an isolated alkene 15 with an acrylate ester 16 could also be carried out under oxidative conditions to give the diene 17. Weiping Su of the Fujian Institute of Research on the Structure of Matter found (Organic Lett. 2009, 11, 2341) that similar oxidative conditions effected the decarboxylative addition of an aromatic acid such as 18 to an alkene to give the substituted styrene 19. Kian L. Tan of Boston College took advantage (Organic Lett. 2009, 11, 2764) of a chelating ligand to direct the regioselective hydroformylation of an allylic sulfonamide 20. Isolated internal alkenes were stable under these conditions.