Intramolecular Aminoboration of Unfunctionalized Olefins

Yang, Chunhua; Zhang, Yushi; Fan, Wei; Liu, Gong‐Qing; Li, Yue‐Ming

doi:10.1002/anie.201505489

Cited by 52 publications

(26 citation statements)

References 47 publications

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“…2.5 %C H 3 Cl was formed by 1 HNMR spectroscopy). The3 2ppm 11 Bc hemical shift is consistent with an equilibrium between the Lewis adduct and free BCl 3 and anisole.T hus anisole binding to BCl 3 is reversible and ether cleavage is not significant at 20 8 8C, suggesting that alkyne borylative cyclization using BCl 3 is viable.…”

supporting

confidence: 62%

“…[17] While ether cleavage of anisoles with BBr 3 is well documented, detailed studies into the mechanism are rare, [19] but one recent report calculated that PhOÀMe cleavage is ab imolecular process involving two Me(Ph)OÀBBr 3 moieties. [19a] Thus B may be prearranged to undergo rapid ether cleavage and other oalkynyl anisoles may be less prone to ether cleavage, particularly using BCl 3 instead of BBr 3 .C onsistent with this the combination of equimolar anisole and BCl 3 in DCM at 20 8 8Cr esulted in the formation of as ingle 11 Br esonance at 32 ppm with minimal ether cleavage observed even after 30 h at 20 8 8C( only ca. 2.5 %C H 3 Cl was formed by 1 HNMR spectroscopy).…”

mentioning

confidence: 96%

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BCl₃‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes

et al. 2016

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BCl3‐induced borylative cyclization of aryl‐alkynes possessing ortho‐EMe (E=S, O) groups represents a simple, metal‐free method for the formation of C3‐borylated benzothiophenes and benzofurans. The dichloro(heteroaryl)borane primary products can be protected to form synthetically ubiquitous pinacol boronate esters or used in situ in Suzuki–Miyaura cross couplings to generate 2,3‐disubstituted heteroarenes from simple alkyne precursors in one pot. In a number of cases alkyne trans‐haloboration occurs alongside, or instead of, borylative cyclization and the factors controlling the reaction outcome are determined.

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supporting

confidence: 62%

mentioning

confidence: 96%

BCl₃‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes

et al. 2016

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“…Demethylation furnishes thioboric ester 10 ; subsequent B–S bond addition across the alkyne yields product 2 , which is a known pathway for several other B–X σ bond addition reactions. [29–32] In order to examine the thiophilicity of ClBcat toward 1a at ambient temperature, the initial reaction mixture was evaluated by NMR spectroscopy in d 8 -toluene. 1 H and 11 B NMR spectra obtained at t = 0 at ambient temperature showed no evidence of sulfur coordination to boron as judged by persistence resonances corresponding to starting material 1a and ClBcat and the absence of other resonances.…”

Section: Mechanistic Studies: Boron As a Thiophilic Or Carbophilic Lementioning

confidence: 99%

Catalyst‐Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes

et al. 2016

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The first ring-forming thioboration reaction of C–C π bonds is reported. This catalyst-free method proceeds in the presence of a commercially available external electrophilic boron source (B-chlorocatecholborane) in good to high yields. The method is scalable and tolerates a variety of functional groups that are intolerant of other major borylation methods. The resulting borylated benzothiophenes participate in a variety of in situ derivatization reactions, showcasing that these borylated intermediates do not need to be isolated prior to downstream functionalization. This methodology has been extended to the synthesis of borylated dihydrothiophenes. Mechanistic experiments suggest that the operative mechanistic pathway is through boron-induced activation of the alkyne followed by electrophilic cyclization, as opposed to S–B σ bond formation, providing a mechanistically distinct pathway to the thioboration of C–C π bonds.

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“…Demethylation furnishes thioboric ester 10; subsequent B-S bond addition across the alkyne yields product 2, which is a known pathway for several other B-X σ bond addition reactions. [29][30][31][32] In order to examine the thiophilicity of ClBcat toward 1a at ambient temperature, the initial reaction mixture was evaluated by NMR spectroscopy in d 8 -toluene. 1 H and 11 B NMR spectra obtained at t = 0 at ambient temperature showed no evidence of sulfur coordination to boron as judged by persistence resonances corresponding to starting material 1a and ClBcat and the absence of other resonances.…”

Section: Mechanistic Studies: Boron As a Thiophilic Or Carbophilic Lementioning

confidence: 99%

Catalyst‐Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes

et al. 2016

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The first ring-forming thioboration reaction of C-C π bonds is reported. This catalyst-free method proceeds in the presence of a commercially available external electrophilic boron source (Bchlorocatecholborane) in good to high yields. The method is scalable and tolerates a variety of functional groups that are intolerant of other major borylation methods. The resulting borylated benzothiophenes participate in a variety of in situ derivatization reactions, showcasing that these borylated intermediates do not need to be isolated prior to downstream functionalization. This methodology has been extended to the synthesis of borylated dihydrothiophenes. Mechanistic experiments suggest that the operative mechanistic pathway is through boron-induced activation of the alkyne followed by electrophilic cyclization, as opposed to S-B σ bond formation, providing a mechanistically distinct pathway to the thioboration of C-C π bonds. Borylative CyclizationsThe first ring-forming thioboration reaction of C-C π bonds is reported. The resulting borylated benzothiophenes participate in a variety of in situ derivatization reactions, showcasing that these borylated intermediates do not need to be isolated prior to downstream functionalization. Mechanistic experiments suggest that the operative mechanistic pathway is through boron-induced activation of the alkyne followed by electrophilic cyclization. KeywordsBoron; C-C Activation; Sulfur Heterocycles; Sulfur; Cyclization Thioboration, the addition of sulfur and boron across C-C π bonds, holds promise as an efficient route to synthesize functionalized thioethers. [1] This area of research has focused on Correspondence to: Suzanne A. Blum. HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript reagents containing B-S σ bonds that are capable of adding in a direct fashion to π systems. In 2015, Bo, Fernández, and Westcott demonstrated the ability of B-S σ bonds from inhouse synthesized reagents to add across Michael acceptors through boron activation of the carbonyl oxygen (Figure 1a, top), but without generation of a B-C bond for downstream functionalization. [2] In 1993, Miyaura and Suzuki developed a thioboration reaction of B-S σ bonds across alkynes. [3,4] This method similarly employed in-house synthesized reagents containing B-S σ bonds, however it used a carbophilic palladium catalyst to activate the C-C π bond. Protodeboration and in situ Suzuki cross-coupling reactions of these thioboration products were demonstrated, establishing the utility of such synthetic intermediates ( Figure 1a, bottom).In contrast, formal thioboration, wherein the equivalents of boron and sulfur add across a C-C π bond, is underexplored, despite the potential advantages of employing commercially available boron reagents as opposed to the thioboration reagents requiring synthesis, and the plausibility of avoiding a palladium catalyst as previously required in the direct thioboration of alkynes. [3,4] Although little is known about the thiophilicity versus ca...

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Intramolecular Aminoboration of Unfunctionalized Olefins

Cited by 52 publications

References 47 publications

BCl₃‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes

BCl₃‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes

Catalyst‐Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes

Catalyst‐Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes

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Intramolecular Aminoboration of Unfunctionalized Olefins

Cited by 52 publications

References 47 publications

BCl3‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes

BCl3‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes

Catalyst‐Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes

Catalyst‐Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes

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BCl₃‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes

BCl₃‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes