A Boron–Boron Double Transborylation Strategy for the Synthesis of <i>gem</i>-Diborylalkanes

Docherty, Jamie H.; Nicholson, Kieran; Dominey, Andrew P.; Thomas, Stephen P.

doi:10.1021/acscatal.0c00869

Cited by 48 publications

(37 citation statements)

References 80 publications

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“…The extensive HBPin degradation observed in the presence of I / II at raised temperatures suggested that B–H species effective for catalyzing hydroboration may be formed in situ . Analysis of the decomposition of HBPin during catalysis using precatalyst II at 60, 90, and 110 °C (see the Supporting Information) revealed that although formation of (RO) 3 B species and 2,2-dimethyl-3-OBPin-butane is observed at all three temperatures it takes much longer at the two lower temperatures.…”

Section: Resultsmentioning

confidence: 99%

A Comparison of Two Zinc Hydride Catalysts for Terminal Alkyne C–H Borylation/Hydroboration and the Formation of 1,1,1-Triborylalkanes by Tandem Catalysis Using Zn–H and B–H Compounds

2020

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The synthesis of 1,1,1-triborylalkanes from terminal alkynes and pinacolborane (HBPin) is reported. This transformation proceeds via initial Zn-catalyzed alkyne C-H borylation, which can be achieved using a NacNacZnH complex. Combinations of a NacNacZn-alkynyl formed via C-H zincation of a terminal alkyne and HBPin exist in equilibrium with the alkynyl-BPin and NacNacZnH. The consumption of NacNacZnH by irreversible reaction with a terminal alkyne evolving H2 is essential for driving alkyne C-H borylation to completion. The alkynyl-BPin compounds undergo hydroboration catalyzed by Zn-H complexes at raised temperatures with a {7DIPP}ZnH(NTf2) complex (7DIPP = 1,3-bis(2,6-diisopropylphenyl)-4,5,6,7tetrahydro-1H-1,3-di-azepin-3-ium-2-ide) a more active catalyst for hydroboration than a NacNacZnH complex. Calculations indicate the {7DIPP}Zn-H congener has more pronounced biphilic character than NacNacZnH (greater electrophilicity at Zn while maintaining a sufficiently basic hydride). Of the two hydroboration steps, the hydroboration of alkynylBPin is catalyzed by Zn-H complexes, whilst the hydroboration of 1,1-diborylalkenes is catalyzed more effectively by B-H containing species, including boranes formed in-situ from HBPin. These observations led to a one-pot protocol being developed for converting terminal alkynes into 1,1,1-triborylalkanes that utilizes {7DIPP}ZnPh(NTf2) as a precatalyst for the formation of 1,1-diborylated alkenes with subsequent addition of BH3-THF as catalyst for the final step.

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Section: Resultsmentioning

confidence: 99%

A Comparison of Two Zinc Hydride Catalysts for Terminal Alkyne C–H Borylation/Hydroboration and the Formation of 1,1,1-Triborylalkanes by Tandem Catalysis Using Zn–H and B–H Compounds

2020

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“…Although, the barrier was lower than B−C(sp 3 )/B−H (28 kcal mol -1 ) transborylation. 32 The overall reaction was calculated to exergonic following H-B-9-BBN dimersation. 30,46 To translate the stoichiometric B−F transborylation to catalysis, the arylation of benzylic C−F bonds was investigated (Table 1).…”

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Borane-Catalyzed C(sp³)–F Bond Arylation and Esterification Enabled by Transborylation

2021

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The activation and functionalization of carbon-fluorine bonds represents a significant synthetic challenge given the high thermodynamic barrier to C-F bond cleavage. Stoichiometric hydridoborane-mediated C-F functionalization has recently emerged, but has yet to be rendered catalytic. Herein, the borane-catalyzed coupling of alkyl fluorides with arenes (carbon-carbon bond formation), and carboxylic acids (carbon-oxygen bond formation) has been developed using transborylation reactions to achieve catalytic turnover. Successful C-C and C-O coupling across a variety of structurally and electronically differentiated arenes and carboxylic acids was achieved using 9-borabicyclo[3.3.1]nonane (H-B-9-BBN) as the catalyst and pinacolborane (HBpin), with broad functional group tolerance. Experimental and computational studies suggest a mechanistic dichotomy for the carbon-carbon and carbon-oxygen coupling reactions. B-F transborylation (B−F/B−H metathesis) between F-B-9-BBN and HBpin enabled catalytic turnover for carbon-carbon bond formation whereas direct exchange between the alkyl fluoride and acyloxyboronic ester (C-F/B-O metathesis) was proposed for carbon-oxygen coupling, where H-B-9-BBN catalyzed the dehydrocoupling of the carboxylic acid with HBpin. ASSOCIATED CONTENTThis material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data (CIF) General experimental; system optimization; substrate synthesis; general reaction setup and procedure; product data; synthesis of reactive intermediates; single-turnover experiments; crystal data and experimental; computational details; NMR spectra; associated references (PDF)

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“…NaOH can be extracted with Et 2 O. Moreover, the generation of (pin)BOB(pin) [31] was confirmed when aq. NH 4 Cl instead of H 2 O was used for quenching; note that (pin)BOB(pin) cannot be extracted from an aq.…”

Section: Resultsmentioning

confidence: 85%

Stepwise Suzuki−Miyaura Cross‐Coupling of Triborylalkenes Derived from Alkynyl−B(dan)s: Regioselective and Flexible Synthesis of Tetrasubstituted Alkenes

et al. 2020

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Alkenes with three boryl groups of differing reactivities were synthesized and subsequently cross‐coupled regioselectively with aryl halides in a stepwise manner to afford tetrasubstituted alkenes. The key triborylalkene is derived from the platinum‐catalyzed diboration of alkynyl−B(dan)s with B2(pin)2. Due to excellent regioselectivity and reaction efficiency of each step starting with alkynyl−B(dan)s, tetrasubstituted alkenes with desired carbon frameworks at desired positions can be prepared in high yields. For example, an alkene with four distinct aryl groups, p‐MeOC6H4, p‐CF3C6H4, p‐MeC6H4, and p‐NCC6H4, was obtained in 71% overall yield via six steps, starting with the dehydrogenative borylation of p‐MeC6H4C≡CH with HB(dan). Moreover, a variety of tetrasubstituted alkenes, including regio‐ and stereoisomers of the above tetraarylalkene, AIE‐active TPTPE and derivatives thereof, and (Z)‐tamoxifen, a well‐known breast cancer drug, were accessed via the developed strategy.

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A Boron–Boron Double Transborylation Strategy for the Synthesis of gem-Diborylalkanes

Cited by 48 publications

References 80 publications

A Comparison of Two Zinc Hydride Catalysts for Terminal Alkyne C–H Borylation/Hydroboration and the Formation of 1,1,1-Triborylalkanes by Tandem Catalysis Using Zn–H and B–H Compounds

A Comparison of Two Zinc Hydride Catalysts for Terminal Alkyne C–H Borylation/Hydroboration and the Formation of 1,1,1-Triborylalkanes by Tandem Catalysis Using Zn–H and B–H Compounds

Borane-Catalyzed C(sp³)–F Bond Arylation and Esterification Enabled by Transborylation

Stepwise Suzuki−Miyaura Cross‐Coupling of Triborylalkenes Derived from Alkynyl−B(dan)s: Regioselective and Flexible Synthesis of Tetrasubstituted Alkenes

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A Boron–Boron Double Transborylation Strategy for the Synthesis of gem-Diborylalkanes

Cited by 48 publications

References 80 publications

A Comparison of Two Zinc Hydride Catalysts for Terminal Alkyne C–H Borylation/Hydroboration and the Formation of 1,1,1-Triborylalkanes by Tandem Catalysis Using Zn–H and B–H Compounds

A Comparison of Two Zinc Hydride Catalysts for Terminal Alkyne C–H Borylation/Hydroboration and the Formation of 1,1,1-Triborylalkanes by Tandem Catalysis Using Zn–H and B–H Compounds

Borane-Catalyzed C(sp3)–F Bond Arylation and Esterification Enabled by Transborylation

Stepwise Suzuki−Miyaura Cross‐Coupling of Triborylalkenes Derived from Alkynyl−B(dan)s: Regioselective and Flexible Synthesis of Tetrasubstituted Alkenes

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Borane-Catalyzed C(sp³)–F Bond Arylation and Esterification Enabled by Transborylation