Conversion of Arylboronic Acids into Potassium Aryltrifluoroborates: Convenient Precursors of Arylboron Difluoride Lewis Acids

Vedejs, E.; Chapman, Richard W.; Fields, Stephen C.; Lin, Shuw-Guann; Schrimpf, Michael R.

doi:10.1021/jo00115a016

Cited by 439 publications

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“…5,[38][39][40][41][42] Especially organotrifluoroborates offer substantial benefits. They are air and moisture stable and can be easily prepared and purified; 5,43 however their use as substrates in Suzuki reactions is only marginally exploited. Herein, we report our recent results including ligand-free Suzuki cross-coupling reactions in aqueous media and within this context the utilization of potassium phenyltrifluoroborate as an alternative coupling partner.…”

Section: Introductionmentioning

confidence: 99%

Suzuki cross-coupling in aqueous media

et al. 2015

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We report a simple and efficient procedure for the ligand-free as well as ligand-assisted Suzuki reaction in both pure water and aqueous media. The cross-coupling reactions proceed successfully using phenylboronic acid or potassium phenyltrifluoroborate as a nucleophilic coupling partner. The method can be effectively applied to both activated and deactivated aryl halides yielding quantitative conversions. The catalytic activity of couplings performed in pure water increases when utilizing supramolecular additives, but decreases under standard phase-transfer conditions. Finally, the palladium loading is reducible from 3.0 mol% to 0.4 mol% without any loss of conversion.

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Section: Introductionmentioning

confidence: 99%

Suzuki cross-coupling in aqueous media

et al. 2015

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“…Next, all six hydroxyl groups were liberated. The two phenyl boronate moieties of 20 were removed with aqueous KHF 2 in methanol 40) to generate 21. Finally, the C13-acetate ester of 21 was chemoselectively saponified in the presence of the C3-ester using K 2 CO 3 in MeOH, and the C15-benzyl ether of 22 was detached using H 2 and Pd/C in MeOH, delivering ryanodine (1).…”

Section: )mentioning

confidence: 99%

Chemical Conversion of Ryanodol to Ryanodine

Masuda

Nagatomo

Inoue

2016

CHEMICAL & PHARMACEUTICAL BULLETIN

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Ryanodine (1) is a plant-derived natural product with powerful pharmacological and insecticidal action, and is a potent modulator of intracellular calcium release channels. Compound 1 possesses a 1H-pyrrole-2-carboxylate ester at the C3-position of heptahydroxylated terpenoid ryanodol (2). Whereas 2 was readily obtained from 1 by basic hydrolysis, 1 has never been synthesized from 2, due to the extreme difficulty in selectively introducing the bulky pyrrole moiety at the severely hindered C3-hydroxyl group of heptaol 2. Here we report chemical conversion of 2 to 1 for the first time. The derivatization was realized through the use of a new protective group strategy and the application of on-site construction of the pyrrole-2-carboxylate ester from the glycine ester and 1,3-bis(dimethylamino)allylium tetrafluoroborate.Key words acylation; protecting group; regioselectivity; ryanodine; terpenoid Ryanodine (1, Chart 1) has been isolated from the wood of Ryania speciosa VAHL and shown to possess potent insecticidal and pharmacological actions.1) Compound 1 binds specifically to a high-conductance intracellular calcium channel known as the ryanodine receptor (RyR), altering its conductance.2,3) Since the RyR plays an important role in many biological processes and malfunctions in its action have been linked to skeletal and cardiac diseases, 4-7) 1 has been used as a biological probe for investigations of RyR function, and is regarded as a strong candidate in the development of therapeutic agents for various diseases. [8][9][10] In 1968, the structure of ryanodine (1) was determined to be the ester between 1H-pyrrole-2-carboxylic acid (3) and the C3-hydroxyl group of ryanodol (2). [11][12][13][14] Compound 2 is a diterpenoid containing the exceedingly complex five fused rings (ABCDE-rings) with eleven contiguous stereocenters. Interestingly, the affinity of 2 toward RyRs of vertebrate skeletal muscle is 1700 times weaker than that of 1 (K D =7 nM), [15][16][17] demonstrating that the pyrrole group is a primary determinant for strong interactions of 1. Because of its important biological activities and intriguing structural features, many studies attempting the chemical construction of 1 has been carried out, which resulted in the total syntheses of ryanodol (2) by the Deslongchamps group in 1979 18,19) and by our laboratory in 2014. [20][21][22] In 1951, before the complete structure of 1 was known, Wiesner and colleagues found that basic hydrolysis of ryanodine (1) generated 2 and 3.11) However, the reverse reaction has not been realized even to date. The difficulty of the transformation arises from the need to control the regioselectivity of the four tertiary (C2, 4, 6, 12), two secondary (C3, 10) and one acetalic (C15) alcohols within heptaol 2 and to accommodate the bulky pyrrole moiety at the hindered C3-hydroxyl group. The computer-generated 23) structure of 2 revealed that its axially oriented C3-OH was shielded by the proximal C14-hydrogen atom and by the C19-, 20-methyl groups (Fig. 1). In fact, direct esteri...

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“…24 It was directly converted to the pull-fragment 7 with KHF 2 to benefit from increased stability, easier purification and higher reactivity of potassium trifluoroborates. [25][26][27] The push-fragment 8 was synthesized from phenol 24. The previously reported ortho-iodination gave pure regioisomer 25, 28 which was subjected to Williamson ether synthesis with tert-butyl bromoacetate 11.…”

Section: Figmentioning

confidence: 99%

Rigid-rod push–pull naphthalenediimide photosystems

et al. 2007

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Design, synthesis and evaluation of advanced rigid-rod pstack photosystems with asymmetric scaffolds are reported. The influence of push-pull rods on self-organization, photoinduced charge separation and photosynthetic activity is investigated and turns out to be surprisingly small overall.The design and synthesis of advanced optoelectric nanomaterials is a topic of current scientific interest. 1-18 In this report, we describe the synthesis and characteristics of push-pull p-octiphenyl 1, a rigid-rod molecule that carries blue naphthalenediimides (N,NNDIs) along the rigid-rod scaffold, a p-donating methoxy at one rod terminus and a p-accepting amide plus a negative charge at the other (Fig. 1). Compared to the previous photosystems 2 and 3, 16-18 the new push-pull rod 1 contains a macrodipole along the rigidrod scaffold. This axial macrodipole was of interest to explore the possibility of controlling photosynthetic and photophysical characteristics of 2 and 3 such as stabilization of the symmetrybreaking 2,16 photoinduced charge separation. These effects would be amplified with the parallel self-assembly of rod 1 into p-Mhelix 4. This supramolecule might form in lipid bilayers because of hindered translocation of the anionic carboxylate anchors across the membrane. In solution, dipole-dipole attraction should cause antiparallel self-assembly into quadruple p-M-helix 5 with reduced effects. These high expectations appeared meaningful considering the extensive evidence for remote control of optoelectric properties by a-helical macrodipoles. Highlights include fluorescence quenching in donor-acceptor dyads by a-helical dipoles, 19 amplified dark current along single a-helical dipoles, 20 and amplified photocurrents across monolayers of parallel ahelices on gold. 3 Moreover, rigid push-pull rods have been of use previously to create several variations of voltage-gated ion channels. 21, 22 The synthesis of rod 1 is summarized in Scheme 1. The psexiphenyl 6 was envisioned as an ideal building block to attach the p-attracting and p-donating rod termini 7 and 8, respectively, and the blue N,N-NDIs 9 along the rigid-rod scaffold. Rapid access to p-sexiphenyl 6 from the commercially available biphenyl 10 and tert-butyl bromoacetate 11 has been reported previously. 22 Last year, we also synthesized N,N-NDI 9 starting with oxidation of pyrene 12, reaction of the resulting dichlorodianhydride first with amines 13, 14 and then with 15 to give 16, followed by chemoselective removal of Alloc. 16 Rod terminus 7 was synthesized from benzaldehyde 17, which was converted into iodinated compound 18 in four steps. 23 After acidic deprotection, benzaldehyde 19 was reacted first with tertbutyl bromoacetate 11, followed by oxidation. Coupling of the resulting acid 20 with C-protected glycine 21 gave the desired p-accepting amide 22 with a protected carboxylate anchor. Pinacolboronate 23 was obtained by Pd-catalyzed conversion of aryl iodide 22. 24 It was directly converted to the pull-fragment 7 with KHF 2 to benefit from increased sta...

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Conversion of Arylboronic Acids into Potassium Aryltrifluoroborates: Convenient Precursors of Arylboron Difluoride Lewis Acids

Cited by 439 publications

References 0 publications

Suzuki cross-coupling in aqueous media

Suzuki cross-coupling in aqueous media

Chemical Conversion of Ryanodol to Ryanodine

Rigid-rod push–pull naphthalenediimide photosystems

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