<i>trans</i>‐Hydroboration of Propargyl Alcohol Derivatives and Related Substrates

Longobardi, Lauren E.; Fürstner, Alois

doi:10.1002/chem.201902228

Cited by 30 publications

(18 citation statements)

References 85 publications

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“…In most cases, excellent isomeric purity was reached, bearing witness of the strong directing effect of the benzo-1,3,2-diazaborininone ring system. In line with previous experiences with trans-hydrometalations, branching at the propargylic position tends to decrease the regioselectivity, [14,16] as manifested in the results obtained with the cyclopentyl and the cyclohexyl derivatives 10 a and 12, respectively; gratifyingly though, the samples were enriched by flash chromatography in the desired alpha,trans-isomers 11 a and 13, respectively,. Alternatively, one can resort to the use of the fluorinated anthranilamide derivative 10 b, which provides another solution to this problem: the comparison of entries 6 and 7 confirms the notion that the fluorinated boron-heterocycle exerts a stronger directing effect.…”

Section: Improved Synthesis Of Alkynyl-b(aam) Derivatives and Investigation Into The Scope Of The Reactionsupporting

confidence: 89%

Regioselective trans‐Hydrostannation of Boron‐Capped Alkynes

Melot

Saiegh

Fürstner

2021

Chemistry A European J

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Alkynyl‐B(aam) (aam=anthranilamidato) derivatives are readily available bench‐stable compounds that undergo remarkably selective reactions with Bu3SnH in the presence of [Cp*RuCl]4 as the catalyst. The addition follows a stereochemically unorthodox trans‐selective course; in terms of regioselectivity, the Bu3Sn‐ unit is delivered with high fidelity to the C‐atom of the triple bond adjacent to the boracyclic head group (“alpha,trans‐addition”). This outcome is deemed to reflect a hydrogen bonding interaction between the protic −NH groups of the benzo‐1,3,2‐diazaborininone ring system and the polarized [Ru−Cl] bond in the loaded catalyst, which locks the substrate in place in a favorable orientation relative to the incoming reagent. The resulting isomerically (almost) pure gem‐dimetalated building blocks are amenable to numerous downstream functionalizations; most remarkable is the ability to subject the −B(aam) moiety to Suzuki‐Miyaura cross coupling without need for prior hydrolysis while keeping the adjacent Bu3Sn‐ group intact. Alternatively, the tin residue can be engaged in selective tin/halogen exchange without touching the boron substituent; the fact that the two ‐NH entities of −B(aam) do not protonate organozinc reagents and hence do not interfere with Negishi reactions of the alkenyl halides thus formed is another virtue of this so far underutilized boracycle. Overall, the ruthenium catalyzed trans‐hydrostannation of alkynyl‐B(aam) derivatives opens a practical gateway to isomerically pure trisubstituted alkenes of many different substitution patterns by sequential functionalization of the 1‐alkenyl‐1,1‐heterobimetallic adducts primarily formed.

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Section: Improved Synthesis Of Alkynyl-b(aam) Derivatives and Investigation Into The Scope Of The Reactionsupporting

confidence: 89%

Regioselective trans‐Hydrostannation of Boron‐Capped Alkynes

Melot

Saiegh

Fürstner

2021

Chemistry A European J

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“…Thus, diphenylacetylene ( 2r ) was treated with H–B(dan) in the presence of 1g to furnish 1,2-addition product 3r in 96% yield ( E / Z = 30:70) (Scheme ). This result reveals promising potential for the development of metal-catalyzed trans -hydroborations of diarylalkynes that would complement the existing trans -hydroborations of internal alkynes. ,− …”

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confidence: 88%

Ruthenium-Catalyzed (Z)-Selective Hydroboration of Terminal Alkynes with Naphthalene-1,8-diaminatoborane

et al. 2019

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The metal-catalyzed (Z)-selective hydroboration of terminal alkynes is synthetically challenging due to the usually (E)-selective nature of the hydroboration and the formation of the thermodynamically unstable (Z)-isomer. Herein, we report that N-heterocyclic-carbene-ligated ruthenium complexes catalyze the (Z)-selective hydroboration of terminal alkynes with H–B(dan) (dan = naphthalene-1,8-diaminato), which generates a diverse range of synthetically valuable (Z)-alkenylboranes. Mechanistic studies, particularly the isolation of a catalytically relevant borylruthenium complex, revealed a mechanism that involves the insertion of the alkyne into a Ru–B bond, which provides a catalytic cycle that is distinctly different from that of previously reported (Z)-selective hydroborations. The direct cross-coupling of the obtained (Z)-alkenyl-B(dan) enables the rapid synthesis of biologically active Combretastatin A-4 analogues.

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“…For example, canonical hydroboration of unbiased internal alkynes suffers from substantial regioselectivity issues. Recent efforts directed toward the stereoselective preparation of trisubstituted alkenylboron compounds are depicted in Scheme and range from the Ru-catalyzed formal trans -hydroboration reactions systems (Scheme a), ,− to stereoselective elimination reactions (Scheme b) and boron-Wittig reactions (Scheme c) . Alternative approaches utilize alkene isomerization to establish the regio- and stereochemistry of the alkenylboron motif .…”

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confidence: 99%