Indene formation upon borane-induced cyclization of arylallenes, 1,1-carboboration, and retro-hydroboration

Hasenbeck, Max; Wech, Felix; Averdunk, Arthur; Becker, Jonathan; Gellrich, Urs

doi:10.1039/d1cc01750k

Cited by 10 publications

(23 citation statements)

References 31 publications

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“…Prime examples are the 1,1-carboborations of alkynes and aryl allenes by tris(perfluoro)phenylborane (BCF). [3,4] Furthermore, the Piers' borane-induced catalytic trimerization of alkyl allenes and the dimerization of aryl allenes were reported by Erker and co-workers. [5] These reactions are initiated by the hydroboration of the allene.…”

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confidence: 94%

Piers′ Borane‐Induced Tetramerization of Arylacetylenes

Hasenbeck

Müller

Averdunk

et al. 2021

Chemistry A European J

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We herein report that the reaction of Piers' borane, i. e. HB(C 6 F 5 ) 2 , with an excess of arylacetylenes at room temperature leads to tetramerization of the acetylene and the diastereoselective formation of boryl-substituted tetra-aryltetrahydropentalenes. The reaction mechanism was investigated by isotope labeling experiments and DFT computations. These investigations indicate that a series of 1,2-[a

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confidence: 94%

Piers′ Borane‐Induced Tetramerization of Arylacetylenes

Hasenbeck

Müller

Averdunk

et al. 2021

Chemistry A European J

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“…Furthermore, this step dictates the regioselectivity of the carboboration. The central carbon of the allene binds to the borane so that in the zwitterion 5 the positive charge is resonance stabilized and in a benzylic and allylic position [2k,6b] . The computed barrier of 20.8 kcal mol −1 for the formation of the zwitterion 5 is in favourable agreement with the mild reaction conditions.…”

Section: Resultsmentioning

confidence: 58%

“…Thus, the computations agree with the experimentally observed chemoselectivity. We further considered the formation of an indene ring system by an intramolecular Friedel‐Crafts type reaction [2k,6b] . Again, the respective transition state TS indene is kinetically disfavoured by 7.1 kcal mol −1 (see inset Figure 2).…”

Section: Resultsmentioning

confidence: 99%

“…The groups of Hashmi and Stephan reported the cyclopropanation and the formation of allyl boranes by 1,1‐carboboration of enynes and propargylic esters, respectively [2e,j] . We recently reported that the reaction of phenylallene with BCF leads to the formation of a C 6 F 5 ‐substituted indene via a cyclisation, 1,1‐carboboration, retro‐hydroboration sequence [2k] . In contrast, there are still only a few reports on uncatalyzed 1,2‐carboborations [4] .…”

Section: Introductionmentioning

confidence: 99%

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1,2‐Carboboration of Arylallenes by In Situ Generated Alkenylboranes for the Synthesis of 1,4‐Dienes

Averdunk

Hasenbeck

Müller

et al. 2022

Chemistry A European J

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We herein report a novel method for the coupling of unactivated alkynes and arylallenes, which relies on an unprecedented and regioselective 1,2‐carboboration of the allene by an alkenylborane. The alkenylborane is conveniently prepared in situ by hydroboration of an alkyne with Piers’ borane, i. e., HB(C6F5)2. The boryl‐substituted 1,4‐dienes that are formed by this carboboration are well‐suited for a subsequent Suzuki‐Miyaura coupling with aryl iodides. This allowed us to develop a three‐step, one‐pot protocol for the synthesis of aryl‐substituted 1,4‐dienes. The generality of the reaction was demonstrated by the synthesis of twenty dienes with modular variations of all three reaction partners. The mechanism of the new 1,2‐carboboration was investigated using dispersion corrected double‐hybrid DFT computations that allowed us to rationalize the chemo‐ and regioselectivity of this key step.

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“…BCF yields pentafluorophenyl substituted indene 45 (Scheme 22). [20] As a side product of this reaction, allylborane 22 was observed, indicating that Piers' borane 6 is formed as an intermediate during the reaction.…”

Section: Discussionmentioning

confidence: 92%

Reactions of Allenes with strong Borane‐Based Lewis Acids

Gellrich

2021

Eur J Org Chem

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In recent years, reactions of unsaturated organic molecules with strong boron-based Lewis acids have attracted considerable attention. In this review, reactions of allenes with boron-based Lewis acids, especially such ones equipped with perfluorophenyl rings, are discussed. It is shown that depending on the substitution pattern of the allene and the borane, a surprisingly broad variety of chemical transformations can be observed.These transformations often include unexpected skeletal rearrangements of the former allene. Furthermore, some transformations require only catalytic amounts of the borane-based Lewis acid. Within this minireview, emphasis is given to the mechanistic aspects of these transformations, and similarities in the initial reaction steps are outlined.

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Indene formation upon borane-induced cyclization of arylallenes, 1,1-carboboration, and retro-hydroboration

Abstract: We herein report the reaction of arylallenes with tris(pentafluorophenyl)borane that yields pentafluorophenyl substituted indens. The tris(pentafluorophenyl)borane induces the cyclization of the allene and transfers a pentafluorophenyl ring in the course...

Cited by 10 publications

References 31 publications

Piers′ Borane‐Induced Tetramerization of Arylacetylenes

Piers′ Borane‐Induced Tetramerization of Arylacetylenes

1,2‐Carboboration of Arylallenes by In Situ Generated Alkenylboranes for the Synthesis of 1,4‐Dienes

Reactions of Allenes with strong Borane‐Based Lewis Acids

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