Diisobutylaluminum hydride-promoted cyclization of  o -(trimethylsilylethynyl)styrenes to substituted naphthalenes

Kinoshita, Hidenori; Yaguchi, Kazuki; Tohjima, Takayuki; Hirai, Nobuyoshi; Miura, Katsukiyo

doi:10.1016/j.tetlet.2016.03.099

Cited by 11 publications

(3 citation statements)

References 42 publications

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“…The classical arsenal is basically limited to dissolving metal reductions; other reagents capable of transferring electrons to triple bonds such as Cr(+2) have occasionally been used for the same purpose . Moreover, LiAlH 4 or related metal hydrides allow propargyl alcohols (and very few other substrates) to be converted to the corresponding E -configured allylic alcohols. − The use of alkali metals in liquid ammonia or of highly reactive aluminum hydrides, however, drastically limits the scope of these methods because applications to compounds containing other reducible and/or base-sensitive functionality are precluded.…”

Section: Introductionsupporting

confidence: 72%

Half-Sandwich Ruthenium Carbene Complexes Linktrans-Hydrogenation andgem-Hydrogenation of Internal Alkynes

et al. 2018

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The hydrogenation of internal alkynes with [Cp*Ru]-based catalysts is distinguished by an unorthodox stereochemical course in that E-alkenes are formed by trans-delivery of the two H atoms of H. A combined experimental and computational study now provides a comprehensive mechanistic picture: a metallacyclopropene (η-vinyl complex) is primarily formed, which either evolves into the E-alkene via a concerted process or reacts to give a half-sandwich ruthenium carbene; in this case, one of the C atoms of the starting alkyne is converted into a methylene group. This transformation represents a formal gem-hydrogenation of a π-bond, which has hardly any precedent. The barriers for trans-hydrogenation and gem-hydrogenation are similar: whereas DFT predicts a preference for trans-hydrogenation, CCSD(T) finds gem-hydrogenation slightly more facile. The carbene, once formed, will bind a second H molecule and evolve to the desired E-alkene, a positional alkene isomer or the corresponding alkane; this associative pathway explains why double bond isomerization and over-reduction compete with trans-hydrogenation. The computed scenario concurs with para-hydrogen-induced polarization transfer (PHIP) NMR data, which confirm direct trans-delivery of H, the formation of carbene intermediates by gem-hydrogenation, and their evolution into product and side products alike. Propargylic -OR (R = H, Me) groups exert a strong directing and stabilizing effect, such that several carbene intermediates could be isolated and characterized by X-ray diffraction. The gathered information spurred significant preparative advances: specifically, highly selective trans-hydrogenations of propargylic alcohols are reported, which are compatible with many other reducible functional groups. Moreover, the ability to generate metal carbenes by gem-hydrogenation paved the way for noncanonical hydrogenative cyclopropanations, ring expansions, and cycloadditions.

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Section: Introductionsupporting

confidence: 72%

Half-Sandwich Ruthenium Carbene Complexes Linktrans-Hydrogenation andgem-Hydrogenation of Internal Alkynes

et al. 2018

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“…Although dissolving metal reductions using (earth) alkali metals in liquid ammonia or amines are usually highly E -selective, they show a very narrow functional group compatibility and therefore hardly ever qualify for advanced applications . The same is true for the use of metal hydrides such as LiAlH 4 or Red-Al, which, above all, work only for propargylic alcohols and few other types of substrates. − Alternative procedures that have been applied to more than a handful of examples are basically missing …”

Section: Introductionmentioning

confidence: 99%

trans-Hydrogenation,gem-Hydrogenation, andtrans-Hydrometalation of Alkynes: An Interim Report on an Unorthodox Reactivity Paradigm

2018

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cis-Delivery of H2 to the π-system of an unsaturated substrate is the canonical course of metal catalyzed hydrogenation reactions. The semireduction of internal alkynes with the aid of [Cp*Ru]-based catalysts violates this rule and affords E-alkenes by direct trans-hydrogenation. A pathway involving σ-complexes and metallacyclopropenes accounts for this unconventional outcome. Connected to this process is an even more striking reactivity mode, in which both H atoms of H2 are delivered to one and the same C atom. Such gem-hydrogenation of stable carbogenic compunds is a fundamentally new transformation that leads to the formation of discrete metal carbene complexes. Computational studies suggest that the trans- and the gem-pathway have similar barriers, but polar substituents in the vicinity of the reacting triple bond provide opportunities for imposing selectivity and control. Moreover, it is shown that catalytic trans-hydrogenation is by no means a singularity: rather, the underlying principle is also manifest in trans-hydroboration, trans-hydrosilylation, trans-hydrogermylation, and trans-hydrostannation, which are equally paradigm-changing processes. These reactions are robust and distinguished by excellent compatibility with many (reducible) functional groups and have already stood the test of natural product synthesis in a number of demanding cases.

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“…82 83 At higher temperature, the related enyne 128 underwent skeletal rearrangement to form 1,2-dihydronaphthalen-1-ylaluminum reagent 131 via a cyclopropylcarbinylaluminum species 130 (Scheme 31b ). 84 Subsequent dehydroalumination formed the naphthalene 132 .…”

Section: Uncatalyzed Carboalumination Of Alkenesmentioning

confidence: 99%

Uncatalyzed Carbometallation Involving Group 13 Elements: Carboboration and Carboalumination of Alkenes and Alkynes

Woerpel¹,

Liu²

2022

Synthesis

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Carbometallations of alkenes and alkynes are powerful carbon–carbon bond-forming reactions. The use of compounds containing bonds between carbon and group 13 elements, particularly boron and aluminum, are particularly attractive because of the versatility of subsequent transformations. Uncatalyzed carboboration and carboalumination represent less common classes of reactions. This Short Review discusses uncatalyzed carboboration and carboalumination reactions of alkenes and alkynes, including the reaction design and mechanisms.1 Introduction2 Uncatalyzed Carboboration of Alkenes3 Uncatalyzed Carboboration of Alkynes4 Uncatalyzed Carboalumination of Alkenes5 Uncatalyzed Carboalumination of Alkynes6 Conclusion

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Diisobutylaluminum hydride-promoted cyclization of o -(trimethylsilylethynyl)styrenes to substituted naphthalenes

Cited by 11 publications

References 42 publications

Half-Sandwich Ruthenium Carbene Complexes Linktrans-Hydrogenation andgem-Hydrogenation of Internal Alkynes

Half-Sandwich Ruthenium Carbene Complexes Linktrans-Hydrogenation andgem-Hydrogenation of Internal Alkynes

trans-Hydrogenation,gem-Hydrogenation, andtrans-Hydrometalation of Alkynes: An Interim Report on an Unorthodox Reactivity Paradigm

Uncatalyzed Carbometallation Involving Group 13 Elements: Carboboration and Carboalumination of Alkenes and Alkynes

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