Copper‐Catalyzed Ring‐Opening Silylation of Benzofurans with Disilane

Saito, Hayate; Nogi, Keisuke; Yorimitsu, Hideki

doi:10.1002/anie.201806237

Cited by 28 publications

(12 citation statements)

References 44 publications

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“…These include, nickel catalysed ring-expansion borylation reported in 2016, 18,19 and copper catalysed ring-opening silylation reported in 2018. 20 Silyl lithium reagents react directly with benzofuran to effect the dearomatisation and ring-opening. 21 Despite these elegant advances, to date the reaction scope of the catalytic ringexpansion chemistry has not been extended to include furans, arguably a more important target due to their availability from biomass.…”

Section: Introductionmentioning

confidence: 99%

Catalyst control of selectivity in the C–O bond alumination of biomass derived furans

et al. 2020

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Section: Introductionmentioning

confidence: 99%

Catalyst control of selectivity in the C–O bond alumination of biomass derived furans

et al. 2020

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“…(3), Scheme ] . It is worth highlighting that the above examples represent the breakthroughs within this domain . However, the catalytic systems involving ring opening of benzofurans and subsequent elaboration are still limited.…”

Section: Methodsmentioning

confidence: 99%

Copper‐Catalyzed Ring Opening of Benzofurans and an Enantioselective Hydroamination Cascade

et al. 2018

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A copper(II) acetate/(R)‐DTBM‐SEGPHOS‐catalyzed ring opening of benzofurans and enantioselective hydroamination cascade with dimethoxymethylsilane (DMMS) and hydroxylamine esters is described. Starting from readily available substituted benzofurans, a series of chiral N,N‐dibenzylaminophenols, which are of high interest in pharmaceutical chemistry, were obtained with excellent enantioselectivities (up to 66 % yield, 94 % ee).

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“…These include, nickel catalysed ring-expansion borylation reported in 2016 18,19 and copper catalysed ring-opening silylation reported in 2018. 20 Silyl lithium reagents react directly with benzofuran to effect the dearomatisation and ring-opening. 21 Despite these elegant advances, to date the reaction scope of the catalytic ring-expansion chemistry has not been extended to include furans, arguably a more important target due to their availability from biomass rather than from coal.…”

Section: Figure 1 C-o Bond Alumination Of Furansmentioning

confidence: 99%

Catalyst Control of Selectivity in the C–O Bond Alumination of Biomass Derived Furans

Hooper¹,

Brown²,

Rekroukh³

et al. 2020

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Non-catalysed and catalysed reactions of aluminium reagents with furans, dihydrofurans and dihydropyrans were investigated and lead to the ring-expanded products due to the formal insertion of the aluminium reagent into a C–O bond of the heterocycle. Specifically, the reaction of [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl, 1) with furan, 2-methylfuran, 2,3-dimethylfuran and 2-methoxyfuran proceeded between 25 and 80 ºC leading to ring-expanded and dearomatised products due to the net transformation of a sp2 C–O bond into a sp2 C–Al bond. The kinetics of the reaction of 1 with furan were found to be 1st order with respect to 1 with activation parameters ΔH‡ = +19.7 (± 2.7) kcal mol-1, ΔS‡ = –18.8 (± 7.8) cal K-1 mol-1 and ΔG‡298 K = +25.3 (± 0.5) kcal mol-1 and a KIE of 1.0 ± 0.1. DFT calculations support a stepwise mechanism involving an initial (4+1) cycloaddition of 1 with furan to form a bicyclic intermediate that rearranges by an a-migration. The selectivity of ring-expansion is influenced by factors that weaken the sp2 C–O bond through population of the s*-orbital. Inclusion of [Pd(PCy3)2] as a catalyst in these reactions results in expansion of the substrate scope to include 2,3-dihydrofurans and 3,4-dihydropyrans but also improves the selectivity. Under catalysed conditions, the C–O bond that breaks is that adjacent to C–H bond. The aluminium(III) dihydride reagent [{(MesNCMe)2CH}AlH2] (Mes = 2,4,6-trimethylphenyl, 2) can also be used under catalytic conditions to effect a dehydrogenative ring-expansion of furans. Further mechanistic analysis of the Pd-catalysed reaction of 1 with furan shows that C–O bond functionalisation occurs via an initial C–H bond alumination. Kinetic products can be isolated that are derived from installation of the aluminium reagent at the 2-position of the heterocycle. C–H alumination proceeds with a strong primary KIE of 4.8 ± 0.3 consistent with a turnover limiting step involving oxidative addition of the C–H bond to a palladium catalyst. Isomerisation of the kinetic C–H aluminated product to the thermodynamic C–O ring expansion product is an intramolecular process that is again catalysed by [Pd(PCy3)2]. DFT calculations suggest that the key C–O bond breaking step involves attack of an aluminium based metalloligand on the 2-palladated heterocycle. The new methodology has been applied to the upgrading of molecules derived from furfuraldehyde, an important platform chemical from biomass.

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Copper‐Catalyzed Ring‐Opening Silylation of Benzofurans with Disilane

Cited by 28 publications

References 44 publications

Catalyst control of selectivity in the C–O bond alumination of biomass derived furans

Catalyst control of selectivity in the C–O bond alumination of biomass derived furans

Copper‐Catalyzed Ring Opening of Benzofurans and an Enantioselective Hydroamination Cascade

Catalyst Control of Selectivity in the C–O Bond Alumination of Biomass Derived Furans

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