A Highly Chemoselective, Zr-Catalyzed C–O Bond Functionalization of Benzofuran

Yow, Shuhui; Nako, Adi E.; Neveu, Léonard; White, Andrew J. P.; Crimmin, Mark R.

doi:10.1021/om4008295

Cited by 19 publications

(13 citation statements)

References 49 publications

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“…1) were capable of the dearomatisation and ring-expansion of benzofuran using a zirconocene catalyst and t-butylethylene as a hydrogen-acceptor. 16 We later showed that the efficiency of this reaction could be improved using [Pd(PCy 3 ) 2 ] in the place of the zirconium catalyst. In both the non-catalysed and catalysed processes, the aluminium reagent (either 1 or 2) inserts selectively into one of the sp 2 C-O bonds of the 5-membered ring of benzofuran.…”

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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“…1 ). 5 , 6 In the case of fluorocarbons two competing pathways are observed: hydrodefluorination and C–F alumination. 5 …”

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confidence: 99%

“…From a mechanistic perspective, these data highlight the possibility that an in situ transition metal catalysed Al( iii ) → Al( i ) transformation may be operating in our previously reported bond functionalisation chemistry employing the Al( iii ) dihydride 1 . 5 , 6 From a more pragmatic point of view, the reactions result in the generation of a new carbon–aluminium bond from ‘inert’ carbon–fluorine or carbon–oxygen bonds. This approach represents a method for directly generating reactive intermediates from non-reactive chemical feedstocks, that uses the most abundant metal in the earth's crust without the need for expensive or toxic transition metal catalysts.…”

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confidence: 99%

Oxidative addition of carbon–fluorine and carbon–oxygen bonds to Al(i)

2015

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“…In 2013, we demonstrated that aluminium(III) hydride reagents (2) were capable of the dearomatisation and ring-expansion of benzofuran using a zirconocene catalyst and t-butylethylene as a hydrogen-acceptor. 16 We later showed that the efficiency of this reaction could be improved using [Pd(PCy 3 ) 2 ] in the place of the zirconium catalyst. In both the non-catalysed and catalysed processes, the aluminium reagent (either 1 or 2) inserts selectively into one of the sp 2 C-O bonds of the 5-membered ring of benzofuran.…”

Section: Introductionmentioning

confidence: 99%

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

Hooper¹,

Brown²,

Rekroukh³

et al. 2020

Preprint

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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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A Highly Chemoselective, Zr-Catalyzed C–O Bond Functionalization of Benzofuran

Cited by 19 publications

References 49 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

Oxidative addition of carbon–fluorine and carbon–oxygen bonds to Al(i)

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

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