Benzimidazole Nitrogen-Directed, Regiocontrolled, Lithiation of Ferrocenyl- and Phenyl-<i>N</i>-<i>n</i>-butylbenzimidazoles

Hérault, Damien; Aelvoet, Karel; Blatch, Alexandrea J.; Al‐Majid, Abdullah Mohammed; Smethurst, Christian A.; Whiting, Andrew

doi:10.1021/jo061639+

Cited by 21 publications

(31 citation statements)

References 34 publications

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“…Compound 1 was synthesized according to Scheme . The key starting material, ( N -methylbenzimidazol-2-yl)ferrocene ( 1a ), was obtained by a procedure modified from that used for a related compound reported previously . The benzimidazolyl-directed ortho lithiation of 1a , followed by addition of 1 equiv of dimesitylboron fluoride, led to the formation of compound 1 , which was isolated in ∼60% yield as a reddish crystalline solid.…”

Section: Resultsmentioning

confidence: 99%

Reactivity and Electronic Properties of a Ferrocene Molecule Bearing an N,C-Chelated BMes₂ Unit

et al. 2014

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A dimesitylboron-functionalized benzimidazolylferrocene, B(2-ferrocenyl-N-Me-benzimidazolyl)Mes 2 (1), has been synthesized and fully characterized. The B−N bond in 1 was found to undergo a dynamic dissociation/association process in solution, leading to a dynamic exchange of the two mesityls bound to the boron atom and slow hydrolysis of 1 under ambient conditions. The hydrolyzed product 2-BMes(OH)-1-(N-methylbenzimidazol-2-yl)ferrocene (2) was isolated and characterized, in which the boron center has a trigonal-planar geometry with one of the mesityls being replaced by an OH − group. The photoisomerization process of the boron unit in 1 was fully inhibited by the low lying d−d/MLCT states of the ferrocene unit. Compound 1 can be oxidized readily by I 2 , forming the ferrocenium species [1 + ]I 3 -(3). NMR and EPR data for 3 indicated a notable spin delocalization through space from the Fe(III) center to a flanking mesityl group.

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Section: Resultsmentioning

confidence: 99%

Reactivity and Electronic Properties of a Ferrocene Molecule Bearing an N,C-Chelated BMes₂ Unit

et al. 2014

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“…Significantly, 2 b can be isolated as an analytically pure ate complex (see the http://www.wiley-vch.de/contents/jc_2002/2008/z704293_s.pdf) showing a single 11 B NMR chemical shift at δ =0.3 ppm. Alternatively, 2 b can be generated in situ in water from the corresponding boroxine ( δ =19.7 ppm)7e by the addition of three equivalents of sodium hydroxide, which gives an identical 11 B NMR spectrum with no signal corresponding to uncomplexed boronic acid ( δ =32.8 ppm) 7e. The in situ generation of 2 b can be directly used to produce identical catalytic effects.…”

Section: Product Ratios and Yields For The Aldol Reactions Outlined Imentioning

confidence: 99%

A Catalytic Aldol Reaction and Condensation through In Situ Boron “Ate” Complex Enolate Generation in Water

et al. 2008

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Cooperation is key: N‐Butyl‐1‐benzimidazole‐2‐phenylboronic acid hydroxide complex catalyzes the aldol condensation and aldol addition between hydroxyacetone or acetone, and different aldehydes in water. The catalytic activity results from cooperative interactions between the boronate complex and the imidazole function. Aldol condensation gives the unsaturated methyl ketones of acetone, whereas aldol addition predominates with hydroxyacetone.

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“…We recently reported using a (−)‐sparteine‐directed metallation to provide 2 in 96 % ee 9. Attempts to prepare other planar chiral aminoboronic acids such as 3 were hindered by the lack of direct access by asymmetric deprotonation methods of ferrocene benzimidazole precursors 8d. However, this was circumvented by the synthesis of 3 from the known10 ( pS )‐bromoferrocene aldehyde 4 (Scheme ).…”

Section: Methodsmentioning

confidence: 99%

Asymmetric Direct Amide Synthesis by Kinetic Amine Resolution: A Chiral Bifunctional Aminoboronic Acid Catalyzed Reaction between a Racemic Amine and an Achiral Carboxylic Acid

et al. 2008

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The formation of amide bonds by direct reaction of amines with carboxylic acids by thermal [1, 2] or catalytic methods [2][3][4][5] is generally a high temperature process. There have been no reports to date of any reactions that involve asymmetric induction during direct amide formation, with the exception of an enzyme-catalyzed process.[6] Lower temperatures are often preferred for any reaction as it can reduce the amount of reagent, reactant, or thermal product degradation. A more important consideration is that asymmetric induction processes are usually more efficient at lower temperatures because small differences in energy between diasteroisomeric transition states are amplified; however, there are an increasing number of examples where this is not the case and improved asymmetric induction can be obtained at higher temperatures. [7] With these considerations in mind, we endeavored to develop a catalytic direct amide formation under mild conditions, though still well above room temperature. The current limiting temperature appears to be 85 8C, the temperature at which reactions can be carried out with bifunctional aminoboronic acid catalysts by using azeotropic water removal in fluorobenzene.[2] Although these reaction conditions are relatively mild compared to all other direct amide formation reactions with boron-derived catalyts, [4,5] they do not completely preclude the thermal direct amide formation with the more reactive carboxylic acid/amine combinations.[2] Though the prospect of developing asymmetric catalysts for amide formation may not look promising, [7] we report herein preliminary results that demonstrate asymmetric processes are possible under elevated temperatures with the development of a planar chiral ferrocenederived bifunctional aminoboronic acid catalyst.Our recent interests in the development of bifunctional aminoboronic acids as potential catalysts [8] led to the development of N,N-di-iso-propylbenzylaminoboronic acid type catalysts [2] such as commercially available 1 and planar chiral ferrocene analogue 2. We recently reported using a (À)-sparteine-directed metallation to provide 2 in 96 % ee.[9]Attempts to prepare other planar chiral aminoboronic acids such as 3 were hindered by the lack of direct access by asymmetric deprotonation methods of ferrocene benzimidazole precursors.[8d] However, this was circumvented by the synthesis of 3 from the known [10] (pS)-bromoferrocene aldehyde 4 (Scheme 1).Coupling aldehyde 4 with diamine 5[8c] in the presence of Oxone gave bromoferrocenylbenzimidazole 6 in 89 % yield and 99 % ee (determined by chiral HPLC methods, see the Supplementary Information), which compares with a literature value of 98 % ee for aldehyde 4.[10] Subsequent lithiumhalogen exchange of 6 provided enantioenriched catalyst 3 (60 % yield).A series of parallel experiments were conducted with catalysts 2 and 3, in which carboxylic acids 7 a-b were reacted with amines 8 a-c in refluxing fluorobenzene by using activated 3-molecular sieves in a Soxhlet (solvent drying system). Th...

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Benzimidazole Nitrogen-Directed, Regiocontrolled, Lithiation of Ferrocenyl- and Phenyl-N-n-butylbenzimidazoles

Cited by 21 publications

References 34 publications

Reactivity and Electronic Properties of a Ferrocene Molecule Bearing an N,C-Chelated BMes₂ Unit

Reactivity and Electronic Properties of a Ferrocene Molecule Bearing an N,C-Chelated BMes₂ Unit

A Catalytic Aldol Reaction and Condensation through In Situ Boron “Ate” Complex Enolate Generation in Water

Asymmetric Direct Amide Synthesis by Kinetic Amine Resolution: A Chiral Bifunctional Aminoboronic Acid Catalyzed Reaction between a Racemic Amine and an Achiral Carboxylic Acid

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Benzimidazole Nitrogen-Directed, Regiocontrolled, Lithiation of Ferrocenyl- and Phenyl-N-n-butylbenzimidazoles

Cited by 21 publications

References 34 publications

Reactivity and Electronic Properties of a Ferrocene Molecule Bearing an N,C-Chelated BMes2 Unit

Reactivity and Electronic Properties of a Ferrocene Molecule Bearing an N,C-Chelated BMes2 Unit

A Catalytic Aldol Reaction and Condensation through In Situ Boron “Ate” Complex Enolate Generation in Water

Asymmetric Direct Amide Synthesis by Kinetic Amine Resolution: A Chiral Bifunctional Aminoboronic Acid Catalyzed Reaction between a Racemic Amine and an Achiral Carboxylic Acid

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Reactivity and Electronic Properties of a Ferrocene Molecule Bearing an N,C-Chelated BMes₂ Unit

Reactivity and Electronic Properties of a Ferrocene Molecule Bearing an N,C-Chelated BMes₂ Unit