Tetrabutylammonium Tribromide (TBATB) as An Efficient Generator of HBr for an Efficient Chemoselective Reagent for Acetalization of Carbonyl Compounds

Gopinath, Rangam; Haque, Sk Jiaul; Patel, Bhisma K.

doi:10.1021/jo025701o

Cited by 128 publications

(79 citation statements)

References 28 publications

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“…laldehydes 4 i and 4 j were obtained in good overall yields, by the reaction of the acetal-protected amine 5 [30] the with corresponding isocyanates, followed by the removal of the acetal protecting group. Then, the resulting urea-functionalized salicylaldehydes 4 a-k were condensed with (R,R)-1,2-diaminocyclohexane to afford the bis-urea salen ligands 6 ak.…”

Section: Resultsmentioning

confidence: 99%

Self‐Assembly Approach toward Chiral Bimetallic Catalysts: Bis‐Urea‐Functionalized (Salen)Cobalt Complexes for the Hydrolytic Kinetic Resolution of Epoxides

Park

Lang

Abboud

et al. 2011

Chemistry A European J

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A series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-urea hydrogen-bonding interactions. These bis-urea (salen)Co catalysts resulted in rate acceleration (up to 13 times) in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in THF by facilitating cooperative activation, compared to the monomeric catalyst. In addition, one of the bis-urea (salen)Co(III) catalyst efficiently resolves various terminal epoxides even under solvent-free conditions by requiring much shorter reaction time at low catalyst loading (0.03-0.05 mol %). A series of kinetic/mechanistic studies demonstrated that the self-association of two (salen)Co units through urea-urea hydrogen bonds was responsible for the observed rate acceleration. The self-assembly study with the bis-urea (salen)Co by FTIR spectroscopy and with the corresponding (salen)Ni complex by (1)H NMR spectroscopy showed that intermolecular hydrogen-bonding interactions exist between the bis-urea scaffolds in THF. This result demonstrates that self-assembly approach by using non-covalent interactions can be an alternative and useful strategy toward the efficient HKR catalysis.

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Section: Resultsmentioning

confidence: 99%

Self‐Assembly Approach toward Chiral Bimetallic Catalysts: Bis‐Urea‐Functionalized (Salen)Cobalt Complexes for the Hydrolytic Kinetic Resolution of Epoxides

Park

Lang

Abboud

et al. 2011

Chemistry A European J

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“…[38] We have been interested in the development of several green chemical processes in aqueous media [39] and in exploring the catalytic properties of tetrabutylammonium tribromide (TBATB) for various organic transformations. [40] In this regard, we have found that TBATB is a useful reagent whose acidity can be tuned from highly acidic to near neutral pH in the appropriate organic solvent. This reagent has been proved to be a good catalyst for the chemoselective acetalization of carbonyl compounds, [40a] pyranylation/depyranylation of alcohols [40b] and thioacetalization and transthioacetalization of carbonyl compounds.…”

Section: Resultsmentioning

confidence: 99%

Reinvestigation of the Mechanism of gem‐Diacylation: Chemoselective Conversion of Aldehydes to Various gem‐Diacylates and Their Cleavage under Acidic and Basic Conditions

Kavala

Patel

2005

Eur J Org Chem

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The mechanism of gem-diacylate formation has been studied extensively using tetrabutylammonium tribromide (TBATB) as the catalyst. The reaction proceeds by a nucleophilic attack of an anhydride on an aldehydic carbonyl group, nucleophilic attack of the hemiacylate intermediate on a second molecule of the anhydride, followed by an intermolecular attack of a second acetate group to regenerate the anhydride. gem-Diacylates of various aliphatic and aromatic aldehydes were obtained directly from the reaction of a variety of aliphatic and aromatic acid anhydrides in the presence of a catalytic quantity of tetrabutylammonium tribromide (TBATB) under solvent-free conditions. A significant electronic effect was observed during its formation as well as deprotection to the corresponding aldehyde. Chemoselective gem-diacylation of the aromatic aldehyde containing an electrondonating group has been achieved in the presence of an aldehyde containing an electron-withdrawing group. Depro-

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“…Cyclohexanone diethyl acetal was identified by comparison of their NMR spectra and GC profiles with those of the authentic sample, prepared according to a literature method. [14] Amphiphiles 1-3 and corresponding composites 1-MS-3-MS were prepared by using methods analogous to those reported previously. [7] Measurements: Electronic absorption spectra were recorded on a JASCO U-best V-570 spectrophotometer.…”

Section: Methodsmentioning

confidence: 99%

Catalysis of a Peptidic Micellar Assembly Covalently Immobilized within Mesoporous Silica Channels: Importance of Amphiphilic Spatial Design

Otani

Kinbara

Zhang

et al. 2007

Chemistry A European J

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A mesostructured silica/organic composite 1-MS, constructed from a rodlike micelle of amino acid amphiphile 1 that has a condensable head group and that can be used as a template, was found to be able to catalyze the acetalization of cyclohexanone, in ethanol at 25 degrees C (50% in 12 h), whereas no reaction took place with unfunctionalized mesoporous silica. In sharp contrast, hydrolytic removal of the C16 alkyl tail of immobilized 1 resulted in the complete disappearance of the catalytic activity, which suggests the importance of a hydrophobic inner domain for the admission of cyclohexanone. Unsupported peptide amphiphile 2, under identical conditions to those above, was inefficient for acetalization regardless of the absence (2% in 24 h) or presence of mesoporous silica (7% in 24 h). Reference composite 2-MS, which is a noncovalently immobilized peptidic micelle, was virtually inactive (1% in 24 h). These observations indicate the importance of covalent immobilization of the peptidic rod micelle for catalysis. Mesostructured silicate 3-MS hybridized with a nonpeptidic, ammonium ion amphiphile (3) showed a certain catalytic activity, but the yield (12% in 24 h) of the acetal was much lower than that achieved by using 1-MS as the catalyst. Amorphous silica with immobilized 1 on its surface was much less active than 1-MS for acetalization (5% in 24 h).

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Tetrabutylammonium Tribromide (TBATB) as An Efficient Generator of HBr for an Efficient Chemoselective Reagent for Acetalization of Carbonyl Compounds

Cited by 128 publications

References 28 publications

Self‐Assembly Approach toward Chiral Bimetallic Catalysts: Bis‐Urea‐Functionalized (Salen)Cobalt Complexes for the Hydrolytic Kinetic Resolution of Epoxides

Self‐Assembly Approach toward Chiral Bimetallic Catalysts: Bis‐Urea‐Functionalized (Salen)Cobalt Complexes for the Hydrolytic Kinetic Resolution of Epoxides

Reinvestigation of the Mechanism of gem‐Diacylation: Chemoselective Conversion of Aldehydes to Various gem‐Diacylates and Their Cleavage under Acidic and Basic Conditions

Catalysis of a Peptidic Micellar Assembly Covalently Immobilized within Mesoporous Silica Channels: Importance of Amphiphilic Spatial Design

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