Designer Lewis acid catalysts—bulky aluminium reagents for selective organic synthesis

Saitō, Susumu; Yamamoto, Hisashi

doi:10.1039/a607464b

Cited by 120 publications

(58 citation statements)

References 31 publications

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“…This activation would allow rapid in situ capture of an enolate intermediate generated on deprotonation. Aluminum tris(2,6-diphenylphenoxide) [ATPH] [17] was the reagent of choice, since it could effectively encapsulate a number of a,b-unsaturated carbonyl compounds. [18] Our initial effort concerned a basic system that has a single site for deprotonation: the reaction between crotonaldehyde and benzaldehyde, both of which were precomplexed with ATPH.…”

Section: Directed Mixed Aldol Condensation Between Twomentioning

confidence: 99%

Directed Aldol Condensation

Saitō

Yamamoto

1999

Chem. Eur. J.

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Crossed aldol condensation has traditionally been carried out by mixing two different carbonyl units under protic conditions with general acids or bases as the triggers of the reaction. [1] Development in this area has significantly expanded the scope of directed aldol condensation. Its synthetic potential has been particularly well-featured by those reactions that occurr in an intramolecular manner, such as Robinson annulation [2] and Dickemann condensation; [3] their analogous processes [4] have also been found quite attractive. Unfortunately, because of difficulties in directing the coupling intermolecularly, the conventional aldol condensatiton has serious disadvantages:1) It gives low selectivities including stereo-, regio-and chemoselectivity involved in both enolization and aldolization processes. 2) It cannot necessarily suppress dehydration; this leads to a,b-unsaturated carbonyl compounds that can undergo further side reactions, such as Michael addition with enolates, to contaminate the reaction. This sometimes leads to further oligomerization and/or polymerization.3) The method often suffers from proton transfer from a carbonyl compound to a reactive enolate; this results in multiple functionalization. As a consequence, a desirable cross-coupling is significantly retarded or completely suppressed.[a] Prof.

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Section: Directed Mixed Aldol Condensation Between Twomentioning

confidence: 99%

Directed Aldol Condensation

Saitō

Yamamoto

1999

Chem. Eur. J.

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“…4 For some time now aluminium alkoxides and phenoxides have been the focus of research attempts to develop initiators for the ring opening polymerisation (ROP) of cyclic esters, such as rac-lactide and e-caprolactone to form poly-lactide and poly-caprolactone respectively. 5- 16 These so-called single site catalysts rely on the utility of ligand systems that are capable of augmenting the electronic and coordinative characteristics of the active metal centre, such that control over molecular weight distribution and stereochemistry of the propagating polymer chain can be controlled.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and structure of aluminium amine-phenolate complexes

et al. 2009

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Reaction of Al(OiPr)3 with the tris-phenol amine ligand L1H3 in toluene at ambient temperature results in the formation of the iso-propanol adduct [HOiPr.Al(L1)]. Single crystal X-ray diffraction analysis reveals the structure to be a hydrogen bonded dimer. Reaction of Al(OiPr)3 (or AlMe3) with L1H3 in THF affords the related, and structurally characterised THF adduct, [THF.Al(L1)]. Similar reaction of Al(OiPr)3 (or AlMe3) with the bis-phenol amine and tetra-phenol diamine ligands, L2H3 and L3H4, results in the formation and isolation of the complexes [Al(L2)]2 and [Al(L3)H] respectively, both of which have been structurally characterised via single crystal X-ray diffraction studies. Reaction of the alkoxide bridged dimer [Al(L2)]2 with the strong Lewis base HMPA results in the formation of the monomeric HMPA adduct [HMPA.Al(L2)] which was also structurally characterised. The adduct [HOiPr.Al(L1)] and the dimer [Al(L2)]2 were tested for their activity in the ring-opening polymerisation (ROP) of rac-lactide under solvent-free conditions (130 degrees C). Under the conditions employed [Al(L2)]2 failed to produce polymer after 48 h, in stark contrast to [HOiPr.Al(L1)] which after 24 h and 48 h produced narrow molecular weight polymer (24 h: yield=25%, Mn=14500 and PDI=1.05; 48 h: yield=65%, Mn=47700 and PDI=1.06).

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“…As result, catalysts based on metal salts such as aluminium, titanium and tin halides are widely used in several synthetic methods [17]. Conversely, the use of catalysts based on metal complexes as such rare earth metal triflates and metallocene compounds has been also developed [18].…”

Section: Environmental Benefits Of Use Of Lewis Acid Catalysts For Bimentioning

confidence: 99%

Esterification of Oleic Acid for Biodiesel Production Catalyzed by SnCl2: A Kinetic Investigation

2008

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Abstract:The production of biodiesel from low-cost raw materials which generally contain high amounts of free fatty acids (FFAs) is a valuable alternative that would make their production costs more competitive than petroleum-derived fuel. Currently, the production of biodiesel from this kind of raw materials comprises a two-stage process, which requires an initial acid-catalyzed esterification of the FFA, followed by a basecatalyzed transesterification of the triglycerides. Commonly, the acid H 2 SO 4 is the catalyst on the first step of this process. It must be said, however, that major drawbacks such as substantial reactor corrosion and the great generation of wastes, including the salts formed due to neutralization of the mineral acid, are negative and virtually unsurmountable aspects of this protocol. In this paper, tin(II) chloride dihydrate (SnCl 2 ·2H 2 O), an inexpensive Lewis acid, was evaluated as catalyst on the ethanolysis of oleic acid, which is the major component of several fat and vegetable oils feedstocks. Tin chloride efficiently promoted the conversion of oleic acid into ethyl oleate in ethanol solution and in soybean oil samples, under mild reaction conditions. The SnCl 2 catalyst was shown to be as active as the mineral acid H 2 SO 4 . Its use has relevant advantages in comparison to mineral acids catalysts, such as less corrosion of the reactors and as well as avoiding the unnecessary neutralization of products. Herein, the effect of the principal parameters of reaction on the yield and rate of ethyl oleate production has been investigated. Kinetic measurements revealed that the esterification of oleic acid catalyzed by SnCl 2 ·2H 2 O is first-order in relation to both FFAs and catalyst concentration. Experimentally, it was verified that the energy of activation of the esterification reaction of oleic acid catalyzed by SnCl 2 was very close those reported for H 2 SO 4 . OPEN ACCESSEnergies 2008, 1 80

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Designer Lewis acid catalysts—bulky aluminium reagents for selective organic synthesis

Cited by 120 publications

References 31 publications

Directed Aldol Condensation

Directed Aldol Condensation

Synthesis and structure of aluminium amine-phenolate complexes

Esterification of Oleic Acid for Biodiesel Production Catalyzed by SnCl2: A Kinetic Investigation

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