New solid-phase catalysts for asymmetric synthesis: cross-linked polymers containing a chiral Schiff base-zinc complex

Itsuno, Shinichi; Sakurai, Yoshiki; Ito, Koichi; Maruyama, Toshihiro; Nakahama, Seiichi; Fréchet, Jean M. J.

doi:10.1021/jo00288a051

Cited by 176 publications

(61 citation statements)

References 4 publications

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“…[30] Similarly, diethylzinc was immobilized on resins containing amino alcohol groups and were used in continuous-flow additions to aromatic aldehydes. [31] Thus, diethylzinc and p-chlorobenzaldehyde were added simultaneously with slow rate under nitrogen into an icecooled column containing the chiral polymer 11 a and 1-(pchlorophenyl)propanol was isolated in 94 % ee. The authors note that 58 mmol of the optically active alcohol were prepared in a continuous process by employing only 0.7 mmol of the polymer-attached catalyst.…”

Section: Applications Of Reactions and Multistep Syntheses In Flow-thmentioning

confidence: 99%

Continuous Flow Techniques in Organic Synthesis

Jas¹,

Kirschning²

2003

Chemistry A European J

457

220

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As part of the dramatic changes associated with the need for preparing compound libraries in pharmaceutical and agrochemical research laboratories, the search for new technologies that allow automation of synthetic processes has become one of the main topics. Despite this strong trend for automation high-throughput chemistry is still carried out in batches, whereas flow-through processes are rather restricted to production processes. This is far from understandable because the main advantages of that approach are facile automation, reproducibility, safety, and process reliability, because constant reaction parameters can be assured. Indeed, methods and technologies are missing that allow rapid transfer from the research level to process development without time-consuming adaptation and optimization of methods from the laboratory scale to production plant scale. Continuous-flow processes are considered as a universal lever to overcome these restrictions and, only recently, joint efforts between synthetic and polymer chemists and chemical engineers have resulted in the first continuous-flow devices and microreactors; these allow rapid preparation of compounds with minimum workup. Many of these approaches use immobilized reagents and catalysts, which are embedded in a structured flow-through reactor. It is generally accepted, that for achieving best reaction and kinetic parameters for convective-flow processes monolithic materials are ideally suited as solid phases or polymer supports. In addition, immobilization techniques have to be developed that allow facile regeneration of the active species in the reactor.

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Section: Applications Of Reactions and Multistep Syntheses In Flow-thmentioning

confidence: 99%

Continuous Flow Techniques in Organic Synthesis

Jas¹,

Kirschning²

2003

Chemistry A European J

457

220

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“…Gel-phase "C-NMR spectrum (in CDCI,) of the polymer thus obtained. For the cross-linking radical polymerization, we chose the suspension technique which is known to provide spherical particles of rather uniform sizes, and we followed procedures given in a monograph [19] and in a seminal article by FrPchet and coworkers [20] This produced quantitatively the polymers of Type I1 (3S37, 'no spacer'), of Type I11…”

Section: Scheme 2 Preparation Of a Taddol-modified Merrifield Resin mentioning

confidence: 99%

Polymer‐ and Dendrimer‐Bound Ti‐TADDOLates in Catalytic (and Stoichiometric) Enantioselective Reactions: Are pentacoordinate cationic Ti complexes the catalytically active species?

Seebàch¹,

Martí

Hintermann

1996

Helvetica Chimica Acta

230

143

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ct,rx,a',a'-Tetraaryl-l,3-dioxolane-4,5-dimethanols (TADDOLs), containing styryl groups either at C(2) of the heterocyclic ring or in the a-position, were prepared in the usual way (18-22,24,25). These compounds were copolymerized with styrene and divinylbenzene in a suspension, yielding polymers (3340, Scheme 3) as beads with a rather uniform particle-size distribution (1 5 M 5 0 pm), swellable in common organic solvents. HOCH,-and BrCH,-substituted TADDOLs were also prepared and used for attachement to Merrtfield resin or to dendritic molecules (23, 2632). The TADDOL moieties in these materials are accessible to form Ti (and Al) complexes (Scheme 4 ) which can be used as polymer-or dendrimer-bound reagents (stoichiometric) or Lewis acids (catalytic). The reactions studied with these new chiral auxiliaries are: enantioselective nucleophilic additions to aldehydes (of R,Zn and RTi(OCHMe,),; Scheme 5, Table I) and to ketones (of LiAIH,, Table 2); enantioselective ring opening of meso-anhydrides (Scheme 6); [4+2] and [3+2] cycloadditions of 3-crotonyl-1,3-oxazolidin-2-one to cyclopentadiene and to (Z)-N-benzylidenephenylamine N-oxide (4 48,49, Scheme 7, Tables 3, 4, and Fig. 5). The enantioselectivities reached with most of the polymer-bound or dendritic TADDOL Iigands were comparable or identical to those observed with the soluble analogs. The activity of the polymer-bound Lewis acids was only slightly reduced as compared with that encountered under homogeneous conditions. Multiple use of the beads (up to 10 times), without decreased performance, has been demonstrated (Figs. 3 and 4). The poorer selectivity in the Diels-Alder reaction (Scheme 7a), induced by the polymer-bound C1,Ti-TADDOLate as compared to the soluble one, is taken as an opportunity to discuss the mechanism of this Lewis-acid catalysis, and to propose a cationic, trigonal-bipyramidal complex as the catalytically active species (Fig. 6 ) . It is suggested that similar cations may be involved in other Ti-TADDOLate-mediated reactions as well.

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“…[4] Although very high enantioselectivities have been achieved in some instances, the primary goal of developing a reasonably fast process has remained elusive, and the reported catalysts and experimental set-ups involve very long residence times and multiple pass operation for the achievement of reasonable conversion levels. [5] In recent years, we have been engaged in the design of functional amino alcohols that could be immobilized onto organic or inorganic supports with minimal perturbation of the molecular regions where the catalytic activity resides. [6] As a fruit of this effort, we have been able to develop polymer-supported amino alcohol ligands 1-4 that control the enantioselective alkylation and arylation of aldehydes without any significant decrease in reaction rate or in enantioselectivity with respect to their homogeneous counterparts.…”

Section: Introductionmentioning

confidence: 99%

Fast and Enantioselective Production of 1‐Aryl‐1‐propanols through a Single Pass, Continuous Flow Process

2008

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A functional polymer 4, obtained by reaction of (R)-2-(1-piperazinyl)-1,1,2-triphenylethanol with a Merrifield resin, has been loaded in a packed bed reactor and used as catalyst for the continuous enantioselective production of 1-arylpropanols by ethylation of aromatic aldehydes. The high catalytic activity depicted by 4 allows the complete conversion of the substrates with the use of stoichiometric reagent ratios and unprecedently short residence times (down to 2.8 min). In practice, a single-pass operation can be used for all the studied aldehydes, and productions of up to 13.0 mol/g h are recorded. The sequential operation of the flow system for the uninterrupted synthesis of a small library of enantiopure 1-arylpropanols is also reported.

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New solid-phase catalysts for asymmetric synthesis: cross-linked polymers containing a chiral Schiff base-zinc complex

Cited by 176 publications

References 4 publications

Continuous Flow Techniques in Organic Synthesis

Continuous Flow Techniques in Organic Synthesis

Polymer‐ and Dendrimer‐Bound Ti‐TADDOLates in Catalytic (and Stoichiometric) Enantioselective Reactions: Are pentacoordinate cationic Ti complexes the catalytically active species?

Fast and Enantioselective Production of 1‐Aryl‐1‐propanols through a Single Pass, Continuous Flow Process

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