- Single-Handed Helical Poly(quinoxaline-2,3-diyl)s Bearing Achiral 4-Aminopyrid-3-yl Pendants as Highly Enantioselective, Reusable Chiral Nucleophilic Organocatalysts in the Steglich Reaction
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Helically chiral poly(quinoxaline-2,3-diyl)s bearing 4-aminopyrid-3-yl pendants were synthesized as new helical-polymer-based chiral nucleophilic organocatalysts. The obtained chiral nucleophilic polymer catalysts exhibited high catalytic activity, enantioselectivity, and reusability in asymmetric Steglich rearrangement of oxazolyl carbonate to C-carboxyazlactone. The polyquinoxaline-based, helically chiral DMAP catalyst mediated intramolecular acyl transfer selectively, by contrast with known small-molecule-based chiral organocatalysts, which also mediate intermolecular acyl transfers.
- Yamamoto, Takeshi,Murakami, Ryo,Suginome, Michinori
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supporting information
p. 2557 - 2560
(2017/03/01)
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- Modulating NHC catalysis with fluorine
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Fluorination often confers a range of advantages in modulating the conformation and reactivity of small molecule organocatalysts. By strategically introducing fluorine substituents, as part of a β-fluoroamine motif, in a triazolium pre-catalyst, it was possible to modulate the behaviour of the corresponding N-heterocyclic carbene (NHC) with minimal steric alterations to the catalyst core. In this study, the effect of hydrogen to fluorine substitution was evaluated as part of a molecular editing study. X-ray crystallographic analyses of a number of derivatives are presented and the conformations are discussed. Upon deprotonation, the fluorinated triazolium salts generate catalytically active N-heterocyclic carbenes, which can then participate in the enantioselective Steglich rearrangement of oxazolyl carbonates to C-carboxyazlactones (e.r. up to 87.0:13.0).
- Rey, Yannick P.,Gilmour, Ryan
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p. 2812 - 2820
(2014/01/06)
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- Organic base effects in NHC promoted O- to C-carboxyl transfer; Chemoselectivity profiles, mechanistic studies and domino catalysis
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The O- to C-carboxyl transfer of oxazolyl carbonates promoted by triazolinylidenes, generated in situ with NEt3, shows a markedly different rate and chemoselectivity profile to the same reaction promoted by triazolinylidenes generated using KHM
- Campbell, Craig D.,Collett, Christopher J.,Thomson, Jennifer E.,Slawin, Alexandra M. Z.,Smith, Andrew D.
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scheme or table
p. 4205 - 4218
(2011/07/29)
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- Catalytic enantioselective Steglich rearrangements using chiral N-heterocyclic carbenes
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The evaluation of a range of enantiomerically pure NHCs, prepared in situ from imidazolinium or triazolium salt precatalysts, to promote the catalytic enantioselective Steglich rearrangement of oxazolyl carbonates to their C-carboxyazlactones, is reported. Modest levels of enantioselectivity (up to 66% ee) are observed using oxazolidinone derived NHCs.
- Campbell, Craig D.,Concellon, Carmen,Smith, Andrew D.
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scheme or table
p. 797 - 811
(2011/08/06)
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- Probing the efficiency of N-heterocyclic carbene promoted O- to C-carboxyl transfer of oxazolyl carbonates
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(Chemical Equation Presented) Screening of a range of azolium salts, bases and solvents for reactivity indicates that triazolinylidenes, generated in situ with KHMDS in THF, promote the Steglich rearrangement of oxazolyl carbonates with high catalytic efficiency (typical reaction time 5 min at 1.5 mol % NHC). This protocol shows wide substrate applicability, even allowing the efficient generation of vicinal quaternary centers. An improved experimental procedure is also described that allows a simplified one-pot reaction protocol to be employed with similarly high catalytic efficiency.
- Thomson, Jennifer E.,Campbell, Craig D.,Concellon, Carmen,Duguet, Nicolas,Rix, Kathryn,Slawin, Alexandra M. Z.,Smith, Andrew D.
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p. 2784 - 2791
(2008/09/20)
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- Efficient N-heterocyclic carbene-catalyzed O- to C-acyl transfer
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An N-heterocyclic carbene promotes the rearrangement of α-amino acid derived O-acyl carbonates to their corresponding C-acylated isomers, generating a C-C bond and a quaternary stereocenter with high efficiency, under mild reaction conditions and with low
- Thomson, Jennifer E.,Rix, Kathryn,Smith, Andrew D.
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p. 3785 - 3788
(2007/10/03)
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- Enantioselective TADMAP-catalyzed carboxyl migration reactions for the synthesis of stereogenic quaternary carbon
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The chiral, nucleophilic catalyst TADMAP [1, 3-(2,2,2-triphenyl-1- acetoxyethyl)-4-(dimethylamino)-pyridine] has been prepared from 3-lithio-4-(dimethylamino)pyridine (5) and triphenylacetaldehyde (3), followed by acylation and resolution. TADMAP catalyzes the carboxyl migration of oxazolyl, furanyl, and benzofuranyl enol carbonates with good to excellent levels of enantioselection. The oxazole reactions are especially efficient and are used to prepare chiral lactams (23) and lactones (30) containing a quaternary asymmetric carbon. TADMAP-catalyzed carboxyl migrations in the indole series are relatively slow and proceed with inconsistent enantioselectivity. Modeling studies (B3LYP/6-31G*) have been used in qualitative correlations of catalyst conformation, reactivity, and enantioselectivity.
- Shaw, Scott A.,Aleman, Pedro,Christy, Justin,Kampf, Jeff W.,Va, Porino,Vedejs, Edwin
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p. 925 - 934
(2007/10/03)
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