Toggling enantioselective catalysis—a promising paradigm in the development of more efficient and versatile enantioselective synthetic methodologies

Zanoni, Giuseppe; Castronovo, Francesca; Franzini, Maurizio; Vidari, Giovanni; Giannini, Elios

doi:10.1039/b201455f

Cited by 163 publications

(56 citation statements)

References 34 publications

(36 reference statements)

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“…Similar effects have been reported in other papers and are known as 'dual stereocontrol'. 10,11 Furthermore, in the case of the indane-fused oxazolines 6aA and 14, increasing the steric bulk of the tether resulted in a lower enantioselectivity. In contrast, when the chiral substituent on the oxazoline moiety was a t-butyl-substituent, higher enantioselectivities were obtained with a bulky phenyl-substituted tether.…”

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confidence: 99%

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Efficient one-step synthesis of chiral bidentate oxazoline-alcohol ligands via a cyclic imidate ester rearrangement

Noël

Robeyns

Meervelt

et al. 2009

Tetrahedron: Asymmetry

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Section: Contents Lists Available At Sciencedirectmentioning

confidence: 99%

“…5a This effect, together with the dual stereocontrol, suggests that the introduction of the phenyl substituents modifies the catalytic mechanism or the structure of the catalytic site. 10,11 3. Conclusion…”

Section: Contents Lists Available At Sciencedirectmentioning

confidence: 99%

Efficient one-step synthesis of chiral bidentate oxazoline-alcohol ligands via a cyclic imidate ester rearrangement

Noël

Robeyns

Meervelt

et al. 2009

Tetrahedron: Asymmetry

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“…[6] Many of the generally used chiral ligands are naturally available in only one enantiomer; the other enantiomer often requires a labor-intensive preparation. The importance of enantioselective catalysis has increased in this regard, as it allows easy access to both enantiomers of a product without any complex modification of the structure of the chiral promoter.…”

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confidence: 99%

“…[4] The successful application of these ligand systems motivated us to screen the Nozaki-Hiyama allylation of aromatic aldehydes. Initial evaluation of symmetrical (4)(5)(6) and non-symmetrical bipyridine ligands (1)(2)(3) in the Cr(II)-catalyzed addition of allyl halides to benzaldehyde revealed that C 2 -symmetrical Configuration [4a] To increase the applicability of the ligand system, the enantiomer 4a of ligand 4 was synthesized from (À)-b-pinene according to the synthetic protocol for ligand 4 ( Figure 1). An X-ray crystallographic analysis of (+)-6 ( Figure 2) verified the general structure of these tetradentate N 2 O 2 ligands, [5] which have features that resemble those of the well known Jacobsen salen ligand and TADDOL.…”

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C₂‐Symmetrical Bipyridyldiols as Promising Enantioselective Catalysts in Nozaki–Hiyama Allylation

et al. 2011

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Several new chiral bipyridyldiol ligands that promote the chromium-catalyzed enantioselective addition of allylic halides to aldehydes in up to 99% ee were synthesized. The chromium-catalyzed allylation of aldehydes using ligands 4 and 4a in the presence of chromiumA C H T U N G T R E N N U N G (III) chloride and allyl chloride provided the highest enantioselectivity.Keywords: asymmetric catalysis; bipyridyldiol; chromium catalysis; enantioselectivity; NozakiHiyama allylationThe nucleophilic addition of organochromium reagents [Nozaki-Hiyama-Kishi (NHK) reaction] to carbonyl compounds is a versatile carbon-carbon bond forming reaction that can be used with a wide range of substrates and has a diverse range of application.[1] The synthetic utility of the reaction has been significantly increased by the development of a catalytic redox process that involves the recycling of Cr(II) by the reduction of CrA C H T U N G T R E N N U N G (III) species.[2] These preliminary improvements have motivated numerous efforts to develop an enantioselective version of this reaction. Many structurally different chiral ligands were applied as enantioselective catalysts for the allylation of aldehydes, and have resulted in various degrees of asymmetric induction.[3] Notably, chiral salen, quinoline and oxazoline-based chromium complexes exhibit high enantioselectivities in the asymmetric allylation of aromatic and aliphatic aldehydes. In most of the catalyst systems, the use of less reactive allylic chlorides gave lower yields, while the more reactive allylic iodides worsened the stereochemical outcome of the reaction. To solve these problems, a new catalyst of the Nozaki-Hiyama allylation is desirable. This work is the first to describe a new C 2 -symmetrical bipyridyldiol-based chromium catalyst that is effective in the enantioselective addition of allyl chloride to aldehydes.Our recent study involved chiral bipyridine ligands from enantioenriched pinene which gave good enantioselectivities in several asymmetric transformations.[4] The successful application of these ligand systems motivated us to screen the Nozaki-Hiyama allylation of aromatic aldehydes. Initial evaluation of symmetrical (4-6) and non-symmetrical bipyridine ligands (1-3) in the Cr(II)-catalyzed addition of allyl halides to benzaldehyde revealed that C 2 -symmetrical Configuration

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“…We surveyed tert-butyl carbamate, tert-butyl carbazate, and aniline (Table 3); in all cases, the opposite enantiomer of the allylic amine analogue was produced as the major product relative to the hydroazidation reaction. Enantiodivergence in synthetic protocols has previously been reported, [23] and is usually brought about by modification of various reaction parameters, including catalyst identity (e.g. changes to metal or ligand), temperature, solvent, and additives, among others.…”

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Enantioselective, Stereodivergent Hydroazidation and Hydroamination of Allenes Catalyzed by Acyclic Diaminocarbene (ADC) Gold(I) Complexes

et al. 2016

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The gold-catalyzed enantioselective hydroazidation and hydroamination reactions of allenes are presented herein. ADC gold(I) catalysts derived from BINAM were critical for achieving high levels of enantioselectivity in both transformations. The sense of enantioinduction is reversed for the two different nucleophiles, allowing access to both enantiomers of the corresponding allylic amines using the same catalyst enantiomer. Graphical AbstractChiral allylic azides and amines may be obtained by enantioselective hydroazidation and hydroamination of allenes catalyzed by acyclic diaminocarbene gold(I) catalysts derived from BINAM. The sense of enantioinduction is reversed for the two different nucleophiles, allowing easy access to both enantiomers with a single catalyst enantiomer. Keywordshydroazidation; hydroamination; enantioselective; gold catalysis; acyclic diaminocarbene Allylic amines are an important functional motif in synthetic organic chemistry and they have been utilized in the synthesis of numerous biologically active compounds. [1] Closely related allylic azides are valuable precursors for allylic amines, as well as for amino acids [2] Correspondence to: F. Dean Toste, fdtoste@berkeley.edu. HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript and amine-containing natural products. [3] Allylic azides have typically been prepared via substitution reactions from the corresponding allylic halides, (homo)allylic alcohols, and their derivatives. [4] More recently, Pd-catalyzed C-H activation, [5] and Au-catalyzed hydroazidation of allenes [6] have been employed.While reports of the synthesis of allylic azides are numerous, methods for asymmetric azidation are few. [7] Fewer still are enantioselective hydroazidation reactions, which have only been reported in a formal sense via conjugate addition to activated double bonds (Scheme 1). [8][9][10] In light of recent examples of transition-metal catalysed asymmetric additions of nitrogen nucleophiles to allenes [11] and the growing utility of organic azides, we sought to develop a gold(I)-catalyzed enantioselective hydroazidation of allenes. Cognizant of potential regioselectivity issues from the Winstein rearrangement [12] of the product allylic azides, we initiated our studies using aryl allene 3a. [13] Initial studies revealed that the use of ethereal solvents was critical to obtaining reproducible data. [14] With the choice of solvent established, the enantioinduction afforded by a number of chiral gold(I) catalysts was evaluated under conditions similar to those previously reported, with trifluoroacetic acid (TFA) and trimethylsilyl azide (TMSN 3 ) used for in situ generation of hydrazoic acid (Table 2). [6] Traditional chiral phosphine gold(I) catalysts failed to afford high levels of enantioinduction (entries 1,2) as did a previously reported [15] phosphoramidite catalyst (entry 3). Chiral NHC gold(I) catalysts [16] (entries 4-6) also were found to be unsatisfactory. However, the use of a BINAM-derived ADC gold...

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Toggling enantioselective catalysis—a promising paradigm in the development of more efficient and versatile enantioselective synthetic methodologies

Cited by 163 publications

References 34 publications

Efficient one-step synthesis of chiral bidentate oxazoline-alcohol ligands via a cyclic imidate ester rearrangement

Efficient one-step synthesis of chiral bidentate oxazoline-alcohol ligands via a cyclic imidate ester rearrangement

C₂‐Symmetrical Bipyridyldiols as Promising Enantioselective Catalysts in Nozaki–Hiyama Allylation

Enantioselective, Stereodivergent Hydroazidation and Hydroamination of Allenes Catalyzed by Acyclic Diaminocarbene (ADC) Gold(I) Complexes

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Toggling enantioselective catalysis—a promising paradigm in the development of more efficient and versatile enantioselective synthetic methodologies

Cited by 163 publications

References 34 publications

Efficient one-step synthesis of chiral bidentate oxazoline-alcohol ligands via a cyclic imidate ester rearrangement

Efficient one-step synthesis of chiral bidentate oxazoline-alcohol ligands via a cyclic imidate ester rearrangement

C2‐Symmetrical Bipyridyldiols as Promising Enantioselective Catalysts in Nozaki–Hiyama Allylation

Enantioselective, Stereodivergent Hydroazidation and Hydroamination of Allenes Catalyzed by Acyclic Diaminocarbene (ADC) Gold(I) Complexes

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C₂‐Symmetrical Bipyridyldiols as Promising Enantioselective Catalysts in Nozaki–Hiyama Allylation