Stereoselective radical addition of carbon-centred radicals to the dehydroalanine moiety of the chiral nickel(<scp>II</scp>) complex of the Schiff′s base derived from (S)-2-[N-(N′-benzylprolyl)amino]benzophenone and dehydroalanine

Gasanov, R. G.; Il'inskaya, L. V.; Misharin, Michail A.; Maleev, Victor I.; Raevski, Nicolai I.; Ikonnikov, N. S.; Orlova, S. A.; Кузьмина, Н. А.; Belokoń, Yuri N.

doi:10.1039/p19940003343

Cited by 26 publications

(23 citation statements)

References 17 publications

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“…While the pioneering works in this field were based on the use of harmful radical initiators such as Et 3 B, Bu 3 SnH, and AIBN, [86][87][88][89][90][91][92][93][94][95]97,[144][145][146][147] later the chemists found that the less toxic zinc, indium and copper are also capable as reductants to generate radicals from more hard reagents. [96,97,148,151,152,[162][163][164] In the past 5 years, a new round of development in the asymmetric synthesis of non-proteinogenic AAs has been begun by photoredox chemistry.…”

Section: Methodsmentioning

confidence: 99%

“…Non-proteinogenic (S)-β-benzoyl alanine 19 a was isolated by acidic hydrolysis of the Scheme 14. Asymmetric synthesis of the α-AAs 25 by addition of carbon-centred radicals generated by AIBN/Bu 3 SnH-system to a chiral Ni(II) complex 23 a (Belokon, 1994). [87] Scheme 15.…”

Section: Seebach-beckwith Alkene As a Chiral Substratementioning

confidence: 99%

“…Asymmetric synthesis of the α-AAs 25 by addition of carbon-centred radicals generated by AIBN/Bu 3 SnH-system to a chiral Ni(II) complex 23 a (Belokon, 1994). [87] Scheme 15. Asymmetric synthesis of the α-AA derivatives 26 by addition of radicals generated from olefins by iron catalysis to a chiral Ni(II) complex 23 a and the isolation of α-AA 27 b (Larionov, 2019).…”

Section: Seebach-beckwith Alkene As a Chiral Substratementioning

confidence: 99%

“…[117][118][119][120][121][122][123] In the subsequent work, the authors applied a chiral dehydroalanine Ni(II) complex (S)-23 a as an olefin type substrate for the conjugate addition of in situ generated radicals providing the β-substituted α-aminopropanoic acid derivatives (S,S)-24 (Scheme 14). [87] The addition of the alkyl radicals generated by AIBN and Bu 3 SnH to double bond in the ligand sphere of a Ni(II) complex (S)-23 a gave a mixture of diastereoisomeric complexes (S,S)-24 and (S,R)-24 with 40-90% diastereoselectivity in high yields (up to 90%) ( Scheme 14). As in the case of Beckwith, [86,88] the diastereoselectivity of the reaction depended on the size of the entering radicals, and the best asymmetric induction was achieved in case of tBu radical.…”

Section: Belokon's Chiral Nickel(ii) Complexes Of Dehydroalanine Schimentioning

confidence: 99%

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Advances in Asymmetric Amino Acid Synthesis Enabled by Radical Chemistry

2020

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Chiral amino acids (AAs), being the main "building" blocks of the living organisms, are also an important class of organic compounds which broadly applied in synthetic chemistry, biochemistry, catalysis and the designing of new drugs. According to the industrial-commodity market, chiral non-proteinogenic AAs containing various functional groups come to the fore. To date, radical cross-coupling reactions are becoming an option as an attractive powerful tool for AA syntheses. Owing to mild reaction conditions and high functional-group tolerance, radical chemistry represents an ideal strategy for the synthesis of challenging complex non-proteinogenic AAs. Moreover, the radical cross-coupling allows introducing AA residue into drug scaffolds and natural compounds. In the present review, we wish to summarize and discuss all the reported to date methods of the asymmetric synthesis of AAs using radical chemistry by presenting a comprehensive account of the literature in this field going back to 1990. We especially emphasize on a radical chemistry approach and, exclusively, on stereoselective synthesis of various α-, β-, γ-AAs and derivatives employing a different type of radical initiators starting from AIBN and organostannes and ending with powerful photoredox catalysis. Furthermore, the mechanism of the reported reactions will be discussed. Radicals Generated from AA Derivatives in Conjugate Additions 6.1. Radicals Generated from α-Substituted Glycine Derivatives in AA Synthesis 6.2. Modification of Chiral AA Side Chain by Radical Chemistry 7.

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Section: Methodsmentioning

confidence: 99%

Section: Seebach-beckwith Alkene As a Chiral Substratementioning

confidence: 99%

Section: Seebach-beckwith Alkene As a Chiral Substratementioning

confidence: 99%

Section: Belokon's Chiral Nickel(ii) Complexes Of Dehydroalanine Schimentioning

confidence: 99%

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Advances in Asymmetric Amino Acid Synthesis Enabled by Radical Chemistry

2020

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“…Belokon et al reported on the tin-mediated radical conjugate addition to dehydroalanine-nickel complexes, modified by a chiral proline-derived benzophenone imine auxiliary [62]. Especially with bulky alkyl radicals, very high diastereomeric excesses were observed, rationalized by an efficient Si-face shielding of the intermediate a-radical in the square-planar nickel complex (Figure 3.36).…”

Section: Radical Conjugate Additionmentioning

confidence: 99%

Radical‐Mediated Synthesis of α‐Amino Acids and Peptides

Deska¹

2010

Amino Acids, Peptides and Proteins in Organic Chemistry

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j115or through radical degradation of functional groups present in the amino acid or peptide building block. Hydrogen Atom Transfer ReactionsHydrogen transfer reactions offer certain advantages as they allow for the direct substitution of nonactivated hydrogens both in carbon-carbon and carbonheteroatom coupling reactions. Although amino acids, and in particular peptides, can exhibit a broad number of carbon-hydrogen bonds capable of undergoing homolytic cleavage, a high degree of regio-and chemoselectivity is often observed. In general, hydrogen atom transfer reactions show high selectivities to form the most stabilized radical, which is in most cases the captodative a-carbon-centered radical. Both with the amino function as the free base or as N-amido derivatives, the unpaired spin density of a-carbon-centered amino acid radicals is extensively delocalized as a combined resonance effect from the electron-withdrawing (capto) carboxy group and the electron-donating (dative) amino or amido group, respectively. In contrast, a-radical formation of protonated or quaternized amino acid derivatives is less favored due to the lack of dative resonance stabilization (Figure 3.2) [1].Easton et al. studied the radical formation behavior of different N-acyl amino acid methyl esters and their relative stabilities [2]. Contrary to the expectation that tertiary radicals are more stable than secondary ones, in the a-bromination reaction using Nbromosuccinimide, the reaction of the glycine derivative was faster than the bromination of corresponding alanine and valine derivatives. This phenomenon has been attributed to the destabilizing effects of nonbonding interactions in the different radical species. The stabilization of the captodative a-radical results from overlap of the semioccupied p-orbital with the p-orbitals of the amido and the methoxycarbonyl groups, which is maximal in a planar conformation. In comparison to the glycinyl radical, the alaninyl radical will thereby be destabilized due to the nonbonding interaction between the methyl side-chain and the amido oxygen; even stronger destabilizing effects result from nonbonding interactions with the sterically more demanding isopropyl group in the valinyl radical. By this means, N-methylation causes also destabilization, so that both alanine and sarcosine derivatives show comparable reaction rates; on the other, hand methyl pyroglutaminate, relatively free R Figure 3.

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Asymmetric Metal‐Templated Approach to Amino Acids with a CF₃‐Containing 3,2’‐Pyrrolidinyl Spirooxindole Core via a Michael/Mannich [3+2]‐Cycloaddition Reaction

Gugkaeva,

Stukalova,

Smol'yakov

et al. 2023

Adv Synth Catal

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We report here a practical protocol for the asymmetric synthesis of amino acids (AAs) with a CF3‐containing 3,2’‐pyrrolidinyl spirooxindole skeleton with three defined carbon stereocenters via a sequential Michael/Mannich [3+2]‐cycloaddition reaction. The coupling of a robust and stereochemically stable chiral dehydroalanine Ni(II) complex with various N‐2,2,2‐trifluoroethylisatin ketimines in the presence of triethylamine afforded a library of single diastereomeric complexes with a 3,2’‐pyrrolidinyl spirooxindole moiety in 36–71% yields. In particular, the change of base to LiOH allowed to obtain predominantly the Michael addition product in 76% yield. Finally, the decomposition of the obtained Ni(II) complexes with 3 N HCl provided the target complex AA with a 3,2’‐pyrrolidinyl spirooxindole core and (2S,4R)‐2,4‐diamino‐5,5,5‐trifluoropentanoic acid – an (S)‐norvaline derivative, together with easy recovery of the chiral auxiliary ligand for the synthesis of the starting dehydroalanine complex.

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Stereoselective radical addition of carbon-centred radicals to the dehydroalanine moiety of the chiral nickel(II) complex of the Schiff′s base derived from (S)-2-[N-(N′-benzylprolyl)amino]benzophenone and dehydroalanine

Cited by 26 publications

References 17 publications

Advances in Asymmetric Amino Acid Synthesis Enabled by Radical Chemistry

Advances in Asymmetric Amino Acid Synthesis Enabled by Radical Chemistry

Radical‐Mediated Synthesis of α‐Amino Acids and Peptides

Asymmetric Metal‐Templated Approach to Amino Acids with a CF₃‐Containing 3,2’‐Pyrrolidinyl Spirooxindole Core via a Michael/Mannich [3+2]‐Cycloaddition Reaction

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Stereoselective radical addition of carbon-centred radicals to the dehydroalanine moiety of the chiral nickel(II) complex of the Schiff′s base derived from (S)-2-[N-(N′-benzylprolyl)amino]benzophenone and dehydroalanine

Cited by 26 publications

References 17 publications

Advances in Asymmetric Amino Acid Synthesis Enabled by Radical Chemistry

Advances in Asymmetric Amino Acid Synthesis Enabled by Radical Chemistry

Radical‐Mediated Synthesis of α‐Amino Acids and Peptides

Asymmetric Metal‐Templated Approach to Amino Acids with a CF3‐Containing 3,2’‐Pyrrolidinyl Spirooxindole Core via a Michael/Mannich [3+2]‐Cycloaddition Reaction

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Product

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Asymmetric Metal‐Templated Approach to Amino Acids with a CF₃‐Containing 3,2’‐Pyrrolidinyl Spirooxindole Core via a Michael/Mannich [3+2]‐Cycloaddition Reaction