A general protocol for the asymmetric synthesis of unnatural α-amino acids with γ-tertiary and quaternary carbon centers via generated radicals is reported.
Hydrogen bond donors (HBD) are a sustainable privileged class of catalysts which are broadly used for the activation of compounds in synthetic chemistry. Among them, the metal-templated HBD complexes present...
The selective addition of electrophilic C=C double bonds to the N–H bond of indoles is a challenging task due to the high nucleophilicity of indoles at their C3‐position. Herein, we report the successful selective intermolecular N‐functionalization of various indoles via aza‐Michael addition of C=C double bond of a dehydroalanine Schiff base, which takes place in the ligand sphere of a chiral NiII complex in the presence of sodium hydride. The resulting hydroaminated NiII complexes were isolated in 55–82 % yields with excellent diastereoselectivity (dr > 99:1) (8 examples). And the actual products of interest, namely (S)‐2‐amino‐3‐(1H‐indol‐1‐yl)propanoic acids, were subsequently released from the NiII complexes via aqueous HCl treatment of the NiII complexes and isolated with excellent enantioselectivity (> 99 % ee). The chiral auxiliary [(S)‐BPB = (S)‐2‐(N‐benzylprolyl)aminobenzophenone] and NiII ions can be easily recovered after the acidic complex cleavage step and reused for the synthesis of the starting NiII complex. Moreover, the indole′s preference for nucleophilic attack via its N1‐ over its C3‐position was rationalized by DFT calculations.
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.
A general protocol for the asymmetric synthesis of artificial amino acids (AAs) comprising an isoquinolone skeletal was successfully elaborated via a straightforward Rh(III)-catalyzed C−H activation/annulation of various aryl hydroxamates with...
A family of well-defined Λ-
and Δ-configured
octahedral
cationic chiral-at-cobalt catalysts were expanded through a straightforward
postcomplexation of the bromine-functionalized Co(III) complexes based
on (R,R)-1,2-cyclohexanediamine
and (S,S)-1,2-diphenylethylenediamine
by Suzuki–Miyaura cross-coupling reaction (CCR) with arylboronic
acids. The corresponding modified Co(III) complexes were isolated
by standard silica column chromatography with up to 65% yields. Indeed,
it is the first example of the direct modification of the ligand sphere
of chiral Co(III) catalysts through Suzuki–Miyaura CCR. It
was observed for the first time that the chiral metal center is epimerized
during the cross-coupling process at the transmetalation stage on
palladium catalyst in the case of minor diastereomers of Co(III) complexes
(Δ(R,R)-1 and
Λ(S,S)-2). Next,
the efficacies of obtained chiral metal-templated complexes 1–4 were evaluated in benchmark asymmetric
reactions in order to compare their catalytic activity. Chiral Co(III)
complexes 1–4 have been examined
as hydrogen bond donor (HBD) catalysts in such important reactions
as epoxidation of chalcone and the fixation of CO2 into
valuable cyclic carbonates.
Here we report the first synthesis
of two diastereomeric cationic
octahedral Co(III) complexes based on commercially available (R,R)-1,2-diphenylethylenediamine and salicylaldehyde.
Both diastereoisomers with opposite chiralities at the metal center
(Λ and Δ configurations) were prepared. The new Co(III)
complexes possessed both acidic hydrogen-bond donating (HBD) NH moieties
and nucleophilic counteranions and operate as bifunctional chiral
catalysts for the challenging kinetic resolution of terminal and disubstituted
epoxides by the reaction with CO2 under mild conditions.
The highest selectivity factor (s) of 2.8 for the trans-chalcone epoxide was achieved at low catalyst loading
(2 mol %) in chlorobenzene, which is the best achieved result currently
for this type of substrate.
Correction for ‘An asymmetric metal-templated route to amino acids with an isoquinolone core via a Rh(iii)-catalyzed coupling of aryl hydroxamates with chiral propargylglycine Ni(ii) complexes’ by Mikhail A. Arsenov et al., Org. Biomol. Chem., 2022, 20, 9385–9391, https://doi.org/10.1039/D2OB01970A.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.