1H-Imidazol-4(5H)-ones and thiazol-4(5H)-ones as emerging pronucleophiles in asymmetric catalysis

Asymmetric catalysis represents a very powerful tool for the synthesis of enantiopure compounds. In this context the main focus has been directed not only to the search for new efficient chiral catalysts, but also to the development of efficient pronucleophiles. This review highlights the utility and first examples of 1H-imidazol-4(5H)-ones and thiazol-4(5H)-ones as pronucleophiles in catalytic asymmetric reactions.The authors acknowledge the University of the Basque Country UPV/EHU (UFI 11/22), the Basque Government (Grant No IT-628-13) and the Ministerio de Economia y Competitividad (MEC, Grant CTQ2013-47925-C2-1-P), Spain for financial support

syn-Selective Michael reaction of α-branched aryl acetaldehydes with nitroolefins promoted by squaric amino acid derived bifunctional Brønsted bases

[EN] Here we describe a direct access to 2,2,3-trisubstituted syn γ-nitroaldehydes by addition of α-branched aryl acetaldehydes to nitroolefins promoted by a cinchona based squaric acid-derived amino acid peptide. Different α-methyl arylacetaldehydes react with β-aromatic and β-alkyl nitroolefins to afford the Michael adducts in high enantioselectivity and syn-selectivity. NMR experiments and DFT calculations predict the reaction to occur through the intermediacy of E-enolate. The interaction between the substrates and the catalyst follows Pápai’s model, wherein an intramolecular H-bond interaction in the catalyst between the NH group of one of the tert-leucines and the squaramide oxygen seems to be key for discrimination of the corresponding reaction transition states.Support has been provided by the University of the Basque Country UPV/EHU (UFI QOSYC 11/22), Basque Government (GV grant IT1236-19), and Ministerio de Ciencia e Innovación (grant PID2019-109633GB-C21), Spain. A. G. and T. E. thank Basque Government and MINECO respectively for fellowships. We would like to express our gratitude to the students I. Gonzalez-Mujika and M. Campo for their participation in conducting some experiments of the reaction scope. We also thank SGIker (UPV/EHU) for providing NMR, HRMS. X-Ray and computational resources

Development of an α′-hydroxy enone for the aminocatalytic asymmetric formal conjugate addition of aldehydes to acrylates, vinyl ketones and acrolein

Aminocatalytic asymmetric conjugate addition of aldehydes to Michael acceptors is a well established C-C bond forming methodology. However, various acrylic-type acceptors, including acrylic acid derivatives and acrolein, remain reluctant. Here we demonstrate that the internal H-bonding self-activation in α'-hydroxy enones allows them to react smoothly with enolizable aldehydes using commercially available aminocatalysts to afford adducts in good yields and high enantioselectivity. Straightforward conversion of the ketol moiety of these adducts into aldehyde, ketone and carboxylic acid functionalities offers an indirect, unified entry to products derived from acrolein, alkyl-vinyl ketones and acrylates, respectively.Support has been provided by the Basque Government (GV grant IT‐1583‐22), and Ministerio de Ciencia e Innovación (grant PID2019‐109633GB/AEI/10.13039/501100011033), Spain. A predoctoral grant to B. L. from Navarra Government is acknowledged

Catalytic Asymmetric α-Functionalization of α-Branched Aldehydes

Aldehydes constitute a main class of organic compounds widely applied in synthesis. As such, catalyst-controlled enantioselective α-functionalization of aldehydes has attracted great interest over the years. In this context, α-branched aldehydes are especially challenging substrates because of reactivity and selectivity issues. Firstly, the transient trisubstituted enamines and enolates resulting upon treatment with an aminocatalyst or a base, respectively, would exhibit attenuated reactivity; secondly, mixtures of E- and Z-configured enamines/enolates may be formed; and third, effective face-discrimination on such trisubstituted sp2 carbon intermediates by the incoming electrophilic reagent is not trivial. Despite these issues, in the last 15 years, several catalytic approaches for the α-functionalization of prostereogenic α-branched aldehydes that proceed in useful yields and diastereo- and enantioselectivity have been uncovered. Developments include both organocatalytic and metal-catalyzed approaches as well as dual catalysis strategies for forging new carbon–carbon and carbon–heteroatom (C-O, N, S, F, Cl, Br, …) bond formation at Cα of the starting aldehyde. In this review, some key early contributions to the field are presented, but focus is on the most recent methods, mainly covering the literature from year 2014 onward.This research was funded by Basque Government (grant IT-1583-22) and by MCIN/AEI/10.13039/501100011033 (grant PID2019-109633GB-C21)

N-(Diazoacetyl)oxazolidin-2-thiones as Sulfur Donor Reagents: Asymmetric Synthesis of Thiiranes from Aldehydes

Financial support was provided by the University of the Basque Country UPV/EHU (UFI 11/22), Basque Government (GV grant No IT-291-07), and Ministerio de Ciencia e Innovación (MICINN, Grant CTQ2007-68095-C02), Spain. A. L. thanks MICINN and European Social Foundation for a Ramón y Cajal contract. I. O. thanks MCINN for a fellowship. We also thank SGIker (UPV/EHU) for providing NMR, HRMS, X-Ray, and computational resources

Synthesis of β-Hydroxy α-Amino Acids Through Brønsted Base-Catalyzed syn-Selective Direct Aldol Reaction of Schiff Bases of Glycine o-Nitroanilide

Here we report the highly enantio- and syn-selective synthesis of β-hydroxy α-amino acids from glycine imine derivatives under Brønsted base (BB) catalysis. The key of this approach is the use of benzophenone-derived imine of glycine o-nitroanilide as a pronucleophile, where the o-nitroanilide framework provides an efficient hydrogen-bonding platform that accounts for nucleophile reactivity and diastereoselectivity.Support has been provided by the University of the Basque Country UPV/EHU (UFI QOSYC 11/22), Basque Government (GV grant IT1236-19), and Ministerio de Ciencia e Innovación (MICINN, CTQ2016-78487-C2), Spain. A.V. thanks Basque Government, and I.U. and S.d.P. thank UPV/EHU. We also thank SGIker (UPV/EHU) for providing NMR, HRMS, X-ray, and computational resources

Asymmetric propionate aldol reactions of a chiral lithium enolate accessible from direct enolization with n-butyllithium

The presented lithium enolate-based methodology is suitable for access to propionate syn-aldol motifs with high levels of stereocontrol. The reactive lithium enolate species is generated by direct treatment of a camphor-based chiral ethyl ketone with butyllithium, and is subsequently submitted to aldolization with a broad variety of aldehydes. The product aldols are obtained in uniformly high yields and high d.r. values (ranging from 91:9 to >98:2) irrespective of the aliphatic (both linear and branched chain), α,β-unsaturated, aromatic, or hetero-aromatic nature of the aldehyde employed. The crystallinity of most of the obtained adducts offers an easy access to almost 100% isomerically pure products upon a single recrystallisation. The auxiliary (1R)- (+)-camphor can be removed easily from the adducts for reuse, thereby producing the corresponding syn propionate aldols. This technology is implemented in the synthesis of a key subunit of the multi-drug resistance reversing agent hapalosin.This work was finantially supported by the Universidad del País Vasco, Gobierno Vasco, and by MEC. Grants to M. C. G.-R. from Gobierno Vasco and to P. B. from MEC are acknowledged

Organocatalytic Michael Addition of Unactivated α-Branched Nitroalkanes to Afford Optically Active Tertiary Nitrocompounds

The direct, asymmetric conjugate addition of unactivated α-branched nitroalkanes is developed based on the combined use of chiral amine/ureidoaminal bifunctional catalysts and a tunable acrylate template to provide tertiary nitrocompounds in 55–80% isolated yields and high enantioselectivity (e.r. up to 96:4). Elaboration of the ketol moiety in thus obtained adducts allows a fast entry to not only carboxylic and aldehyde derivatives but also nitrile compounds and enantioenriched 5,5-disubstituted γ-lactams.We thank the Basque Government (EJ, grant IT1583-22) and Agencia Estatal de Investigación (grants PID2019-109633GB and PID2022-137153NB-C21/AEI/10.13039/501100011033) for financial support. A.G.-U. thanks EJ; B.L. thanks the Navarra Government, and M.E.-V. thanks UPNA (PJUPNA18-2022). Authors also thank SGIker (UPV/EHU/ERDF, EU) for providing NMR, HRMS, and X-ray resources