Non-covalent organocatalyzed enantioselective cyclization reactions of α,β-unsaturated imines

• Sergio Torres-Oya and
• Mercedes Zurro

Beilstein J. Org. Chem. 2024, 20, 3221–3255, doi:10.3762/bjoc.20.268

• materials [1][2]. Due to their importance, different synthetic routes involving stoichiometric and catalytic approaches have been developed. The α,β-unsaturated imines, also known as conjugated imines or 1-azadienes, are useful precursors for the construction of aza-heterocycles. Due to their structure

• reported, providing a novel methodology for the construction of α,β-unsaturated imines [4]. There are different types of α,β-unsaturated imines, such as the acyclic imines aldimines, ketimines, or dienimines, depending on whether they are derived from aldehydes, ketones, or doubly unsaturated ketones

• , respectively. Additionally, the most common cyclic α,β-unsaturated imines involve benzofuran or saccharin-derived azadienes (Figure 1). Cycloaddition reactions, especially Diels–Alder reactions, have attracted a lot of attention since their discovery as one of the most powerful methodologies for the

Asymmetric organocatalytic synthesis of chiral homoallylic amines

• Nikolay S. Kondratyev and
• Andrei V. Malkov

Beilstein J. Org. Chem. 2024, 20, 2349–2377, doi:10.3762/bjoc.20.201

• ,β-unsaturated imines 9. However, with ethynylimines 12, the enantioselectivity dropped to a modest level. In addition, the reaction with sterically hindered tertiary allylboronates, such as the chiral (R)-α-cyclohexyl-α-methyl-allylboronate required the use of catalytic amounts of zinc tert-butoxide

• 11. It was proposed, that the internal hydrogen bond between the catalyst 11 and the P=O fragment of the protecting group of imine 9 is responsible for the observed high enantioselectivities (76–98% ee). The scope included a wide range of substrates, such as aromatic, heteroaromatic, aliphatic, and α

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• β-borylation of α,β-unsaturated imines 416 was reported using CuCl/L/NaO-t-Bu (L = PCy3, Ph3P, JosiPhos) which, upon oxidation with NaBO3, delivered the desired β-imino alcohol 418 (Scheme 67). It is postulated that the base is responsible for the displacement of chloride from the catalyst and also

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• substituents in the Cα-position facilitate a base induced rearrangement to α,β-unsaturated imines, while azide-substituted propargylamines form triazoles under surprisingly mild conditions. A panel of propargylamines bearing fluoro or chloro substituents, polar functional groups, or basic and acidic functional

• groups is accessible for the use as precursors of peptidomimetics. Keywords: amino acid analogous side chains; desilylation; Ellman’s chiral sulfinamide; intramolecular Huisgen reaction; peptidomimetics; propargylamines; rearrangement to α,β-unsaturated imines; Introduction Terminal alkynes display an

• structure analysis. Due to the extended π-system of the α,β-unsaturated imines 12i and 12k, the progress of the propargylamide–allenylamide rearrangement that eventually leads to the formation of the α,β-unsaturated imines by tautomerism could be easily monitored by UV–vis spectroscopy. The reaction mixture

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• lower enantioselectivities for the addition of para-substituted anilines to α,β-unsaturated imines [41]. Gil and Collin have also reported on the same reaction as Sodeoka, but using a samarium-BINOL catalyst system, which proceeded with lower enantioselectivity [42]. Sodeoka found that minimizing the

Copper-mediated synthesis of N-alkenyl-α,β-unsaturated nitrones and their conversion to tri- and tetrasubstituted pyridines

• Dimitra Kontokosta,
• Daniel S. Mueller,
• Dong-Liang Mo,
• Wiktoria H. Pace,
• Rachel A. Simpson and
• Laura L. Anderson

Beilstein J. Org. Chem. 2015, 11, 2097–2104, doi:10.3762/bjoc.11.226

• ][38], fragment couplings [39][40][41][42], and transition metal-catalyzed C–H bond functionalization of α,β-unsaturated imines and oximes [43][44][45][46][47][48][49][50]. We were inspired by the copper-catalyzed coupling of protected α,β-unsaturated oximes and alkenylboronic acids developed by

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

• Rob De Vreese and
• Matthias D’hooghe

Beilstein J. Org. Chem. 2012, 8, 398–402, doi:10.3762/bjoc.8.43

• necessity of α,β-unsaturated imines as reaction partners has neither been evaluated nor discussed, and N-(arylmethylidene)amines and N-(alkylidene)amines should be evaluated as alternative imine substrates. Finally, further study of preliminary results regarding the use of achiral carbenes in combination

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• propargylic benzoates with α,β-unsaturated imines to give azepine products 35 with excellent yields [77]. The formal (4 + 3) cycloaddition takes place in three basic stages: 1) Generation of the gold carbenoid by a 1,2-acyloxy migration, 2) attack of the imine on these electrophilic species to give an allyl

• transformation is somewhat related to those previously described by Doyle and by Barluenga that involved α,β-unsaturated imines and rhodium–vinyl carbenoids (Doyle) or Fischer carbenes (Barluenga). However, the stereochemical outcome of these three processes is different [78][79]. Therefore, the reactivity of

• 1,3-dipolar cycloaddition of 2-(1-alkynyl)-2-alken-1-ones with α,β-unsaturated imines [49]. Gold-catalyzed (4 + 3) cycloadditions of 1-(1-alkynyl)oxiranyl ketones [50]. (3 + 2) Cycloaddition of gold-containing azomethine ylides [52]. Gold-catalyzed generation and reaction of azomethine ylides [53

Allylsilanes in the synthesis of three to seven membered rings: the silylcuprate strategy

• Asunción Barbero,
• Francisco J. Pulido and
• M. Carmen Sañudo

Beilstein J. Org. Chem. 2007, 3, No. 16, doi:10.1186/1860-5397-3-16

• ). Similarly, silylcupration of imines [25] provides a simple and efficient route for the preparation of seven membered carbocycles with different substitution patterns. Thus, reaction of 2 with α,β-unsaturated imines, at low temperature, affords allylsilane-containing aldehydes 47, which upon addition of

• formation from silylcupration of α,β-unsaturated imines. Seven membered ring formation from functionalized allylsilanes. Acknowledgements This paper is dedicated to Professor Miguel Yus Astiz on occasion of his 60th birthday. We thank the MEC of Spain (CTQ/2006-02436/BQU) and the JCyL (VA050-04) for