Recent advances in organocatalytic atroposelective reactions

• Henrich Szabados and
• Radovan Šebesta

Beilstein J. Org. Chem. 2025, 21, 55–121, doi:10.3762/bjoc.21.6

• been prepared, which aims to provide an update on the last five years of this burgeoning area with some relevant links to key earlier works. The material in this article is divided according to the major activation mode of the organocatalyst, from covalent activation via enamine and iminium activation

• advances in organocatalytic atroposelective syntheses. Review Atroposelective reactions via enamine and iminium activation Iminium activation was utilized in the synthesis of axially chiral styrenes. Tan and co-workers developed an atroposelective strategy toward axially chiral alkenylarenes 3 based on an

• organocatalytic Michael addition to alkynals 2 (Scheme 1) [18]. The authors identified the Jørgensen–Hayashi-type catalyst C1 as the most efficient organocatalyst. In this way, a range of axially chiral styrenes were obtained in high yields and enantiomeric purities. The reaction was based on an iminium

Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts

• Mandeep K. Chahal

Beilstein J. Org. Chem. 2024, 20, 3085–3112, doi:10.3762/bjoc.20.257

• catalysis of Diels–Alder reaction in aqueous environment catalyzed by TPPS3 53 supramolecular aggregates [67]. The Diels–Alder reaction between cinnamaldehyde (55) and cyclopentadiene (56) proceeds via iminium activation by the zwitterionic hetero-aggregates derived from TPPS3 molecules 53 and a cyclic

Stereoselective mechanochemical synthesis of thiomalonate Michael adducts via iminium catalysis by chiral primary amines

• Michał Błauciak,
• Dominika Andrzejczyk,
• Błażej Dziuk and
• Rafał Kowalczyk

Beilstein J. Org. Chem. 2024, 20, 2313–2322, doi:10.3762/bjoc.20.198

• significant advancement in mechanocatalysis. The stereoselective addition of bisthiomalonates 1–4 to cyclic enones and 4-chlorobenzylideneacetone proceeds stereoselectively under iminium activation conditions secured by chiral primary amines, in contrast to oxo-esters as observed in dibenzyl malonate addition

• product with 93% ee after 24 h, while the bifunctional primary amine-thiourea catalysts (system B) required 4 days to provide an adduct with similar enantioselectivity. Prolonged reaction time is in general the innate nature of organocatalytic reactions employing iminium activation approaches. With the

New advances in asymmetric organocatalysis

• Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 240–242, doi:10.3762/bjoc.18.28

• within the area. Organocatalytic reactions are highly suitable components of cascade transformations as exemplified by the seminal work of Enders [13]. Besides traditional enamine and iminium activation of carbonyl compounds other activation modes were uncovered which significantly broadened the

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• effect of the iminium activation. The Diels–Alder reaction of alkyne 1a with 2,3-dimethylbutadiene also occurred under very mild conditions and yielded the iminium-substituted 1,4-cyclohexadiene 4-Ch (Scheme 2), which, due to its high sensitivity toward moisture, was not purified but was further

Investigations towards the stereoselective organocatalyzed Michael addition of dimethyl malonate to a racemic nitroalkene: possible route to the 4-methylpregabalin core structure

• Denisa Vargová,
• Rastislav Baran and
• Radovan Šebesta

Beilstein J. Org. Chem. 2018, 14, 553–559, doi:10.3762/bjoc.14.42

• . Stereoselective Michael addition, one of the most important organocatalytic reactions [8] usually serves as a key stereoinduction transformation. Earlier studies, performed by Hayashi and Wang employed iminium activation to perform the enantioselective addition of nitromethane to enals for syntheses of baclofen

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

• Chittaranjan Bhanja,
• Satyaban Jena,
• Sabita Nayak and
• Seetaram Mohapatra

Beilstein J. Org. Chem. 2012, 8, 1668–1694, doi:10.3762/bjoc.8.191

• to 56%) and enantioselectivities in the range of 85–91% ee (Scheme 9). Mechanistically the reaction involves the iminium activation of the α,β-unsaturated cyclic enones by the chiral pyrrolidine catalyst. Very recently, Xu and co-workers [51] reported an improved protocol for the same reaction

• salicylaldehydes 1 and nitroalkenes 27 employing (S)-1-methyl-2-(pyrrolidin-2-ylmethylthio)-1H-imidazole (VIII) as organocatalyst in the presence of salicylic acid as cocatalyst and in DMSO as solvent (Scheme 14). The reaction was interpreted as following an aromatic iminium activation strategy and provided 2H

• -mercaptobenzaldehydes 36 and α,β-unsaturated cyclic ketones 38 proceeded in a highly chemoselective fashion, furnishing the corresponding products 39 in high yield and with moderate to good ee. The mechanism proposed involves the same iminium activation (Scheme 18) of the α,β-unsaturated cyclic ketones by the chiral

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• -imidazoline relative to 2-benzylidene-imidazolidine is explained by the gain of aromaticity during electrophilic additions to the imidazoline derivatives. O-Methylated Breslow intermediates are a hundred-fold less nucleophilic than deoxy Breslow intermediates. Keywords: enamine activation; iminium activation