Florian Fischer

Abstract

Synthesis
DOI: 10.1055/s-0036-1591767

Diastereoselective Diels–Alder reactions of 2,6-diaryl-1,2-dihydropyridines with N-methylmaleimide afford highly substituted isoquinuclidines in good chemical yield (30–50%). This sequential one-pot synthesis is performed under microwave irradiation and involves, primarily, the synthesis of 2,6-diaryl-1,2-dihydropyridines by a 6π-azaelectrocyclisation involving an intermediate α,β,γ,δ-di-unsaturated imine, obtained by condensation of (E,E)-cinnamylideneacetophenones with amines. This procedure easily converts unstable 2,6-diaryl-1,2-dihydropyridines into, otherwise inaccessible, isoquinuclidines without any kind of manipulation.
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© Georg Thieme Verlag Stuttgart · New York

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Class of 86: A type of negatively curved nanographene with an unprecedented pattern of heptagons in a polycyclic framework of 86 sp² carbon atoms was successfully synthesized with ring expansion as a key step. The saddle-shaped π-backbone was revealed by X-ray crystallography, and its stereochemical dynamics were studied by DFT calculations. (Picture: substituents in crystal structure removed for clarity.)

[Communication]
Sai Ho Pun, Chi Kit Chan, Jiye Luo, Zhifeng Liu, Qian Miao
Angew. Chem. Int. Ed., January 10, 2018, https://doi.org/10.1002/anie.201711437 Read article

Dr. Andrew Ballard, Dr. Hiwa O. Ahmad, Dr. Stefania Narduolo, Lucy Rosa, Nikki Chand, Dr. David A. Cosgrove, Dr. Peter Varkonyi, Dr. Nabil Asaad, Dr. Simone Tomasi, Dr. Niklaas J. Buurma and Dr. Andrew G. Leach

The racemization potential of complex organic molecules has been predicted using simple quantum mechanical calculations and a group additivity scheme. Organic chemists can first check whether a given synthetic targets will be configurationally stable before embarking on a potentially lengthy and expensive chiral synthesis.

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Synthesis
DOI: 10.1055/s-0036-1591514

Several new trans-dihydronarciclasine analogues were stereo­selectively synthesised by applying our feasible and efficient process developed recently. These new phenanthridone alkaloid derivatives were obtained in both racemic and optically active forms. During their enantioselective syntheses, high selectivities (up to 99% ee) were achieved by using (8S,9S)-9-amino(9-deoxy)epiquinine as an organocatalyst. The modifications, the introduction of ethoxy or methoxy groups, were made in ring A of the phenanthridone scaffold.
[...]

© Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
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Synthesis
DOI: 10.1055/s-0036-1590955

An iron(III)-BPsalan complex was found to efficiently catalyze the asymmetric chlorination reaction of cyclic β-keto esters and N-Boc oxindoles, affording the corresponding chlorinated products in high yield and up to 92% ee with NCS as chlorination reagent under mild reaction conditions.
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© Georg Thieme Verlag Stuttgart · New York

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Formally achieved: Enantioenriched α-alkylated aldehydes (2) are synthesized by exploiting the ability of chiral enamines (A) to generate radicals from (phenylsulfonyl)alkyl iodides (1) and trap them in a stereoselective fashion. Coupling this step with the simple desulfonylation of 2 provides a method to install either a methyl or a benzyl moiety with high stereoselectivity. SET=single-electron transfer.

[Communication]
Giacomo Filippini, Mattia Silvi, Paolo Melchiorre
Angew. Chem. Int. Ed., March 21, 2017, https://doi.org/10.1002/anie.201612045 Read article

Nature Chemistry. doi:10.1038/nchem.2748

Authors: Mattia Silvi, Charlie Verrier, Yannick P. Rey, Luca Buzzetti & Paolo Melchiorre

Chiral iminium ions generated from an amine catalyst and enals are key organocatalytic intermediates in thermal asymmetric processes. Now, visible-light excitation of these iminium ions can turn these compounds into strong oxidants to enable enantioselective photochemical β-alkylations of enals with silanes, which are unachievable via conventional ground state pathways.

Publication date: 16 November 2016
Source:Tetrahedron Letters, Volume 57, Issue 46
Author(s): Mayara de Souza Siqueira, Luiz Carlos da Silva-Filho
Multicomponent reactions between β-ketoesters and benzaldehydes for the synthesis of 4H-pyran derivatives promoted by niobium pentachloride (NbCl5) were carried out, providing good yields and reasonable reaction times under mild reaction conditions.

Graphical abstract

Expanding horizons: The complex polycyclic hydrocarbon super-heptazethrene was synthesized using a strategy involving a selective multiple intramolecular Friedel–Crafts alkylation followed by oxidative dehydrogenation. Super-heptazethrene displayed a much larger diradical character (y₀) than heptazethrene.

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An accommodating host: The iminium-catalyzed 1,4-reduction of unsaturated aldehydes can be performed inside a supramolecular host. Only catalytic amounts of the supramolecular capsule are required. The intermolecular, noncovalent interactions inside the host system dramatically improve enantioselectivity for several amine catalysts.

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Publication date: 1 June 2016
Source:Tetrahedron Letters, Volume 57, Issue 22
Author(s): Komal G. Lalwani, Arumugam Sudalai
A new organocatalytic approach to the synthesis of ceramide trafficking inhibitor HPA-12 has been described starting from phenacyl bromide. The strategy involves chiral CBS reduction of γ-ketoester and proline-catalyzed α-amination reaction of aldehyde followed by reduction as the key chirality inducing steps.

Graphical abstract

Publication date: 20 April 2016
Source:Tetrahedron Letters, Volume 57, Issue 16
Author(s): Mitsuru Kitamura, Akihiro Ishikawa, Tatsuo Okauchi
Two chiral 2-azidoimidazolinium salts [(7aS)-3-azido-5,6,7,7a-tetrahydro-2-[(1R)-1-phenylethyl]-1H-pyrrolo[1,2-c]imidazolium hexafluorophosphate (2) and 2-azido-1,3-bis[(S)-1-phenylethyl]imidazolinium hexafluorophosphate (3)] were synthesized, and their structures were determined by X-ray single crystal structural analysis. Migratory amidation reaction of enol silyl ether with 3 proceeded, but good diastereoselectivity was not observed in the reaction.

Graphical abstract

Thiourea catalysts enhance the efficiency of the intermolecular [2+2] photocycloaddition of coumarin with tetramethylethylene by a combination of minimized aggregation, enhanced intersystem crossing (ISC), and altered excited-state lifetime(s). A third mechanistic pathway for thiourea-mediated photocatalysis has thus been revealed.

[Communication]
Nandini Vallavoju, Sermadurai Selvakumar, Barry C. Pemberton, Steffen Jockusch, Mukund P. Sibi, Jayaraman Sivaguru
Angew. Chem. Int. Ed., March 23, 2016, DOI: 10.1002/anie.201600596. Read article