Organic & Biomolecular Chemistry Blog

In this HOT communication Jian Wang and colleagues at National University of Singapore report an efficient method to construct enantiomeric 2-amino-3-nitrile-chromenes through 2-iminochromenes and malonates. Using a thiourea catalyst Wang et al. rapidly construct the 2-amino-3-nitrile-chromene complexes via a multi-hydrogen-bond cooperative activation model.

For the details of their study download the communication today; it’s free to access for 4 weeks.

Organocatalytic conjugate addition promoted by multi-hydrogen-bond cooperation: access to chiral 2-amino-3-nitrile-chromenes
Wenjun Li, Jiayao Huang and Jian Wang
DOI: 10.1039/C2OB27102H

Cyclodextrins are macrocyclic oligomers of α-D-glucose. Their interaction with guest molecules is largely driven by the hydrophobic effect (the expulsion of water from the lipophilic cavity, into bulk, is entropically favourable).

In this HOT paper Cepeda and co-workers explore the solution phase behaviour of β-cyclodextrin/alkyltrimethylammonium bromide mixtures, varying the surfactant alkyl chain length from hexyl (C₆) to octadecyl (C₁₈).

Cepeda et al. employ the solvolysis of methoxybenzenesulfonyl chloride (MBSC) as a UV ‘handle’ to monitor the interaction between β-cyclodextrin and surfactant guests. In the presence of aggregated cationic surfactants, MBSC hydrolysis is hindered, owing to the reduced polarity of the micelle interior. MBSC solvolysis can be used to monitor the integrity of surfactant micelles and to calculate the concentration of unbound cyclodextrin.

In the presence of aggregated surfactants Cepeda et al. detect a significant concentration of ‘free’ β-cyclodextrin; the highest of which with decyl (C₁₀) and dodecyl (C₁₂) surfactants. This reflects the balance between the hydrophobic effect (smaller surfactant chains displace less water from the cyclodextrin cavity) and surfactant self-assembly (longer surfactant chains favour micelle formation).  The new model created to describe these interactions will aid the further development of commercial applications for these systems.

Competition between surfactant micellization and complexation by cyclodextrin
M. Cepeda, R. Daviña, L. García-Río, M. Parajó, P. Rodríguez-Dafonte and M. Pessêgo
DOI: 10.1039/C2OB26318A

Published on behalf of Steve Moore, Organic & Biomolecular Chemistry web science writer.

Researchers in Switzerland have discovered a fluxional molecule that dynamically resolves to a single metastable structural isomer.

Bullvalene is an intriguing molecule. A small polycycle with 10 carbons and 10 hydrogens, and an unusual property: it has no permanent chemical structure.

Its bonds are constantly rearranging through a seemingly endless series of Cope rearrangements. It’s estimated that there are over 1.2 million possible valence tautomers, and due to the rapidity of the conversions, all carbons and protons appear as equivalent on the NMR timescale.

Professor Jeff Bode and his group at ETH Zürich have an interest in these fluxional molecules and their potential uses as chemical sensors.

During a recent investigation into the racemisation of oligo-substituted members of the bullvalene family, they noticed some interesting behaviour in a sample of a tetrasubstituted bullvalene. A single isomer was spontaneously forming, and could be isolated from the mixture. This isomer was surprisingly stable, with a half-life of just over 4 hours at room temperature.

Now, tetrasubstituted bullvalenes have 1680 possible structural isomers and previous work has shown that the mixture is fully dynamic, so the appearance of just one isomer above all the others is pretty remarkable.

Their latest HOT PAPER builds on these results, and seeks to provide further information about the nature of this fascinating molecule.

Expand this blog to read more…

Thanks to developments in new phosphine ligands the area of C–Cl bond activation has made a lot of progress.

In this paper Shengming Ma and colleagues at Zhejiang University report recent results of the Suzuki coupling reaction of optically active α-chloroalkylidene-β-lactones derivatives using a LB-Phos ligand previously developed by the group. Using this method Ma et al. have prepared a series of optically active α-alkylidene-β-lactones in high ee.

Do you think that this protocol is a versatile method for the organic community to utilise? Read the paper today and let us know by leaving your comments on this blog.

Pd-catalyzed Suzuki coupling reaction of chloroalkylidene-β-lactones with LB-Phos as the ligand
Pengbin Li, Bo Lü, Chunling Fu and Shengming Ma
DOI: 10.1039/C2OB26365C

Researchers from Taiwan have developed an efficient organocatalytic enantioselective synthesis of spironitrocyclopropanes.

In this HOT communication Wenwei Lin and co-workers from National Taiwan Normal University describe the development of an efficient asymmetric pathway for the preparation of spironitrocyclopropanes from 2-arylidene-1,3-indandiones and bromonitroalkanes, catalysed by cinchona-derived bifunctional organocatalysts.

Lin et al. report reaction conditions which allow almost perfect diastereocontrol as well as outstanding enantiocontrol. As nitrocyclopropanes are found in various biologically active natural products and important precursors of bio-relevant cyclopropylamines this new method fills a real synthetic need.

Want to know more? Read the communication for free now! And it will remain free for the next 4 weeks.

An efficient organocatalytic enantioselective synthesis of spironitrocyclopropanes
Utpal Das, Yi-Ling Tsai and Wenwei Lin
DOI: 10.1039/C2OB26943K

Chemists from University of Cambridge, UK, have constructed a new class of multicomponent [2] and [3]catenanes utilizing up to four building blocks and three orthogonal interactions.

A major challenge in supramolecular chemistry is being able to harness several orthogonal weak interactions to generate structures with a similar complexity and functionality to those found in nature. This is because, as the variety of the building blocks and noncovalent interactions involved, control over the final structure becomes exponentially more difficult.

In this HOT Communication Miguel Á. Alemán García and Nick Bampos report a one-pot synthesis which uses multiple supramolecular components with distinctly different sets of noncovalent interactions to construct heteroleptic interlocked supramolecular metallomacrocycles.

This Communication is free to access for the next 4 weeks!

Synthesis of a four-component [3]catenane using three distinct noncovalent interactions
Miguel Á. Alemán García and Nick Bampos
DOI: 10.1039/C2OB26587G