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Enantioselective synthesis of cyclic carbamimidates

17 May 2011

A racemic Au(I)-catalysed three-component reaction has been developed by US scientists to prepare cyclic carbamimidates from imines, terminal alkynes and sulfonylisocyanates. This reaction exploits the carbophilic π-acidity of gold catalysts to first activate an alkyne toward deprotonation and then to activate the internal alkyne generated toward intramolecular O-cyclisation.

Unlike similar previously reported multicomponent gold-catalysed reactions, the stereocentre generated during the alkynylation is preserved in the product. This trait was exploited by developing an enantioselective variant, using an unusual trans-1-diphenylphosphino-2-arylsulfamidocyclohexane ligand.

Graphical abstract: Enantioselective synthesis of cyclic carbamimidates via a three-component reaction of imines, terminal alkynes, and p-toluenesulfonylisocyanate using a monophosphine gold(i) catalyst

Moderate to excellent levels of enantioselectivity were obtained using a variety of N-arylbenzylidene anilines.

Find out more:
M J Campbell and F D Toste, Chem. Sci., 2011, DOI: 10.1039/c1sc00160d

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Recognising the best organic chemistry

12 May 2011

a trophy On Monday I attended the RSC Organic Division Awards Symposium at the University of Cambridge. Organised by Chemical Science Associate Editor Matthew Gaunt, the symposium recognised three 2010 RSC award winners for their impressive contributions to organic chemistry

First up was Bader Award winner Professor Kevin Booker-Milburn (University of Bristol, UK) who stressed the ongoing importance of curiosity in organic synthesis. He discussed his research on organic photochemistry, in particular how his group had managed to scale up organic photochemistry reactions using continuous flow reactors.

Next Hickinbottom Award winner Dr Matthew Clarke (The University of St Andrews, UK) split his approaches to controlling enantioselectivity in asymmetric synthesis into the sensible (asymmetric hydroformylation); the silly (using supramolecular synthesis to make libraries of catalysts); the scientific (rational design of hydrogenation catalysts); and the serendipitous (palladium-catalysed hydroxycarbonylations).

Last, but by no means least, Professor Dieter Enders (RWTH-Aachen, Germany), winner of the Robert Robertson award, discussed his work on asymmetric organocatalysis and revealed he has been an RSC member since before I was born.

Many thanks to Martin Swarbrick from the Organic Division for presenting the prizes, Matthew Gaunt for the organisation and, of course, the three speakers for delivering excellent and enjoyable lectures.

Also of interest:
N-heterocyclic carbene catalysed asymmetric cross-benzoin reactions of heteroaromatic aldehydes with trifluoromethyl ketones
Dieter Enders, André Grossmann, Jeanne Fronert and Gerhard Raabe, Chem. Commun., 2010, 46, 6282-6284

On the rate-determining step and the ligand electronic effects in rhodium catalysed hydrogenation of enamines and the hydroaminomethylation of alkenes
José A. Fuentes, Piotr Wawrzyniak, Geoffrey J. Roff, Michael Bühl and Matthew L. Clarke, Catal. Sci. Technol., 2011, DOI: 10.1039/C1CY00026H

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Hardy MOFs endure extreme conditions

03 May 2011

The most chemically and thermally stable metal-organic frameworks (MOFs) yet have been made by a team in the US. The MOFs could surpass zeolites as industrial catalysts.

Natural zeolites are porous alumina-silicate rocks used as catalysts in industrial processes. However, their pore sizes and surface functionalisations are difficult to alter, which limits their performance. MOFs – made by joining up metal oxide clusters with linking organic molecules – have similar structures to zeolites and are therefore of interest as alternatives. Until now, they have not been robust enough to withstand the conditions that zeolites undergo during industrial processes. Traditionally, MOFs have only been stable in temperatures up to 500 degrees Celsius, have low chemical stability and some even fall apart in water.

Jeffrey Long from the University of California, Berkeley, and colleagues have made MOFs that can withstand temperatures of 510 degrees Celsius and a pH range of 2 to 14. They made the MOFs by reacting a metal salt, such as nickel chloride or nickel nitrate, with trispyrazolylbenzene. The organic molecules were deprotonated and the functional groups were bound to the metal to create a three-dimensional network.

Scheme of formation of MOFs

Find out more by reading the full news story in Chemistry World and downloading Professor Long’s Chemical Science Edge article.

Also of interest:
Modifying MOFs: new chemistry, new materials
Seth M. Cohen, Chem. Sci., 2010, 1, 32-36

Hydrogen storage and carbon dioxide capture in an iron-based sodalite-type metal–organic framework (Fe-BTT) discovered via high-throughput methods
Kenji Sumida, Satoshi Horike, Steven S. Kaye, Zoey R. Herm, Wendy L. Queen, Craig M. Brown, Fernande Grandjean, Gary J. Long, Anne Dailly and Jeffrey R. Long, Chem. Sci., 2010, 1, 184-191

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Register now for ISACS meetings to receive early bird discount

15 Apr 2011

– Call for posters – deadline 6 May 2011
– Early bird registration – deadline 6 May 2011
– Registration – deadline 3 June 2011
www.rsc.org/isacs4

– Call for posters – deadline 27 May 2011
– Early bird registration – deadline 27 May 2011
– Registration – deadline 24 June 2011
www.rsc.org/isacs5

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Molybdenum sulfide hydrogen evolution catalysts

14 Apr 2011

Amorphous molybdenum sulfide films are highly active hydrogen evolution catalysts, say researchers from Switzerland.

Xile Hu and colleagues made the catalysts from relatively cheap and abundant elements. The catalysts offer significant advantages over noble metal catalysts, they say. The catalysts can be easily prepared in a procedure that is amenable to large scale manufacture, they work in water and are compatible with a wide range of pHs.

‘Our results provide new opportunities for the development of renewable and economic hydrogen production technologies,’ says the team.

Read more for free in Chemical Science or check out the news story on the EPFL website.

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Expanding the pleuromutilin class of antibiotics by de novo chemical synthesis

14 Apr 2011

US scientists have made new pleuromutilin-like compounds that show promise as leads for the development of new antibiotics. Erik Sorensen and colleagues made the compounds in approximately 11 steps from 3-allylcyclopent-2-enone by a strategy featuring sequential carbonyl addition reactions.

They found that the compounds displayed activity against Mycobacterium tuberculosis.

Graphical abstract: Expanding the pleuromutilin class of antibiotics by de novo chemical synthesis

‘As we move forward in our effort to expand the structural and stereochemical diversity of the pleuromutilin class of antibiotics, there is a high likelihood that we will discover additional, new compounds with promising activity against M. tuberculosis and possibly resistant strains of TB as well as other bacteria,’ say the team.

Download the article, which is free to access in Chemical Science.

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Molecular fridge can reach millikelvin

07 Apr 2011

Molecular cooler Scientists have laid the foundations for a high-performance ‘molecular fridge’ capable of reaching temperatures within a few thousandths of a degree of absolute zero (0K) with a high degree of efficiency. Such ultracoolers could have applications in areas such as ultra-low temperature physics, where alternative technologies such as those that rely on expensive and rare helium-3 could be unsuitable or too costly.

The system relies on a phenomenon called the magneto-caloric effect, where the removal of a magnetic field from a ferromagnetic material causes a drop in temperature. The key to achieving a high magneto-caloric effect is to have a material with many unpaired electrons, all of whose spin states are aligned.

Euan Brechin from the University of Edinburgh in the UK, Keith Murray from Monash University in Australia and Marco Evangelisti from the University of Zaragoza in Spain and their colleagues designed a molecule based on gadolinium and copper, which can be cooled to a few millikelvin.

Read the rest of the news story on the Chemistry World website and download the group’s Chemical Science Edge article for free.

Think this is cool? Let us know by leaving your comments below.

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Hydrogenation in flow – scalable, economical and safer

06 Apr 2011

Hydrogen is explosive – it’s one of the first things children learn in their chemistry classes.

This is a serious drawback for the catalytic hydrogenation of multiple bonds, one of the most widely used reactions in organic synthesis. But now Steven Ley and colleagues at the University of Cambridge, UK, have improved the safety profile of both homogeneous and heterogeneous catalytic hydrogenations using flow chemistry.

In their Chemical Science Edge article, the group describe their ‘Tube-in-Tube’ reactor/injector and a novel computer-assisted bubble counting technique to measure the levels of hydrogen uptake.

Graphical abstract: Hydrogenation in flow: Homogeneous and heterogeneous catalysis using Teflon AF-2400 to effect gas–liquid contact at elevated pressure

Read the article for free and leave your comments below. If you’d like to be seen with the best, submit to Chemical Science today.

Also of interest:
Ten key issues in modern flow chemistry – a ChemComm Highlight in Chemistry article by Andreas Kirschning and colleagues

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A Sustainable Global Society: How Can Materials Chemistry Help?

31 Mar 2011

A high profile white paper A Sustainable Global Society: How Can Materials Chemistry Help? was launched internationally on 27 March.

The output of the Chemical Sciences and Society Summit (CS3) 2010, which took place in London, September 2010, outlines five key areas in which materials chemists, through collaboration with other scientists, industry and policy makers, can seize exciting opportunities to address global challenges. This project was driven by the RSC and is a collaboration between the chemical societies of China, Germany, Japan, the US, the UK and national funding bodies. Around 30 leading materials chemists from the participating nations participated in CS3 2010 and the white paper is a reflection of the outcome of the summit, in particular their view of the future direction for materials chemistry.

View the official website of the white paper.

Read the 27 March press release.

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Total synthesis of (–)-3-demethoxyerythratidinone

28 Mar 2011

US scientists have reported the preparation and synthetic applications of sulfinimines derived from benzoquinone monoketals. The method provides the first direct access to a variety of enantioenriched 4-aminocyclohexadienones, which possess synthetic handles for further elaboration to alkaloid natural products, say the researchers.

Graphical abstract: Benzoquinone-derived sulfinyl imines as versatile intermediates for alkaloid synthesis: Total synthesis of (–)-3-demethoxyerythratidinone

They demonstrated the the utility of the method in a short, enantioselective total synthesis of the natural product 3-demethoxyerythratidinone.

Read more:
Benzoquinone-derived sulfinyl imines as versatile intermediates for alkaloid synthesis: Total synthesis of (–)-3-demethoxyerythratidinone
K V Chuang, R Navarro and S E Reisman, Chem. Sci., 2011, DOI: 10.1039/c1sc00095k

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