N EWS O F T H E W E E K
CROSS-COUPLING MADE EASY ORGANIC SYNTHESIS: Iron catalysis
simplifies coupling of aryl and alkyl Grignard reagents
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R + R′ X = Cl, Br
X
alkyl halides to form substituted aryl compounds—one of the most indispensable types of reactions in organic synthesis—has just gotten easier thanks to a new procedure that combines the formation of Grignard reagents and iron catalysis in one-pot reactions (Angew. Chem. Int. Ed. 2009, 48, 607). The approach, designed by Waldemar M. Czaplik, Matthias Mayer, and Axel Jacobi von Wangelin of the University of Cologne, in Germany, builds on previous iron-mediated Grignard Fe(MgX)2 R′ cross-coupling methods. But rather than separately R preforming large amounts of hazardous organomagnesium reagents, as in standard Grignard coupling reactions, the new sequence forms Grignard reagents in situ. It also avoids the higher cost and toxicity problems associated
2011, INTERNATIONAL YEAR OF CHEMISTRY COMMEMORATION: United Nations
will celebrate chemistry
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HE UNITED NATIONS General Assembly has passed a resolution formally declaring 2011 as the International Year of Chemistry. Ethiopia, which is the host country for the Federation of African Societies of Chemistry, submitted the resolution calling for the year, which will highlight the achievements of chemistry and its contributions to humanity. “The International Year of Chemistry will give a global boost to chemical science in which our life and our future are grounded,” says Jung-Il Jin, president of the International Union of Pure & Applied Chemistry (IUPAC) and a professor of chemistry at Korea University, in Seoul, South Korea. “We hope to increase the public appreciation and understanding of chemistry, increase young people’s interest in science, and generate enS H U T T E RSTO C K
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IRECT CROSS-COUPLING of aryl halides with
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with palladium and nickel cross-coupling catalysts. For a typical reaction, the researchers add FeCl3 dissolved in tetrahydrofuran to a flask containing magnesium turnings. They also add tetramethylethylenediamine to serve as a ligand for stabilizing organometallic intermediates. They then add aryl and alkyl bromide reagents and allow the reaction to run for three hours at 0 ºC before quenching it and isolating the product. Iron catalyzes the in situ formation of the Grignard reagents, Jacobi von Wangelin explains. Although the exact details aren’t yet known, it appears that alkyliron and arylmagnesium species are at work, he says. As these reagents form, the active cross-coupling catalyst, which the researchers believe is Fe(MgX)2, where X is Cl or Br, also forms. The team used a variety of aryl-alkyl and alkenyl-alkyl combinations to make coupling products with up to 81% yield. Slow formation of the Grignard reagents combined with the rapid iron-catalyzed coupling step keeps the concentration of reactive organomagnesium intermediates low throughout the reaction, Jacobi von Wangelin says. This approach to aryl-alkyl cross-couplings “nicely illustrates a general trend in today’s catalytic organic chemistry: to achieve high selectivity with simple, readily available reagents in a safe and environmentally benign manner,” notes Carsten Bolm of RWTH Aachen University, in Germany. The Cologne team’s reaction is effectively “cross-coupling made easy,” Bolm says.—STEVE RITTER
thusiasm for the creative future of chemistry,” he adds. IUPAC has established a management panel that will work with chemical societies; the UN Educational, Scientific & Cultural Organization (UNESCO); and others to plan and implement activities during the year. “We are delighted that Ethiopia has provided international leadership to bring this forward, first to the UNESCO executive board and then to the UN General Assembly this fall,” says Peter Mahaffy, professor of chemistry at King’s University College, in Edmonton, Alberta, and chair of IUPAC’s Committee on Chemistry Education. The UN resolution, he says, was formally sponsored by more than 35 countries and supported by many others. “The American Chemical Society and the National Academy of Sciences both played a very helpful role in winning support in the U.S.,” Mahaffy notes. “This designation by the United Nations is truly exciting,” ACS President Thomas H. Lane says. “It is an opportunity for our world to learn more about the transforming powers of chemistry.” Lane says ACS will make its expertise, networks, and National Chemistry Week experience available to help ensure a successful year. “Further,” he adds, “we will help provide opportunities for Nobel Laureates, eminent scientists, teachers, outstanding young chemistry students, and chemistry communities around the world to demonstrate how people’s lives are improved through chemistry.”—GLENN HESS
JANUARY 12, 2009
