NEWS OF THE W EEK
HYDROCHLORINATION REFORMATION SYNTHESIS: Transition-metal catalysis lets more substrates take part in a textbook reaction
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ITH THE HELP OF an unexpected reagent,
chemists Boris Gaspar and Erick M. Carreira at the Swiss Federal Institute of Technology, Zurich, have developed an alternative way to carry out a fundamental transformation in organic synthesis: the addition of hydrogen chloride to alkenes (Angew. Chem. Int. Ed., DOI:10.1002/anie.200801760). The cobalt-catalyzed process, which uses p-toluenesulfonyl chloride (TsCl) to deliver a chlorine atom, could streamline production of alkyl chlorides (sample reaction shown, TBDPS = tert-butyldiphenylsilyl). Alkyl chlorides are versatile building blocks for making materials and pharmaceuticals. The textbook reaction for directly adding HCl to alkenes generally requires strong acid as a catalyst. This makes the reaction difficult to use in the presence of acid-sensitive groups, which are abundant in many important intermediates. In reality, Carreira says, researchers therefore rarely use that reaction to convert alkenes to alkyl chlorides. To develop sound hydrochlorination conditions that would work around acid-sensitive groups, Gaspar and Carreira turned to cobalt catalysts. This strategy had already proven successful in Carreira’s group for preparing species such as azides and nitriles from olefins. Their search for an alternative source of Cl for such addition reactions turned up a surprising reagent—TsCl. Normally, this reagent transfers its toluenesulfonyl moiety in reactions, Carreira explains. But because the
team had used a related reagent in their olefin azidation and cyanation work, they decided to give TsCl a shot as a Cl-transfer reagent. The gamble paid off, despite there being little precedent for the reactivity they observed. In praising the researchers’ “exceptionally creative” approach, transition-metal catalysis expert John F. Hartwig of the University of Illinois, Urbana-Champaign, notes that few people would have imagined using TsCl in this way. The new procedure has the same selectivity as a traditional HCl addition, consistently placing the chlorine atom on the more substituted alkene carbon. Furthermore, the new conditions convert monosubstituted olefins, which typically fail to undergo conventional HCl addition, to the corresponding chlorides. The reaction also works O in the presence of some acid-sensitive O S Cl moieties. TBDPS
O
+
Cobalt catalyst
TBDPS
The current incarnation of the reaction is not enantioselective, but the catalyst system could be modified to make that possible, says chemist Matthew S. Sigman of the University of Utah. Sigman recently developed a palladium-catalyzed hydrochlorination reaction for styrenes, which do not react under Carreira’s conditions (Organometallics 2007, 26, 5680). The Zurich team is still working out the details of the reaction mechanism, particularly regarding the role of TsCl. But researchers are likely to try the method long before those results are announced, Hartwig says. “Given the recent interest in halogenated natural products and the wide utility of alkyl halides as synthetic intermediates, I expect this method to be used immediately,” he says.—CARMEN DRAHL
O Cl
INDUSTRY Former congressman Calvin M. Dooley selected to lead ACC chairman of the ACC board and chairman of Chemtura. Dooley, who served as a member of the House of Representatives from 1991 to 2004, representing the San Joaquin Valley area of California, has led GMA since it merged with the Food Products Association in January 2007. He was president of FPA for two years before the merger. While in Congress, Dooley was a founder of the New Democrat Coalition, an ideologically centrist, pro-business Dooley
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faction within the Democratic Party. Dooley says he approaches advocacy with a business perspective and looks forward to building broadbased coalitions. “There is a great deal of commonality in the issues being addressed at ACC and those in which I am currently involved,” he notes. Gerard departs on Sept. 1 to head up the American Petroleum Institute, which lobbies on behalf of the oil and natural gas industry.—GLENN GMA
The American Chemistry Council has selected former Democratic congressman Calvin M. (Cal) Dooley to succeed Jack N. Gerard as president and chief executive officer. Dooley is currently president of the Grocery Manufacturers Association (GMA), a trade group representing food manufacturers. He will take over the leadership of ACC, which represents major U.S. chemical manufacturers, on Sept. 8. “Cal’s knowledge of industry, his excellent bipartisan reputation on Capitol Hill, his savvy business sense, and his political acumen make him a great choice to lead our association,” says Robert L. Wood,
HESS
