CARBOXYLATION MADE SIMPLE
KO
GREEN CHEMISTRY: Method directly
adds CO2 to aromatic C–H bonds
A
STRAIGHTFORWARD and environmentally
friendly technique uses carbon dioxide to convert acidic C–H bonds in aromatic compounds into acid and ester groups. The reaction could make aromatic acids and esters more readily available for use in organic synthesis, drug discovery, and other applications. The reaction uses N-heterocyclic carbene (NHC) gold(I) catalysts, which are stable and recyclable and require no special handling. It was developed by postdoctoral fellow Ine I. F. Boogaerts and chemistry professor Steven P. Nolan of the University of St. Andrews, in the U.K. (J. Am. Chem. Soc., DOI: 10.1021/ja103429q). Unlike existing ways to carboxylate aromatic C–H bonds, the reaction proceeds at room temperature and moderate pressure, and its only by-product is water. “This is probably the first example of taking an unactivated C–H bond and directly converting it into a carboxylic acid group,” comments Tomislav Rovis of Colorado State University, a specialist in NHC and transition-metal catalysis. “It’s surprising that the reaction conditions are so mild. The scope is limited to acidic aromatics, but it’s neat chemistry that could stimulate other work in this area.” “It’s a striking transformation, and we’ll see how general it becomes” as its applicability is further investigated, says John F. Hartwig of the University of Illinois, UrbanaChampaign, a C–H bond functionalization specialist. “It’s a breakthrough in using a base as catalyst for carboxylation and therefore has potential for development.”
O
N
N N
O
C
H O Oxazole
Au
N
OH
Carboxylate product
N-Heterocyclic carbene gold(I) hydroxide catalyst H2O
KOH
ADAPTED FROM J. A M. C HE M. SOC.
NEWS OF THE WEEK
CARBOXY-GO-ROUND N
Catalyst carboxylates the most acidic C–H bond on oxazole.
N Au O
O
O
C
CO2
N
N Au
N
O
N
C–H bonds in oxazoles, chlorinated or fluorinated benzenes, and other aromatic compounds are typically carboxylated with powerful bases like alkyllithiums and Grignard reagents or in transition-metal-catalyzed reactions. The former reactions are stoichiometric, require anaerobic conditions, and produce toxic byproducts. The latter use nonrecyclable catalysts, need a C–H bond prefunctionalization step, and require forcing conditions (inert atmospheres, high temperatures and pressures, and large amounts of catalyst). In the new reaction, the recyclable catalyst activates the most acidic aromatic C–H bond, and CO2 inserts at that position. C–H prefunctionalization is not necessary. “Nothing of the sort has been so simply done,” Nolan says. “We have hit on something interesting here and are currently exploring how general such functionalizations can be.”—STU BORMAN
CROP PROTECTION Makhteshim Agan to buy Albaugh in $1.3 billion deal Leading off-patent crop protection chemical specialist Makhteshim Agan Industries has agreed to buy Iowa-based Albaugh in a deal valued at $1.3 billion. The transaction is expected to close by the end of the year pending government approvals. It will boost the reach of MAI, based in Israel, in the Americas and augment its manufacturing capabilities. Albaugh, the largest generic crop protection chemical firm in North America, will swell the Israeli firm’s annual sales by about $1.0 billion to about $3.1 billion, on the basis of 2009 results. It brings manufacturing sites in the U.S.,
Brazil, Mexico, and Argentina, as well as a joint venture in China that produces N(phosphonomethyl) iminodiacetic acid, a raw material for the weed killer glyphosate. Albaugh, which has about 3,000 employees, is a significant manufacturer of glyphosate, as well as the herbicides 2,4-D and dicamba, various insecticides, fungicides, and plant-growth regulators. According to MAI, the acquisition will put it significantly ahead of its two nearest generic crop protection chemical competitors, Australia’s Nufarm and Japan’s Sumitomo Chemical, which had 2009 sales of $1.8 billion and $1.4 billion,
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respectively. In April, Sumitomo acquired a 20% interest in Nufarm. Dennis Albaugh, CEO and sole owner of the U.S. firm, will chair MAI’s North America operations. Under the terms of the deal, MAI will pay with $340 million in cash, $455 million in notes, and about $200 million in MAI stock. It will also assume $280 million in Albaugh’s debt. Roni Biron, who follows MAI’s stock for UBS Investment Research, points out that in addition to boosting MAI’s Americas presence, the transaction will bring MAI “low-cost production sites and access to large growers.”—MARC REISCH
