N EWS OF THE W EEK
A CATALYTIC MERGER SYNTHESIS: Marriage of photoredox catalysis and organocatalysis creates new enantioselective reaction R
O
Aldehyde + O O Br O Alkyl bromide Organocatalyst, photoredox catalyst, visible light
O O O R
O
Enantioenriched -alkylated aldehyde R = hexyl
B
Y COMBINING two well-established ways
of activating molecules—photoredox catalysis and organocatalysis—chemists at Princeton University have achieved the first enantioselective α-alkylation of aldehydes (Science, DOI: 10.1126/science.1161976). Thanks to the new combined-catalysis concept, this once-elusive asymmetric reaction has become “operationally trivial,” according to the researchers, chemistry professor David W. C. MacMillan and postdoc David A. Nicewicz. Furthermore, they say, the combined-catalyst strategy could provide routes to a number of other enantioselective transformations. MacMillan and Nicewicz selected a ruthenium(II) bipyridine complex, Ru(bpy)32+, as their photoredox catalyst. Although this single-electron-transfer agent has been used in a number of areas, such as energy storage, it hasn’t been popular in organic synthesis. The Princeton chemists reasoned they could use the complex to harvest energy from ambient light, such as the
U.S. INVESTIGATES BAYER PLANT BLAST ACCIDENT: Federal officials look for
cause of fatal explosion
F
EDERAL INVESTIGATORS have begun examin-
ing the Aug. 28 explosion and fire at the Bayer CropScience plant in Institute, W.Va., that killed one worker and severely burned another. The facility, one of many located in West Virginia’s Kanawha Valley chemical corridor, produces crop protection chemicals. John Bresland, chairman of the Chemical Safety & Hazard Investigation Board (CSB), says it could take up to a year to complete the inquiry into the cause of the massive blast, which was felt several miles away in Charleston. “CSB is very concerned about an incident of this type because it took a life and had the potential for taking even more lives,” Bresland remarks. The explosion occurred in a section of the sprawling complex where Bayer makes the pesticide methomyl, which is used to ASSOCIATED PRESS
Flames shot into the air after an explosion last month at the Bayer CropScience plant in Institute, W.Va.
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overhead lamp in a fume hood, and thereby introduce a single electron into the catalytic cycle. Single-electron mechanisms are common in nature, MacMillan points out, but “as synthetic chemists we don’t typically consider one-electron pathways.” In the mechanism proposed by MacMillan and Nicewicz, the ruthenium complex generates an electrondeficient alkyl radical from an alkyl bromide. This radical combines with an enamine formed from the condensation of an aldehyde and a chiral amine catalyst. Subsequent hydrolysis generates an α-alkylated aldehyde. Because it only takes weak light, rather than high-energy ultraviolet light, to initiate the catalytic cycle, MacMillan thinks the process could be useful for manufacturing-scale syntheses. “MacMillan has managed to effect a challenging transformation with an efficient, versatile, mild, and environmentally benign process,” comments John M. Schwab, an organic chemist at the National Institute of General Medical Sciences, in Bethesda, Md. “I believe this will provide a new paradigm for asymmetric catalysis and at the same time open up the doorway to many new reactions that are currently unknown,” MacMillan says. To that end, his group has already applied the “photoredox organocatalysis concept” to a number of other transformations, including benzylation, trifluoromethylation, amination, and alkylcyanation of aldehydes.—BETHANY HALFORD
produce thiodicarb, a carbamate insecticide marketed under the trade name Larvin. Officials believe the blast involved a 4,000-gal tank that contained various waste products related to the manufacture of Larvin, including methyl isobutyl ketone, a highly flammable solvent, as well as hexane and dimethyl disulfide. “It was bad, but it could have been worse,” says Mike Dorsey, chief of homeland security and emergency management for the West Virginia Department of Environmental Protection. “What you had was a huge amount of fuel, so there was a really big fire.” Bayer says the unit is shut down and “will not be restarted in the future until its safe operation can be completely assured.” After CSB wraps up its investigation, OSHA will evaluate the findings and determine whether any federal safety standards were violated. In 2005, OSHA cited Bayer for multiple process safety deficiencies after an inspection of the Institute plant. The company paid $110,000 in fines to settle the case and promised to take corrective action. OSHA most recently inspected the facility in October 2007 and did not issue any citations. The last fatal chemical plant accident in the valley also occurred at the Institute complex. In 1994, an explosion at the plant, then owned by Rhône-Poulenc, killed one worker and a second died a decade later from injuries sustained in the accident.—GLENN HESS
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