NEWS OF THE WEEK
ETHANOL: President Obama
wants U.S. leadership; EPA works on life-cycle analysis
T
HE OBAMA ADMINISTRATION has launched
a federal program to support U.S. biofuels R&D and commercialization, part of which is already raising concerns. “If we are to be the leader in the 21st-century global economy, then we must lead the world in clean energy technology,” President Barack Obama said when announcing the new biofuels program last week. The program creates an interagency working group that will coordinate government agencies involved in biofuels R&D, market development, production, and transportation. It also provides nearly $800 million to speed up advanced biofuels R&D and to spur commercial-scale biorefinery demonstration projects. A controversial part of the program, however, is an EPA draft proposal that SHUTTERSTOCK
An EPA life-cycle analysis has found that using corn to make ethanol may not reduce greenhouse gas emissions.
NEW WAY TO PROTECT UNSTABLE BORON REAGENTS
CH3N O O
B O O
ORGANIC SYNTHESIS: Masked boronates
make 2-pyridyl coupling possible
MIDA boronate Aqueous base
A
NEW CARBON-CARBON coupling technique
provides a route to compounds that are currently difficult to synthesize. The approach eases access to 2-pyridyl and other heterocyclic derivatives that are of key importance, especially in drug discovery, but have been particularly challenging synthetically. B(OH)2 Chemists often form C–C links by using Stille or Suzuki coupling reactions. But Stille reactions use toxic Boronic acid tin reagents, and Suzuki reactions use boronic acid intermediates that tend to be unstable. Extensive efforts Aqueous Pd catalyst, base have been made to reduce the instability of Suzuki borCl onates, but most approaches have major limitations. One of the most promising tactics has been the use of stable organotrifluoroborates in place of unstable boronates, an approach developed in the past few years by orAir-stable MIDA boronates release unstable boronic acid intermediates slowly, ganic chemistry professor Gary enabling the intermediates to combine with A. Molander and coworkers at reagents before they decompose. the University of Pennsylvania WWW.CEN-ONLINE.ORG
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lays out a strategy, required under a 2007 energy law, to produce 36 billion gal of biofuels by 2022. The law sets targets of 15 billion gal of conventional ethanol, 16 billion gal of cellulosic ethanol, and 5 billion gal of advanced biofuels and biodiesel. According to the law, a biofuel must achieve at least a 20% reduction of the greenhouse gas emissions that would have resulted from use of petroleum-based fuel, as determined by lifecycle analyses. Similarly, biodiesel or advanced biofuels must achieve a 50% reduction in CO2 emissions, and cellulosic biofuels, a 60% reduction. The law’s requirement of a life-cycle analysis of biofuels reflects a growing concern that ethanol may result in higher CO2 emissions due to land-use practices, such as clearing rain forest to grow energy crops. Indeed, EPA’s proposed method for conducting life-cycle analyses has found that CO2 emissions from conventional ethanol production fall short of the 20% threshold in some instances, such as when coal or natural gas is used to power a biofinery. Legislators from farm states and the ethanol industry say that EPA’s proposal is inaccurate and that they do not support it. In a briefing last week, EPA Administrator Lisa P. Jackson said the proposal lays out pathways to reduce the carbon footprint for different biofuels. She also noted that 15 billion gal of ethanol are exempt from the biofuel definition. The agency will accept comments over the next 60 days.—JEFF JOHNSON
and elsewhere. But the trifluoroborate technique still doesn’t work well in some cases, such as with 2-pyridyl couplings. Now, grad students David M. Knapp and Eric P. Gillis and assistant professor of chemistry Martin D. Burke of the University of Illinois, Urbana-Champaign, have further expanded Suzuki coupling by developing a method that uses N-methyliminodiacetic acid (MIDA) to protect unstable boronates (J. Am. Chem. Soc., DOI: 10.1021/ ja901416p). MIDA boronates are easy to synthesize and stable, and they release unstable boronic acid intermediates slowly, enabling Suzuki coupling to occur before the intermediates decompose. The technique makes it feasible to carry out 2-pyridyl and other heterocyclic couplings. Lawrence G. Hamann, executive director for Global Discovery Chemistry at Novartis, in Cambridge, Mass., comments that MIDA boronates tolerate a substantial range of reaction types and that 2-pyridyl MIDA boronates in particular “are a major advance, as the trifluoroborate methodology does not work here.” He notes that 2-pyridyl moieties are “ubiquitous in many druglike molecules.” “MIDA boronate stability, reliability, and ease of use, in conjunction with the ability to mitigate the use of toxic tin-derived reagents, will accelerate the broad incorporation of this tool into synthetic strategies,” adds Peter T. Meinke, senior director of medicinal chemistry at Merck & Co., in Rahway, N.J.—STU BORMAN
MAY 11, 2009
ADAPTED FROM J. AM. CHEM. SOC.
SUPPORTING BIOFUELS
