Issue Date: April 25, 2011
Without a functional group to grab onto, chemists can’t do much with alkanes other than burn them. Now, researchers in Japan have developed a metal-free method to outfit these hydrocarbons with amines (Science, DOI: 10.1126/sci ence.1201686), thus making them available for further reactions.
The room-temperature reaction is regioselective and offers a more environmentally friendly route than similar transformations that use hypervalent iodine reagents with metal catalysts. The reaction makes use of an N-triflylimino-λ3-bromane compound, which inserts nitrogen functionality into C–H bonds to give triflyl-substituted amines. The hypervalent bromine reagent has a marked selectivity for tertiary C–H bonds over secondary ones but leaves primary C–H bonds alone.
The research team, led by Masahito Ochiai of the University of Tokushima and Waro Nakanishi of Wakayama University, previously developed the hypervalent bromine reagent to transform alkenes into aziridines—a reaction that had already been done with hypervalent iodine and a metal catalyst. If the hypervalent bromine could replace the hypervalent iodine and metal catalyst in that reaction, the researchers reasoned, it could also replace those reagents for aminating aliphatic C–H bonds.
Ochiai says the hypervalent bromine reagent is fairly stable in the solid state, lasting up to a month in the refrigerator without decomposition. Its preparation is simple, he says, but because it uses bromine trifluoride and liberates HF gas, it demands certain safety precautions. “Care should be taken in handling bromine trifluoride because it will react violently with most organic compounds,” Ochiai warns.
Philippe Dauban, a chemist at France’s Institut de Chimie des Substances Naturelles, who has worked on aminations using hypervalent iodine reagents and transition metals, notes the hypervalent bromine reagents “might provide new opportunities” for aminations. But he points out that they are not without their limitations. For example, he says, using alkanes as solvents could be problematic.
“The problem of efficient selective amination of alkanes has not been solved by this study,” Dauban says, “but it clearly shows us new avenues to explore.”
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