To make vicinal diamines, in which neighboring carbons each have an attached amine group, chemists generally expose alkenes to harsh chemical oxidants, which can produce environmentally toxic by-products. Now, researchers have replaced those harsh reactants with a metal catalyst and some electrical current to create a safer and less wasteful synthetic route to 1,2 diamines, functional groups that crop up in many pharmaceuticals and stereoselective catalysts (Science 2017, DOI: 10.1126/science.aan6206).
The reaction combines abundant starting materials—alkenes and sodium azide—with a manganese catalyst inside a simple electrochemical cell that has a carbon anode and platinum cathode. It adds two equivalents of azide to the alkene C=C bond, generating a 1,2-diazide that can then easily be reduced to a 1,2-diamine.
Although electrochemical set-ups are not common in synthesis labs, they are starting to attract more attention from organic chemistry research groups. One advantage of electrosynthesis is that it gives chemists the ability to fine-tune their reactions.
For instance, each reaction component has a measurable electrical oxidation potential. With electrosynthesis, you can dial-in the voltage needed to achieve that potential to target a component for reaction without disturbing other functional groups, says Cornell University’s Song Lin, who led the work.
The electrochemical diazidation reaction was compatible with a broad range of starting materials, some of which typically don’t work well with traditional ways of making diazides. These compounds include alkenes with groups sensitive to oxidation and nucleophilic substitution and even bulky, tetrasubstituted alkenes.
When Lin and his team studied the mechanism of the new reaction, they found that a key, highly oxidizable manganese-azide intermediate likely forms. Once the species has been oxidized, the researchers propose, it can act as an azide transfer agent to produce the 1,2-diazide product along with benign side products, such as hydrogen gas and sodium acetate.
“This is a remarkably useful transformation that exhibits broad scope and functional group tolerance to access useful diamine precursors,” says organic chemist Phil Baran of Scripps Research Institute California. “In terms of sustainability and simplicity, it’s hard to beat an electrochemical approach, so I expect that this cool reaction will find use right away in a variety of settings.”
Lin’s group is now in talks with potential industrial partners to develop the reaction into a scalable protocol.