A one-step electrochemical synthesis of 1,3-dinitro compounds from aromatic
and heteroaromatic aldehydes and nitromethane has been developed. in the p
rocedure. an electrogenerated base is prepared by cathodic reduction of air
-saturated nitromethane solutions. Then the aldehyde is added and allowed t
o react. The reaction presumably proceeds in thrice base-catalyzed steps: a
ddition of nitromethane to the aldehyde to form a nitroalcohol, dehydration
of the nitroalcohol to produce nitroolefin. and Michael addition of nitrom
ethane to the nitroolefin. The synthesis produces the 1.3-dinitro products
in very good yields when the aryl group is electron-donating in character.
For less strongly electron-donating groups, only moderate yields are obtain
ed and with electron-withdrawing groups the reaction tends to stop at the s
tags of the nitroalcohol. For purposes of comparison, four of the products
were prepared in a multistep synthesis with the last step being the cathodi
cally promoted Michael addition of nitromethane to the nitroolefin. It was
found that this last procedure was also successful in forming the 1,3-dinit
ro derivative from 2-thiophenecarbox-aldehyde and nitroethane in good yield
and ail three isomers of the product were separated and characterized. The
stereochemical identity of one isomer was proved by X-ray crystallography
whereas that of the other two was established by comparison of. nuclear mag
netic resonance spectra with those of the isomers of an analogous compound
of known stereochemistry. (C) 2000 The Electrochemical Society. S0013-4651(
99)06-092-9. All rights reserved.