The cathodic cleavage of the 4-nitrobenzyloxycarbonyl group from amine derivatives in aprotic conditions
Abstract
The cathodic cleavage of the 4-nitrobenzyloxycarbonyl group from the urethane derivatives of four amines, two primary and two secondary, in dimethylformamide is reported. It is shown by cyclic voltammetry that the derivatives are reduced in several steps. The first occurs at about –1.1 V vs. s.c.e. and on the timescale of cyclic voltammetry is a reversible 1 e process. On the timescale of several minutes, however, the anion radicals are unstable and cleavage of the 4-nitrobenzylcarbonyl group occurs. Coulometry then shows the reduction to be a 2e process and free amines are isolated in above 80% yields. Hence reduction at –1.2 V in aprotic conditions seems to be the basis of a straightforward procedure for the removal of 4-nitrobenzyloxycarbonyl group and this increases the scope for the use of this protecting group in the synthesis of large molecules. The influence of proton donors on the reduction of the urethane derivatives is also discussed.