Enamine trapping with the oxidation of nicotine and analogues

Various N-tertiary pyrrolidine derivatives 1 and 6-9 bearing voluminous substituents in 2-position react with Hg(II)-EDTA under double dehydrogenation and an atypical direction to the secondary C-5 with formation of the corresponding lactams 2 and 12-15. The primary products of a two electron withdrawal cannot be isolated. By addition of substituted benzaldehydes b-d as trapping reagents to the Hg(II)-EDTA solution additionally are received condensation products of the type of benzylidene lactams 1b-d, 6b,c and 7b-9b. Here the total yield of isolated products increases, while simultaneously the yield of unsubstituted lactams of the type 2 and 12-15 decreases. Therefore the atypical direction of dehydrogenation with the trapping aldehydes is the same as with the lactam forming pyrrolidines. Additionally the detection of the enamine species in the first stage of dehydrogenation with following reaction to the condensation product is secured. The (E)-configuration of 1b is confirmed by the chemical shift of the proton alpha-H and the 19F/13C-coupling constant of C-4 by direct comparison with its (Z)-isomer 27. The similar signal dates of the enone protons in the other prepared benzylidene lactams 1c,d, as well as 6b,c and 7b-9b verify also the (E)-configuration.