Indolizines reduced derivatives

Figure 11 13C NMR data for (a) IV-methylisoindoIe, (b) its partially reduced derivative, (c) indolizine and (d) pyrrolidine...

Indolizines and their partially or wholly reduced derivatives were comprehensively reviewed in 1948 by Borrows and Holland.2 They were subsequently mentioned by Elderfield3 in 1952 and in more detail in 1961 by Mosby4 covering the literature up to the middle of 1958. The present review covers developments in indolizine and indolizidine chemistry since that time and includes publications listed in Chemical Abstracts up to the end of February 1977. 

The isomeric indolizines 38 and 39 seem to contradict these rules Compared to their dimethine derivatives 30 (n = 1) and 29 (n = 1) potentials are more positive by 0.1 V only and their Ksem s are quite similar. In the cases, however, the reduced form contains an azo group which changes to the less energetic azino group on oxidation, simultaneously transforming the indolizine into a pyri-dinium ring. 

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