Benzo‐ and indoloquinolizines. XII —carbon‐13 n.m.r. study of the conformation of the 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9a H ‐pyrido[1,2‐ f ]phenanthridine isomers

The influence of the configuration and the conformation on the 13 C n.m.r. spectrum of 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9a H ‐pyrido[1,2‐ f ] phenanthridine was investigated. These observations, coupled with the low temperature spectrum allowed us to confirm the trans ‐ syn ‐ cis as the preferred conformation for one of the four isomers. At −40°C, 2–3% of another conformer could be detected and identified as the cis ‐ anti ‐ cis ‐2.