Indolo quinolizine, ring system

A new route has been developed for the efficient formation of the variably substituted indolo[2,3-a]quinolizine ring system, starting from a properly substituted 2-piperidone (103, 104). For the preparation of octahydroindolo-quinolizine (1), the unsubstituted 2-piperidone 139 was treated with triethox-onium tetrafluoroborate. Then the corresponding lactim ether 140 was alkylated with 3-chloroacetylindole followed by a subsequent two-step reduction process and Bischler-Napieralski ring closure. Finally, reduction of the C=N bond afforded ( )-l (104). 

Synthesis of indolo[2,3-a]quinolizine ring system can be carried out by forming the C(12a)—C(12b) bond, and in fact, the availability of tryptamine, tryptophyl halides and the appro-... 

As discussed in previous sections, the indolo[2,3-fl]quinolizine ring exists in two resonance structures with the great contribution of zwitterionic form, evidenced by the colored nature and the high dipole moments of compounds of this type, as well as by their pH-dependent UV spectra. 6,7-Dihydro analogues, like the parent systems, can also be represented by the two mesomeric forms. Although these compounds are stable, they are readily protonated on the indole nitrogen atom and, in fact, these compounds are normally isolated and purified via their acid salts. 

The most important reaction is the aromatization of partially conjugated indolo[2,3-a]quinolizine compounds, a very useful synthetic route to the fully conjugated ring system. Catalytic dehydro-... 

Most of the compounds are named on the basis of indolizine and quinolizine nuclei with the exception of pyrrolo[l,2]naphthyridines, i.e. indolizine fused to a pyridine ring. In practice, two systems are used for numbering indolo[2,3-a]quinolizine examples shown below are indolo[2,3-ajquinolizine which is numbered according to the lUPAC recommendations also used in Chemical Abstracts, and tetrahydroindolo[2,3-a]benzo[9]quinolizine numbered following the generally accepted biogenetic numbering system. 

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