The synthesis of emetine and related compounds. Part VI. Improvements in the synthesis of 3-alkyl-1,3,4,6,7,11b-hexahydro-9,10-dimethoxybenzo[a]quinolizin-2-ones and 3-alkyl-1,2,3,4,6,7,12,12b-octahydroindolo[2,3-a]quinolizin-2-ones. Formation of some related diazabicyclo[3,3,1]nonanes

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A simplified procedure is reported for the almost quantitative conversion of the dihydroisoquinoline(II) into the benzo[a] quinolizines (I; R = alkyl). A by-product formed in the preparation of the 3-unsubstituted compound (Ic) is assigned the pentacyclic structure (VII). 3,4-Dihydro-β-carboline condenses with Mannich bases in the presence of carbon dioxide to give the indolo[2,3-a]quinolizines (XII; R = alkyl) in good yield. The unsymmetrical di-Mannich base (XIII) condenses with two molecules of the dihydroisoquinoline (II) to give the 9,18-methanodiisoquino[2,1-a : 1′,2′-d][1,5]diazocine (XV); the symmetrical di-Mannich base (XVI), or the 4-oxopiperidinium salt (XIX), gives the substituted 9,18-methanodi-isoquino[2,1-a: 2′,1′-e][1,5]diazocine (XVIII), together with a trace of the dipentacyclic ketone (XXII).