SYNTHESIS OF EMETINE AND RELATED COMPOUNDS .6. IMPROVEMENTS IN 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]QUINOLIZINE-2-ONES . FORMATION OF SOME RELATED DIAZABICYCLO[3,3,1]NONANES

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-methanodi-isoquino[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).