Synthesis of 9,10-Dimethoxy-1,2,3,4,6,7-hexahydro-2,6-methano-11bH-benzo [a] quinolizine

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A synthesis of9,10-dimethoxy-1,2,3,4,6,7-hexahydro-2,6-methano-11bH-benzo [a]-quinolizine having a new ring system was described. Thus, dl-N-benzyl-3-(3,4-dimethoxyphenyl) alanine ester (VI) was condensed with succinic anhydride followed by esterification to give amido-ester (IX), which on being cyclized with phosphoryl chloride under reflux furnished the corresponding dihydroisoquinoline derivative (X) isolated as iodide. When the latter was reduced with sodium borohydride-methanol, there were obtained α-and β-isomers of tetrahydroisoquinoline derivative (XI)ca. in a ratio 5 : 1. On being cyclized with sodium hydride-toluene they gave one and the same cyclic β-ketoester (XII), which was condensed with ethyl bromoacetate followed by ketone fission to yieldγ-ketoester (XV). An alternative route XV was also discribed. XV was then reduced with sodium borohydride and the resultant alcohol (XVIII) was chlorinated to give the chloride (XIX), which was reduced with lithium aluminum hydride-tetrahydrofuran. The reduction product was directly tosylated and worked up properly furnishing the cyclized product, which was characterized as perchlorate. On being reduced catalytically the latter furnished the ultimate product (I). A smaller quantity of by-product was also obtained in the final cyclization step, to which structure (I-B) was postulated.
1964-12-25