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Paper | Regular issue | Vol 26, No. 11, 1987, pp.2949-2957
Published online, 1st January, 1970
DOI: 10.3987/R-1987-11-2949
Quinolizidines. XXIII. An Alternative Synthetic Route to Benzo[a]quinolizidine-type Alangium Alkaloids from Ethyl Cincholoiponate

Tozo Fujii, Masashi Ohba, Kaori Shimohata, and Shigeyuki Yoshifuji

*Faculty of Pharmaceutical Scicences, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-0934, Japan

Abstract

The trans lactam acid (+)-XX was isolated in good yield in the form of the 4-methoxybenzyl ester (+)-XXV from an equilibrated 66 : 34 mixture of the trans and cis isomers [(+)-XX and (+)-XIX], which was obtained by thermal cis-trans isomerization of the cis lactam acid (+)-XIX at 190°C for 15 min. Catalytic hydrogenolysis of (+)-XXV with 10% Pd-4 and H2 gave (+)-XX in 97% yield. This made it possible to establish an alternative synthetic route to all of the I-IV-type Alangium alkaloids from ethyl cincholoiponate [(+)-XVI] , a degradation product of the Cinchona alkaloid cinchonine [(+)-V].