New synthesis of benzo [a]quinolizidin-2-ones via protected 2-aryl-4-piperidones

A new synthesis of 9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-benzo aquinolizin-2-one ( 1a and its 3-ethyl derivative 1b via the corresponding 2-(3,4-dimethoxyphenyl)-4-piperidone ethylene acetals 7 is reported. Alkylation of 2-arylpipendires 7 with 2-bromoethanol followed by oxidation of the resulting amino alcohols 9 with oxalyl chloride and dimethyl sulfoxide afforded the aldehydes 10 , which were cyclized with hydrochloric acid to give 7-hydroxybenzo[α]quinolizidines 11 . The reduction of 1 with trinethylsilane and subsequent acid hydrolysis led to benzo aquinolizidin-2-ones 1 .