Chemical Modification of Plant Alkaloids. 8. Stereocontrolled T-Reactions of (1 R ,5 S ,12 S )-Tetrahydrocytisine Derivatives

New heterocyclic quinolizidine systems were prepared from (1 R ,5 S ,12 S )-tetrahydrocytisine. The synthetic scheme included arylation of tetrahydrocytisine by 2-fluoro-5-nitrobenzaldehyde and condensation of the resulting aldehyde with 1,3-dimethylbarbituric acid. The Knoevenagel intermediate obtained from the condensation was cyclized by a T-reaction to give two spirocyclic products as a derivative with the lupanine skeleton and its regioisomer with the 11,15-diazapentacyclo[11.7.1.0 2,11 .0 5,10 .0 15,20 ]heneicosane skeleton. The cyclization occurred highly stereoselectively. The structures of the products were proven using NMR and X-ray crystal structure analyses.