Iodination of Cytisine and Methylcytisine Alkaloids

Iodination of the 2-pyridone core of (–)-cytisine and methylcytisine by one equivalent of ICl or N-iodosuccinimide (NIS) in acidic solution gave primarily the 9-iodo derivatives although the starting alkaloid was incompletely converted. Use of an excess of the reagents under the same conditions gave 9,11-diiodo derivatives in 72 and 76% yields. 9-Iodomethylcytisine was prepared (61% yield in two steps) by treatment of methylcytisine with an excess of NIS in trifluoroacetic acid followed by deiodination of the 9,11-diiodo derivative by Zn dust in a mixture of EtOH and aqueous HCl.