Several chemical transformations were carried out with ajmalicine (1), a heteroyohimbine alkaloid, with a view to studying the reactivity of the enolic ester system occurring in the heterocyclic ring. Ajmalicine hemiacetal (2) and ajmalicine 17-methyl acetal (6) were prepared by treating 1 with aqueous and methanolic sulfuric acid, respectively. C-17 epimerization of 6 was observed in polar aprotic solvents, but this isomerization in 2 was prevented due to hydrogen bonding between vicinal carbomethoxy and hydroxy groups. Ajmalicial (12), the aldehydic derivative of 1, was prepared by following a new one-step pathway. Both cyclic (12) and open (14) forms of ajmalicial, a hemiacetal, were isolated and characterized. The cyclic form (12) was found to exist in an all-chair conformation (11). But for the open form (14) the most stable conformation (15) demands that the D ring must ooccur in a twist-boat form. This spatial orientation facilitated an electrophilic attack by the C-16 aldehyde group at C-7. The product was shown to be a new isomer (16) of ajmalicial having a 5,16-secoajmaline skeleton. The preferred conformation of 16 is 17. This new isomer was susceptible to protic solvents. LAH reduction of 1 afforded ajmalicinol (23). The structures and conformations of all these products could be established from spectral analyses including 13C NMR spectra. © 1982, American Chemical Society. All rights reserved.