10-Alkenylphenothiazines. 1. Synthesis and cis,trans-isomerization of 10-propenylphenothiazines

A study was carried out on the isomerization of 10-allylphenothiazine (I) in DMSO by the action of t-BuOK, KOH and NaOH. The isomerization proceeds stereospecifically at room temperature by the action of t-BuOK at an elevated temperature by the action of KOH and NaOH to give cis-10-propenylphenothiazine (II). The effect of the t-BuOK concentration, temperature and reaction time on the isomeric composition of the 10-propenylphenothiazines formed was studied. Under conditions of kinetic control, I gives II, which isomerizes under the reaction conditions to give an equilibrium mixture of cis- and trans-10-propenyl-phenothiazine with 44-45% trans isomer III. The isomerization temperature has virtually no effect on the II/III isomer ratio.