Encouraged by the above trans-cis isomerization of azo enediynes in effecting a change in BC kinetics, a novel cyclic bispropargyl sulfone A containing stable E -azo moiety has also been synthesized by Basak et al. (Scheme 101).
Scheme 101. Synthesis of azo bispropargyl sulfones. |
The compound A upon irradiation with long UV (350 nm) isomerized to the Z compounds B, which can be thermally re-isomerized to the E compounds. The E isomer A upon treatment with Et3N equilibrates to the mono-allenic sulfone C . The formation of bisallene E was not seen during the base treatment. On the other hand, a similar treatment of the corresponding Z isomer forms the monoallene D first, which subsequently further isomerized to the unstable bisallene F which finally underwent decomposition presumably via the Garratt−Braverman pathway (Scheme 102). Incubation with plasmid DNA also indicated higher DNA-cleavage efficiency ( ~2.5 times) for the Z isomer.
Scheme 102. Photochemical trans-cis isomerization of azo bis-propargyl sulphones their reactivity thereof. |
