Synthesis and reactivity of azobenzene-based bispropargyl sulfones: interesting comparison between cyclic and acyclic systems

Azobenzene-based bispropargyl bissulfone 3 containing stable E-azo moiety has been synthesized. Upon irradiation with long wavelength UV it isomerized to the Z-form 4, which can be thermally reisomerized to the E-isomer. Reactivity towards isomerization to the allenic system as well as DNA-cleaving efficiency under basic conditions was found to be significantly lower as compared to the previously synthesized cyclic sulfones 1 and 2. This lowering of reactivity can be explained in terms of low conversion to the allenic form and hence the lower extent of alkylation of DNA-bases, the only possible DNA-cleavage pathway for 3 and 4.