Effect of Reaction Media on Photosensitized [2+2]- Cycloaddition of Cinnamates
Fecha
2020Resumen
The outcome of photosensitized [2+2]-cycloaddition reactions
of various cinnamates has been compared in different reaction
media, including homogeneous organic solutions under inert
conditions, degassed water, and aerated physical gels. The
reactions were performed under LED blue light (λmax=455 nm)
irradiation and [Ir{dF(CF3)ppy}2(dtb-bpy)]PF6 (1.0 mol%) as photocatalyst.
The processes were optimized taking into consideration
solvent, gelator, and substrate. Comparative kinetics
analyses, as well as the effect of the reaction media on the
diastereoselectivity of the process, were evaluated during this
investigation. In a number of cases, carrying out the reaction in
a less polar solvent, like toluene or highly polar solvent, like
water had a tremendous impact on the diastereoselectivity of
the process, pointing towards an effect on the stabilization of
the putative diradical intermediate in this medium. Moreover,
while for reactions run in homogeneous solution oxygen needs
to be excluded, no erosion in yield is observed when the
photoadditions were run in aerated gel media.