Porphyrins Knoevenagel reaction

Cavaleiro et al. reported the reaction of vinyl-substituted zinc porphyrins 76 with Knoevenagel products of formaldehyde 72 with several quinones 75 in refluxing 1,4-dioxane and ort/jo-dichlorobenzene (Scheme 13.22) [37]. The desired products 77 could be obtained in moderate to high yields where the exclusive formation of the para-benzoquinone is noteworthy (see also [36]). A catalytic amount of acetic acid reduces the reaction time and increases the product yield. 

---