Coumarin-Tetrapyrrolic Macrocycle Conjugates: Synthesis and Applications

Abstract

This review covers the synthesis of coumarin-porphyrin, coumarin-phthalocyanine and coumarin-corrole conjugates and their potential applications. While coumarin-phthalocyanine conjugates were obtained almost exclusively by tetramerization of coumarin-functionalized phthalonitriles, coumarin-porphyrin and coumarin-corrole conjugates were prepared by complementary approaches: (a) direct synthesis of the tetrapyrrolic macrocycle using formylcoumarins and pyrrole or (b) by functionalization of the tetrapyrrolic macrocycle. In the last approach a range of reaction types were used, namely 1,3-dipolar cycloadditions, hetero-Diels-Alder, Sonogashira, alkylation or acylation reactions. This is clearly a more versatile approach, leading to a larger diversity of conjugates and allowing the access to conjugates bearing one to up to 16 coumarin units.

Keywords: corroles; coumarins; phthalocyanines; porphyrins.

Scheme 1

Route to coumarin–porphyrin dyads [38,39].

Figure 1

Structures of coumarin conjugates obtained from natural porphyrins [43].

Scheme 2

Synthesis of aryl-substituted coumarin–porphyrin dyads [44].

Scheme 3

Synthesis of β-triazole bridged coumarin–Cu(II)porphyrin conjugates [46].

Scheme 4

Synthesis of zinc(II) β-triazolylmethyl-bridged coumarin–porphyrin dyads [47].

Scheme 5

Synthesis of zinc (II) meso-phenyl-triazole bridged coumarin–porphyrin dyads [48].

Figure 2

meso-(Coumarin-4-yl)porphyrins reported by Lin et al. [49].

Scheme 6

Route to meso-tetrakis(4-chlorocoumarin-3-yl)porphyrins reported by Amaravathi et al. [52].

Scheme 7

Route to coumarin–porphyrin conjugates reported by Fréchet and co-workers [53,54].

Scheme 8

Synthesis of three porphyrin-core dendrimers with eight coumarin units [56].

Scheme 9

Synthesis of porphyrin-core dendrimers bearing 12 coumarin units [57].

Scheme 10

A coumarin–porphyrin dyad reported by Weiying Lin and co-workers [58].

Scheme 11

Synthesis of a donor–acceptor system [60].

Scheme 12

Synthesis of supramolecular porphyrin dendrimers with coumarin units [61].

Scheme 13

Synthesis of an artificial photosynthetic reaction center [62].

Figure 3

Model compounds of artificial photosynthetic reaction centers [62].

Scheme 14

Typical route to coumarin–phthalocyanine conjugates [63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91].

Scheme 15

Synthesis of metal-free and metallophthalocyanines [64].

Scheme 16

Synthesis of coumarin–phthalocyanine conjugates 61 [92,93,94,95,96,97,98,99,100,101,102,103,104].

Scheme 17

Synthesis of coumarin–phthalocyanine conjugates [105].

Scheme 18

Synthesis of axial coumarin-substituted titanium(IV) phthalocyanines [106].

Scheme 19

Coumarin–corrole dyads obtained by the [2 + 1] approach [108].

Scheme 20

Coumarin–corrole dyad obtained under copper-free Sonogashira conditions [108].

Figure 4

Coumarin–corrole dyads obtained under copper-free Sonogashira conditions [113].

Figure 5

Coumarin–corrole dyads obtained by the [2 + 1] strategy [113].

Scheme 21

Synthesis of the dyad 82 [114].

Scheme 22

Synthesis of coumarin–corrole conjugates via hetero-Diels–Alder reactions [39].

Figure 6

Solvatochromic effect of compound 84b. Reprinted with permission from ref. [39]. Copyright © 2013 Elsevier Ltd.