Porphyrins synthesis, MacDonald

MACDONALD Porphyrine Synthesis Porphyrine synthesis from dipyrrolemethanes (see 1st edition). 

Fig. 2.29 Porphyrin synthesis from dipyrrylmethanes. The MacDonald method.

The synthesis of this expanded porphyrin was successfully achieved using [66] a 2 + 3 MacDonald coupling similar to the one used to obtain sapphyrin [26, 66] and pentaphyrin [182, 183]. In this case, a diformyl bipyrrole 194 and a pyrrolyldipyrromethane dicarboxylic acid 225 were condensed in the prince of HBr to give the new macrocycle 226 (Scheme 39) [67]. Here, the requisite pyrrolydipyrromethanes were generated by HBr catalyzed condensations of... 

With the original reports of the successM synthe of the sapphyrins [26,66,152] and uranyl superphthalocyanine [112, 118, 119], interest in other expanded porphyrin systems, was kindled. The next logical step (after sapphyrin), in the expanding series of all-pyrrole systems, was the pentaphyrin macrocycle 231 which contains five pyrroles and five meso-like methine bridgra. In 1983 Gossauer et al. reported the synthesis of the first prototypical member 231 of this macrocyclic family [158, 182, 183, 185-187]. This first synthesis was achieved by a 2 + 3 MacDonald-type condensation between an oc-firee dipyrromethane 233 and a tripyrrane dialdehyde 236. More recently, the synthesis of pentaphyrin 231 has l n achieve by using a dipyrromethane 5,5 -dicarboxylic acid 235 in place of an a-firee dipyrromethane [21]. Here, as is the case in many of these kind of reactions [21,26,27,66,155], decarboxylation occurs under the reaction conditions to produce the corresponding a-free species 233 in situ. (Scheme 40) [21]. 

The first synthesis of pentaphyrin was reported by Gossauer in 1983. He used an HBr-catalyzed 2 + 3 MacDonald-type condensation between the diformyl tripyrrane 6.29 and the a-free dipyrrylmethane derivative 6.32 to establish the basic macrocyclic framework. Oxidation with chloranil then gave pentaphyrin 6.35 in 31% overall yield (Scheme 6.4.1). Subsequent to this original disclosure, syntheses of pentaphyrins with various other peripheral substituents appeared in the literature (e.g., 6.38 and 6.39). They were all made using this same general procedure." Interestingly, it was found that pentaphyrins could not be prepared when the nucleophilic and electrophilic nature of the reactant dipyrrylmethane and tripyrrane (the 2 and 3 components, respectively) were reversed. This became evident when the diacid tripyrrane 6.38 and the diformyl dipyrrylmethane 6.39 were reacted under conditions identical to those used to prepare pentaphyrin 6.35. Here, only porphyrins, and not pentaphyrins, were obtained (Scheme 6.4.2). " ... 

Using an approach similar to that described in the preceding paragraph, this methodology enables the synthesis of 5,15-diaryl- or 5,15-dialkyl-porphyrins from a dipyrromethane and an alkyl- or arylaldehyde linker molecule.36 In the example shown, porphyrin (73) can be obtained from the 5-mesityldipyrromethane (74) (prepared in a manner similar to that described for (64)) and 4-iodobenzaldehyde if the dipyrromethane (74) had been unsubstituted at the 5-position, a 5,15-diarylporphyrin would have resulted (Scheme 22). Mixed 5-alkyl-15-arylporphyrins, such as (75), can be prepared35,46 by treatment of 1,9-di-unsubstituted 5-alkyldipyrromethanes (e.g., (76)) with l,9-diformyl-5-aryldipyrromethanes (77) in a MacDonald-type [2 + 2] approach (Scheme 23). 

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