Terpyrrole

The isosmaragdyrins have been prepared1 -14 by a McDonald-type strategy. On acid-catalyzed condensation between an a-unsubstituted terpyrrole 3713 and a dipy rrylmethanedicarbaldehyde 43 the macrocycle 44 is formed directly without the requirement of an oxidation step. In the primarily formed diprotonated form of isosmaragdyrin 44, the cyclic conjugation is disrupted. 

Sessler and coworkers have synthesized [22]pentaphyrin(2.1.0.0.1) 151 (Scheme 61) by condensing terpyrrole 146 with an alkyne bridged bipyrrole 149 under MacDonald conditions giving rise to a 22jt aromatic macrocycle dehydropentaphyrin 150, which upon treatment with a poisoned Lindlar catalyst (Pd/CaC03) gave 151 (1995TL4713). 

The smallest pentapyrrolic is [20]pentaphyrin(1.0.1.0.0) (orangarin) 152. Acid-catalyzed condensation between hexamethyl terpyrrole 146 (Scheme 62) and diformyl bipyrrole 124 (1995CEJ56) furnishes 152. Compared to Huckel (18jt, 22it) aromatic species, 152 is 20jt antiaromatic as attested by its extremely broad absorption spectrum. While the pentapyrrolic aromatic species displays appreciable fluorescence, no appreciable fluorescence is seen for the antiaromatic species. 

Sessler et al. (1994ACI1509) made decapyrrolic turcasarin 186 (Scheme 77) by acid-catalyzed condensation of dialkylterpyrrole 184 and hexamethyl-terpyrrole 185 (R1=Et), following "3+2+3+2" condensation. 

Starting from the mid-1930s, the template syntheses of porphyrines and cor-rines have been developed [318], which are widely applied at present to isolate metal complexes of these terpyrrol and terpyrrolidine systems. Examples of these reactions are the transformations (3.155) ... 

Direct iodination of pyrrole 358 with Nal and I2 (H2O, reflux, 3 h) gave the 5-iodopyrrole 359 in excellent yield (Scheme 81) <2004T11283>. This compound was involved in the synthesis of a new terpyrrolic analog of DPQ (dipyrrolylquinoxaline) 360. 

Silver enolates are proposed as reactive intermediates in the reaction of sUyl enolates with AgaO in dmso. An important feature of the reaction is the regiospecific formation of l,4-diketones °j. Sessler and coworkers reported that the key step in the preparation of / -substituted tetra- and hexaalkylterpyrrols is the copper(II) triflate-mediated oxidative coupling of the Ida-derived enolates of a-keto pyrrols. The coupling reaction shown in equation 24 produces a mixture of distereoisomers which does not require separation and can be directly converted to the corresponding terpyrroles. 

The smallest pentapyrrolic expanded porphyrin to be reported to date is the so-called orangarin macrocycle (alternatively referred to as [20]pentaphyrin-(2.1.0.0.1) ). It was prepared in the form of the decaalkyl-substituted system 6.9 via an HCl-catalyzed condensation between the a-free terpyrrole 6.7 and the diformyl... 

An alternative synthesis of this type of molecule was also attempted. This approach, shown in Scheme 6.2.2, involved reversing the nucleophilic and electrophilic building blocks relative to those shown in Scheme 6.2.1. Thus, the diformyl terpyrrole 6.12 was condensed with the dicarboxyl-substituted dipyrrylmethane 6.13. 

A single crystal X-ray structural analysis of the alkyne-containing product 6.26a revealed that the macrocycle adopts a near-planar conformation in the solid state (Figure 6.3.3). Deviation from planarity results, presumably, from the methyl-methyl steric interactions within the terpyrrolic subunit. The crystallographic data also served to support the contention that the macrocycle does indeed contain a true an alkyne-like (C-C=C-C) fragment. Such a bond isolation, although expected in the present instance, stands in contrast to what is seen in the case of Vogel s stretched porphycene precursor. In this latter instance cumulene-type (C = C = C = C) bond delocalization is observed. 

Figure 3. Schematic of conductive terpyrrole units connected via degradable ester linkages and flexible aliphatic chains.

Terpyrroles with methyl esters groups at their a positions will be synthesized, using modified procedures of Wallace et al. (23) and Merrill and LeGoff (24). 

The methyl esters of the terpyrrole will be hydrolyzed to form diacids. 

Figure 5. (a) Structure of new terpyrrole derivative with thiophene unit. (b) Final predicted structure of biodegradable polypyrrole erivative. 

Currendy, the hydroxy-terminated terpyrrole derivative (as shown in Figure 5a) has be successfidly syndiesized and characterized using NMR ( H and C) and mass spectroscopy. Figure 6 shows die proton NMR of the terpyrrole derivative diat is depicted in Figure 5a The peak located farthest downfield... 

Figure 6. Proton H) NMR for terpyrrole derivative in Figure 5a. NMR obtained using a Varian Ultra Plus (300MHz).

Terpyrroles. POGI3 added with stirring at 0° under Ng during 0.5 hr. to a mixture of 5-methoxycarbonyl-2,2 -bipyrrole, methyl pyroglutamate, di-... 

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