Porphycene expanded

Heteroporphyrins Core modification Tetrathiaannulenes Porphycenes Porphyrinoids Expanded porphyrinoids. 

The general synthetic approaches for expanded porphycenes rely upon the insertion of alkylidene or alkylidyne moieties either as the meso-bridge or between the 2 and 2 positions of the bipyrrole subunits. Thus, the vinylogous dialdehyde 72 (Scheme 35) obtained from 4,4 -dipropyl-2,2 -bipyrrole with 3-(dimethyl-l-amino)acrolein has been converted to (1993PAC143) to 73 using a standard McMurry-type coupling. Expanded porphycene 73 with TFA precipitates as dication 74. 

Scheme 35 Synthesis of expanded porphycene using vinylogous dialdehyde.

Similarly, the monovinylogous diformyl bipyrrole 75 (Scheme 36), under reductive McMurry conditions, followed by air oxidation, results in the formation of expanded porphycene 77 as the dominant product (7%)... 

Expanded porphycene 80 containing triple bonds inserted between the 2 and 2 positions of the 2,2 -biyrrole subunits (1990ACI1385,1990ACI1387) is a 22it-electron aromatic macrocycle that displayed an acetylene-cumulene bonding motif, a feature in common with Sondheimer-Nakagawa [4n+2]dehydroannulenes. 

We have compiled synthetic chemistry and properties of porphyrin analogues containing only furan, imidazole, or thiophene subunits in place of pyrrole subunit(s). Expanded porphyrinoids have been excluded. This write-up is not intended to give a comprehensive treatment, but is aimed to complement earlier reviews (06CCR468, 08CSR215). In the following two sections, the chemistry of core-modified porphycenes and porphyrins is presented. 

A new series of bisvinylogous porphycene compounds have been reported by Vogel and co-workers [199]. These compounds are extended forms of porphycene, an isomer of porphine [4, 200]. The self-condensation of the bis-pyrroleacetylene derivative 298 was used to obtain the expanded porphyrin 300, presumably via the intermediate 299 (Scheme 57). The NMR spectrum of 300... 

Synthesis and characterization of other related macrocycles, including chlorins, " isobacteriochlorins, bacteriochlorins, mono- and dioxoporphyrins, " other more highly saturated hydroporphyrins, N-alkyl- or A-arylporphyrins, some of which are chiral, porphodimethenes, thiaporphyrins, " oxaporphyrins, N-confused " and carbapor-phyrins, porphycenes " and corrphycenes, " tetraazaporphyrins, phthalocyanines, the ring-expanded sapphyrins, texaphyrins and others, and the ring-contracted corroles " and corrolazines have also been synthesized and are discussed in the indicated references. 

Vinylogous porphyrins are formally built up of odd-numbered carbon spacers separating four pyrrole rings. There are, however, several expanded porphyrins that contain four pyrrolic or pyrrole-like subunits that contain only even-numbered carbon spacers. These macrocycles will be grouped under the general heading stretched porphycenes , since they are typically prepared via the low-valent titanium mediated coupling of pyrrolic aldehydes just as are the porphycenes (cf. Chapter 3). 

A reductive McMurry-type approach similar to that used for the synthesis of porphycenes (Chapter 3) and ozaphyrins (Chapter 6) has also been applied to the synthesis of hexapyrrolic macrocycles. This approach has been explored independently by Johnson and Ibers Cava and Merz and Neidlein " and has led to a range of hexaphyrin-(2.0.0.2.0.0)-type expanded porphyrins (e.g. 7.55) that are gen-erically known as homoporphycenes or bronzaphyrins. As is often the case, the trivial name bronzaphyrin, originally coined by Johnson and Ibers ° reflects the color of the macrocycle observed in organic media. Indeed, in solution, these macro-cycles typically exhibit a distinctive bronze color. For the purpose of continuity in this chapter, the name bronzaphyrin will be universally employed for all macrocycles of the hexaphyrin-(2.0.0.2.0.0) type. 

Much less is currently known about the actual in vivo photosensitizing capabilities of other expanded porphyrins. In fact, only the expanded porphycene 10.5 (lowest energy = 795 log e = 4.78 in benzene ) appears to... 

Porphyrin has fourfold symmetry, with the pyrrole rings connected by alternate meso bridges. About eight isomers can be sketched down by changing the sequence of the subunits, of which porphycene (37), hemiporphycene, corrphycene, and isoporphycene have been synthesized to date. Expanded porphyrins are, by definition, those possessing more than 16 atoms in the smallest circuit of the macrocycle. Sapphyrin (39) is the common expanded porphyrin derived by the insertion of an additional pyrrole ring into the macrocycle [40]. 

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