Bipyrrole diformyl

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%)... 

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. 

The first [26]hexaphyrin(1.1.0.1.1.0) 154 (Scheme 63) was obtained by condensing tetrapyrrolic precursor 153 with the diformyl bipyrrole 124 under acid-catalyzed conditions, followed by air oxidation. The resulting macrocycle was assigned the trivial name "rubyrin" due to its dark orange-red color in DCM (1991ACI977). 

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... 

A more direct, 2 + 2 approach to the synthesis of cobalt(III) corroles has been described. It involves condensing a diformyl bipyrrole such as 2.140 with a diacid dipyrrylmethane such as 2.36. This approach is thus similar to the one used to obtain the bifuran-containing corroles 2.3 2.40 described earlier. In the present instance, the diacid bipyrrole 2,141 may also be reacted with a diformyl dipyrrylmethane such as 2.142. This affords corrole 2.125b (Scheme 2.1.37). In either case, the reaction must be carried out in the presence of Co(II) and PPhs. This requirement for a presumably coordinating metal cation is in stark contrast to what is seen in the case of the bifuran analog there, no metal is needed to template the reaction. ... 

Vogel, et al. have recently reinvestigated the acid-catalyzed condensation between diformyl bipyrrole and dipyrrylmethane, in the absence of a metal cation. Interestingly, these researchers reported the isolation of cyclic octapyrroles from these reactions.For a complete discussion of this and other related findings, see Chapter 8. 

When subjected to catalytic hydrogenation with 10% Pd/C in ethyl acetate, porphycene 3.2 was found to be reduced to the 2,3-dihydroporphycene 3.90. Interestingly, this same 2,3-dihydroporphycene 3.90 was also obtained as a side-product (ca. 1 % yield) when the reductive carbonyl coupling of diformyl bipyrrole... 

A potentially practical synthesis of weTO-diarylsapphyrins has recently been introduced by Sessler and Kodadek. It involves the one-pot condensation reaction between diformyl bipyrrole 5.10, pyrrole 5.29, and benzaldehyde 5.30 using BF3 MeOH as the Lewis acid catalyst. In this 2 -I- 1 + I + 1 approach, careful control of the ratio of starting materials is required. When run properly, however, this one-step procedure allows for the preparation of 10,15-diphenylsapphyrin 5.33 in ca. 10% yield (Scheme 5.2.1). In a similar fashion, the P-CH3- and p-CN-deriva-tives 5.34 and 5.35 were prepared using the appropriately substituted benzaldehyde... 

In order to confirm the structure of the heterosapphyrins that were presumed to have formed during the course of the above reactions, Johnson and coworkers carried out a 3 + 2 reaction analogous to that now commonly used to prepare pentaazasapphyrins (vide supra). Here, it was found that reacting diformylbifuran 5.51 with the dicarboxyl-substituted tripyrrane 5.58 did indeed produce the hexaalkyl sapphyrin derivative 5.60 (Scheme 5.3.2). Johnson, et al. also used this approach to prepare the thiasapphyrin analog 5,61. This sapphyrin was obtained in 19.5% yield from diformyl bipyrrole 5.9 and the dipyrrolylthiophene 5.59. 

In later work, Grigg and Johnson reported on their efforts to synthesize pentaazanorsapphyrins 5.148-5.151. This they attempted via the acid-catalyzed condensation of the diformyl bipyrrole derivatives 5.143 and 5.9 with the pyrrolylbipyr-roles 5.144 and 5.145." While UV-vis spectroscopic analyses of the crude reaction mixtures revealed sharp absorption maxima at ca. 450 nm (and could thus be interpreted in terms of the desired pentaaza systems having been formed), these putative norsapphyrins proved too unstable to isolate. Thus, they could never be fully characterized nor could the success of this reaction sequence ever be confirmed. 

The synthesis of rubyrin 7.25 involves an acid-catalyzed 4 + 2 MacDonald-type condensation between the diformyl bipyrrole 7.21 and the diacid tetrapyrrane 7.23 (Scheme 7.2.1). After oxidation and purification, a roughly 20% yield of a blue crystalline solid is obtained, which, on the basis of solution-phase spectroscopic and solid-state structural studies vide infra), was assigned the hexapyrrolic structure 7.25. Using a similar procedure, rubyrins 7.26 and 7.27 were also prepared. While the first of these (like 7.25) proved stable, rubyrin 7.27 was found to decompose during chromatographic purification. It was thus characterized only by UV-vis spectroscopy and mass spectrometry. ... 

An alternative synthesis of these mono-phenyl-substituted rosarinogens was also developed by Sessler and his group. In this instance, the phenyl-substituted tetrapyrrane derivative 7.50 was reacted with the diformyl bipyrrole 7.21. While this approach afforded the rosarinogen macrocycle 7.49 in only moderate yield, an advantage of this method is that it is potentially amenable to heteroatom substitution (Scheme 7.4.3). Indeed, it has already been found that using the diformyl bifuran 7.51 in place of the diformyl bipyrrole 7.21 affords the dioxarosarinogen 7.52. ... 

The final cyclooctapyrrole reported by Vogel and coworkers is the 32 n-electron (therefore, formally non-aromatic) octaphyrin-(l.O.l.O.l.O.l.O) derivative 8.20." This macrocycle was first synthesized in 7% yield as the result of a [1 + 1] acid-catalyzed condensation between the linear tetrapyrroles 8.18 and 8.19. Subsequently, this same macrocycle was synthesized from bipyrrole 8.21 and diformyl bipyrrole 8.10 in higher yield (11%) than originally obtained via the [1 + 1] approach (Scheme 8.2.3). This finding attests to the generality of the [2 + 2] strategy certainly, it appears to be a good synthetic route to cyclic octapyrroles. 

A final example of a bipyrrole-derived [2 + 2] Schiff base expanded porphyrin was reported by Johnson, et al. in 1995 in the form of a preliminary abstract. In this instance, macrocycle 9.34 was prepared via the condensation of hydrazine with the diformyl bipyrrole 9.23 (Scheme 9.1.6). This macrocycle was reported to exhibit spectral characteristics indicating that it is antiaromatic. Further, treatment with manganese dioxide was said to result in oxidation of 9.34 to an aromatic 22 7t-electron system. This latter system proved, however, to be much less stable than its 24 7i-electron parent , and this precluded isolation and characterization. In fact, with full experimental details not yet reported in the literature, the characterization, and structural assignment for 9.34 must also be considered tentative. 

Another improved synthesis of unsubstituted porphycene 38 (R=H) using ferf-butyl substituents as temporary stabilizing groups, as outlined in Scheme 22, has been described (07JPP596). Thus, deprotection of the N-tosyl-protected bipyrrole 46, followed by formylation yields diformyl intermediate 36, which readily undergoes McMurry coupling to produce 38 (R=H, f-Bu). 

An asymmetrical porphycene (07JPP596) bearing only two methyl groups at w/cso-positions was synthesized via the cross-coupling of diformyl 36 (R=f-Bu) and diacetyl bipyrroles 53 (R=Me), followed by facile oxidation to give 55 (Scheme 27). 

Another structural variant of the original porphycene skeleton was recently mentioned in the context of a personal review by Vogel. This is the fused benzo-porphycene derivative 3.42, a species that is obtained from the reductive carbonyl coupling of the diformyl P-fused bipyrrole 3.40 (Scheme 3.1.5). Like the 9,10,19,20-substituted porphycenes, the intermediate dihydroporphycene obtained in this... 

In the full paper describing Woodward s sapphyrin-directed studies, it was noted that small amounts of sapphyrins could also be prepared via the HBr-catalyzed reaction between a bipyrrole dicarboxaldehyde and a dipyrrylmethane dicarboxylic acid. Additionally, the HBr-catalyzed reaction of 3,4-dimethylpyrrole 5.5 with 2,5-diformyl-3,4-dimethylpyrrole 5.3 was reported to afford small yields of decamethyl-sapphyrin 5.6 (Scheme 5.1.3). The fact that any sapphyrin could be isolated from these reactions, or even from the procedures of Schemes 5.1.1 and 5.1.2, attests to the stability of this pentapyrrolic macrocycle. 

It is worth mentioning that an alternative 3 + 2 synthetic approach to sapphyrin has been reported. Specifically, it was found that the alkyl-substituted sapphyrin 5.19 could be prepared via the acid-catalyzed condensation of pyrrolyl-bipyrrole 5.27 with diformyl dipyrrylmethane 5.28 (Scheme 5.1.5). Following oxidation with air and chromatographic purification, this method affords a 35% yield of the desired sapphyrin. Unfortunately, this method has yet to find any kind of general applicability. This is most likely a reflection of the fact that the needed pyrrolyl-bipyrrolic precursors are hard to make. 

Prior to developing the above synthesis, Sessler and coworkers discovered a different route to meso-axy sapphyrins. This synthetic strategy, like so many in the area of sapphyrin-related research, is based upon a reaction that was not initially intended to produce sapphyrins. Specifically, it involves the reaction between bis(pyrrolyl)bipyrrole 5,38 and diformyl dipyrrylmethane 5.39, and was found to produce, quite unexpectedly, sapphyrin 5,41 in ca. 5% yield, with none of the intended hexapyrrolic macrocycle 5,40 being detected (Scheme 5.2.3). It was thus considered that such a 4 + 2 = 5 approach might prove useful for the synthesis of we o-phenyl sapphyrins. This indeed proved to be the case. In fact, this strategy has... 

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