Conjugated macrocycles

The first example of successful diene-diene RCM to construct a macrocyclic conjugated triene was disclosed by Wang and Porco in the first total synthesis of oximidine II (258) [121]. Oximidine II belongs to the family of salicylate en-... 

The first example of successful diene-diene RCM to construct a macrocyclic conjugated triene, was disclosed... 

The beautiful colors associated with porphyrin and chlorophyll systems are manifest in their characteristic electronic absorption spectra. The most intense band in the spectra, around 400 nm, is known as the Soret band it is intrinsic to the large macrocyclic conjugated pathway and has molar extinction coefficients usually between 150 000-400 000. This extinction value is lower in chlorins than in porphyrins, and the band is absent in porphyrinogens (6) and ring-opened bile pigments. 

Type C with a, b, c even represents combined local and macrocyclic conjugation. Three annulenoid pathways coexist, one for each pair of branches. 

These three conjugation types may correspond to aromaticity or antiaromaticity, in accordance with the Hiickel rule. They can be depicted using the partial resonance structures given in Fig. 4. An additional requirement is that each branch required to participate in cyclic conjugation not contain a formally two-electron heteroatom site (such as -NH-, -O-, etc.) or exocyclic double bonds (such as carbonyl groups). These structural elements are incompatible with Kekule-type canonical structures. Finally, it should be noted that in the case of type C structures macrocyclic conjugation will be preserved, even when one of the a and b branches is not fully conjugated. 

A number of N-confused systems are known with macrocyclic conjugation interrupted by sp3 meso bridges. These systems, which include analogs of calixpyrroles [252] and calixphyrins [253], fall outside the scope of the present review. A number of fully conjugated N-confused expanded porphyrins have been obtained by use of predesigned N-confused substrates. The most representative examples of such structures are collected in Fig. 32. 

Considerable interest has been focused on the physico-chemical properties of sandwich complexes of lanthanide(III) ions with two macrocyclic conjugated rings such as phtalocyanine. Several X-ray crystallographic studies on Nd(III) (Kasuga et al., 1980) and Lu(III) (Mous-... 

In the case of an approach toward cytotrienins, Panek and coworkers achieved different chemoselectivity according to the catalyst they employed [22]. They first tried RCM of polyene 21 with catalyst G2 (Scheme 2.9). Unexpectedly, only the macrocyclic conjugated diene 22 is obtained presumably, initiation of the metathesis reaction occurs at the internal bond of one of the dienes. On the other hand, use of catalyst G1 leads to the expected conjugated triene 23 in 73% yield. 

The typical reactions of the porphyrin ligand can be compared to those of aromatic compounds, whereas interruption of the macrocyclic conjugation path at one methine bridge leads to a more polyene-type reactivity pattern of the resulting phlorins. 

Although only two cycloarenes (coronoid hydrocarbons) have been synthesized so far, many other macrocyclic conjugated hydrocarbons are known chemically, and they keep attracting constant interest in organic chemistry. 

Phthalocyanine compounds contain macrocyclic conjugated pi-electron systems and metal ions in the central void. These phthalocyanine structures are very similar to porphyrins, one of the most important compounds in biochemistry. Accordingly, phthalocyanine compounds are expected to facilitate interesting catalysis and multielectron processes. Almost all metal and semi-metal ions can be incorporated in the central void of the phthalocyanine molecule, and the characteristics of such phthalocyanine compounds can be modified by the metal ions. About seventy metals are known to incorporate in the phthalocyanine molecule. 

Jefferson E, Swayze E, Osgood S, Miyaji A, Risen L, Blyn L (2(X)3) Antibacterial activity of quinolone-macrocycle conjugates. Bioorg Med Chem Lett 13 1635-1638... 

As Aihara points out, This approach is general and applicable to any macrocyclic conjugated systems with an inner cavity Thus, the myth of super-aromaticity, just as has been the case with the myth of parity, has been demoted if not ended. 

---