Anellated pyrroles

Cycloadditions of azomethine ylides and -imines with appropriate 1,3-dipolarophiles have been employed for the preparation of anellated pyrroles and pyrazoles, respectively [49, 55-57], In analogy, phosphaalkynes have been used as 1,3-dipolarophiles for introducing a two-coordinate phosphorus leading to a variety of anellated azaphospholes. Many such examples are included in earlier reviews [17-19], In order to illustrate the synthetic strategy, two examples are cited here. 

All polycyclic pigments, with the exception of triphenylmethyl derivatives, comprise anellated aromatic and/or heteroaromatic moieties. In commercial pigments, these may range from systems such as diketopyrrolo-pyrrol derivatives, which feature two five-membered heteroaromatic fused rings (DPP pigments) to such eight-membered ring systems as flavanthrone or pyranthrone. The phthalo-cyanine skeleton with its polycylic metal complex is somewhat unique in this respect. 

Indole and carbazole, which can be regarded theoretically as derivatives of pyrrole through its anellation with one or two benzene rings, show variable behavior toward sulfenyl halides ... 

Functionalization of heterocyclic monomers with medium-length alkyl chains has provided a route to the obtainment of (at least partially) soluble polymers. To minimize interference of the functionalization with the planarity and regularity of the polymer, we have approached the problem starting from monomers constituted by two heterocycles separated by a conjugatively unsaturated spacer this can be a ring onto which the terminal heterocycles are anellated and it is intended to be the site of functionalization. In view of the merits of polypyrrole, we have focused our attention on systems (l)-(4), in which two terminal pyrrole units are... 

Apparently, benzo-anellation of pyrrol is advantageous for the long-term stability of phosphoramidites. Thus, an analog binaphthol-based hgand claimed by Du Pont [10], which was used for comparison, decomposed to an extent of approximately 20% within 10 days of storage at room temperature under argon. 

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