Pyrrole bonding

Condensed Pyrroles. Pyrroles can be condensed to compounds containing two, three, or four pyrrole nuclei. These are important ia synthetic routes to the tetrapyrroHc porphyrins, corroles, and bile pigments and to the tripyrroHc prodigiosias. The pyrrole nuclei are joiaed by either a one-carbon fragment or direct pyrrole—pyrrole bond. 

N-methylpyrrolidine gave a small amount (5%) of unchlorinated compound 215 with the pentathiepin ring fused across the 2,3-pyrrole bond and N-ethylpyrro-lidine gave a higher percentage (23%) of product 216 fused similarly to the former but chlorinated in the free a-position of the pyrrole (Scheme 113). 

A general feature of weso-phenyl substituted Co3 + corrolates is then that the planarity of the macrocyclic ligand is maintained in solution the pattern shown by the resonances due to the peripheral methyl groups in fact are indicative of the existence of a C2 symmetry axis the direct pyrrole-pyrrole bond typical of a planar corrole skeleton, confirmed also by the signals due to the meso-protons, if present. 

As compound 144 may only exist in the (aR,20R) relative configuration, the quantitative conversion of amino-acid 143 to 144 indicates that free rotation around the phenyl-pyrrole bond occurs in 143... 

If the pyrrole C(1 (-positions are chlorinated, the pentathiepane ring is fused across the 3,4-pyrrole bond to give pentathiepinopyrroles of type 819 (Cl for Me) in high yield <2005OBC3496>. 

Figure S.S Structure of pyrrole (bond lengths in pm, bond angles in degrees).

For the first time, the reaction of ketoximes with acetylene has been applied for the preparation of pyrroles bonded with the thiophene ring in the work [244], which describes synthesis of 2-(2-thienyl)pyirole (in 60% yield) from 2-acetylthio-phene (via its oxime) in the system KOH/DMSO (100°C-140°C). In the presence of acetylene excess under the same conditions, 2-(2-thienyl)-N-vinylpyrroles (50% yield) is formed. 

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