Meso -Functionalized dipyrromethanes

In 2007, Singh and coworkers developed lithiation-substitution methodology for meso-functionalized dipyrromethanes 257 (Scheme 100) (07TL227), free from all limitations. 

In 2011, Singh et al. have reported the synthesis of meso-functionalized dipyrromethanes (11SC3491) 261 (X = NH) (Scheme 101) as well as unsym-metrical bis(heterocyclyl)methanes through Grignard addition of various aliphatic and aromatic halides on pyrrole-2-carboxaldehyde, followed by BF3 OEt2-catalyzed condensation of pyrrole-2-carbinols with pyrrole, etc. 

Scheme 101 Synthesis of meso-functionalized dipyrromethane through Grignard addition.

Alternative approaches for substituted porphyrins have been devised in which pre-functionalized dipyrromethane derivatives 3 are condensed with similar diformyl dipyrromethanes 4 through a "2+2" condensation to form meso-tetraarylporphyrins 5 (Scheme 3). Such condensations are usually catalyzed by acids and the intermediate porphyrinogens are oxidized by air to obtain porphyrins. In a similar "3+1" synthetic approach, tripyrranes 6 are condensed with 2,5-diformylpyrroles to form etioporphyrin 5 (1996CEJ1197). 

A simple and versatile one-pot synthesis of meso-substituted trans-A2B-corroles (Scheme 7) was reported by Gryko and Jadach (01JOC4267). It affords regioisomerically pure frans-A2B-corroles 11 through the TFA-catalyzed condensation of a dipyrromethane 10 and an aldehyde followed by oxidation with DDQ. The synthesis is compatible with diverse functionalities ester, nitrile, ether, fluoro, hydroxy, etc. on the aryl group of the... 

A heteroporphyrin containing two functional groups, trans 21-oxa 234a and 21-thiaporphyrins 234b (Scheme 92), have been obtained from 233 and a meso-ary 1-substituted dipyrromethane (1999JOC7890). 

A variation of this method that removes the water produced in the pyrrole/aldehyde or hydrated aldehyde condensation has been used to produce meso-tetrakis(perfluoroalkyl)porphyrins. Lindsey s laboratory has also reported a rational synthesis of weyo-substituted porphyrins bearing one nitrogen heterocyclic group that can readily be used for preparing other mono-functionalized porphyrins, methods for minimi zing scrambling in the synthesisof tran -porphyrins from dipyrromethanes and aldehydes, and a rational synthesis of porphyrins bearing up to four different meso substituents. ... 

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