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Issue 5, 2001
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Investigation of porphyrin-forming reactions. Part 1. Pyrrole + aldehyde oligomerization in two-step, one-flask syntheses of meso-substituted porphyrins

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Abstract

A deep understanding of the two-step, one-flask synthesis of meso-substituted porphyrins requires characterization of the acyclic oligomers, which typically constitute ≥50% of the products. We have employed laser desorption mass spectrometry (LD-MS) to obtain a qualitative yet high resolution view of the oligomer content of crude oxidized reaction mixtures. This methodology complements other analytical methods which provide information regarding yields of porphyrin, other macrocyclic products, and unreacted aldehyde. Our findings include the following. (1) Crude oxidized porphyrin reaction mixtures provided peaks in the LD-MS spectrum which were readily assigned to oligomers (m/z 100–2000) derived from pyrrolealdehyde condensation. The oligomers comprised one of four series depending on the ratio of pyrrole and aldehyde units. (2) Quite disparate reaction conditions that gave good yields of porphyrin also afforded a similar oligomer composition. (3) The change in the nature of the oligomers over time was readily monitored. (4) The maximum yield of porphyrin and the maximum diversity of the oligomer composition were attained at similar times. (5) The decline in yield of porphyrin at long reaction time was accompanied by truncation, not elongation, of oligomers. (6) The onset of the truncation of oligomers and the decline in yield of porphyrin were accompanied by a decrease of the aldehyde to low levels. (7) Pyrrole was incorporated into the growing oligomers more rapidly than aldehyde. Taken together, these studies show how various conditions alter the course of the pyrrolealdehyde condensation.

Graphical abstract: Investigation of porphyrin-forming reactions. Part 1. Pyrrole + aldehyde oligomerization in two-step, one-flask syntheses of meso-substituted porphyrins [ ]

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Publication details

The article was received on 13 Nov 2000, accepted on 14 Mar 2001 and first published on 20 Apr 2001


Article type: Paper
DOI: 10.1039/B009088N
Citation: J. Chem. Soc., Perkin Trans. 2, 2001, 677-686
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    Investigation of porphyrin-forming reactions. Part 1. Pyrrole + aldehyde oligomerization in two-step, one-flask syntheses of meso-substituted porphyrins

    G. R. Geier III and J. S. Lindsey, J. Chem. Soc., Perkin Trans. 2, 2001, 677
    DOI: 10.1039/B009088N

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