Oxydation von Pyrrolderivaten mit Bleitetraacetat. Neuartige Porphyrinsynthesen

Syntheses and Functionalizations of Porphyrin Macrocycles

“…The required CH 2 R groups can be attached to pyrrolic intermediates by used of the Mannich reaction of pyrrole 11 with formaldehyde and dimethylamine [or with commercially available ( N,N -dimethylmethylene)ammonium iodide (Eschenmoser’s reagent [26, 27])] to give the 2-( N,N -dimethylaminomethyl)pyrrole 12 ; heating of 12 in acetic acid affords about a 50% yield of 3 (Scheme 2 ) [28, 29]. Alternatively, pyrrole 13 can be cyclotetramerized to give a similar yield of 3 by heating in acetic acid containing potassium ferricyanide [30, 31]. The Barton-Zard pyrrole synthesis [32] has afforded a very efficient access to monopyrroles of the type 14 , which can be reduced (to the carbinol 15 ) and then tetramerized under acidic conditions to give 3 in high yield [33, 34].…”

Oxidation and Reduction of the Pyrrole Ring

“…Pyrrole has not been reported to react with Pb IV compounds but the reaction of lead tetraacetate with 2-methylpyrroles in acetic acid (89) provides a convenient pathway to the correspondingly substituted 2-hydroxymethyl-and 2-formylpyrroles (see Chapter 8, Section B). No mechanism has been established for the reaction but the exclusive oxidation of α-methyl substituents suggests an intramolecular reaction of the type (B34)->(B35)-> (B36 been studied in detail but a-ethoxypyrroles, e.g.…”

Alkylpyrroles and Related Compounds

“…(Bl), which can be hydrolyzed to the corresponding carbinols, (19_20) whilst at elevated temperatures oxidation yields a-formylpyrroles to the pyrrole carboxylic acids does not occur (19) and ß-methyl groups are inert to oxidation. (B2) are converted at room temperature into a-pyrrylmethyl acetates, e.g.…”

“…Di(2-pyrryl)methanes are also obtained in good yield via the reaction oï 7V-(2-pyrrylmethyl)pyridinium salts, which are usually prepared in situ from the 2-bromomethylpyrroles, with the sodium salts of pyrrole-2-carboxylic acids, e.g. (19 · 4β · 47 · 57 · 105 -109) Although the porphin (B69) is depicted as the cyclization product, the initial reaction of the 2-pyrrylmethyl derivative may give the symmetrical dipyrrylmethane (B58) (R 1 = H), with the extrusion of a CH 2 X group, which would lead to a porphin having the "reversal" of the R 2 and R 3 groups in at least one ring. (B63), produces the 7V-ylid (B64), with which it reacts to give the l,2-di(2-pyrryl)ethene (B65) in 14% yield.…”