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  • Synthesis of indenoporphyrins, highly modified porphyrins with reduced diatropic characteristics.

Synthesis of indenoporphyrins, highly modified porphyrins with reduced diatropic characteristics.

The Journal of organic chemistry (2011-05-24)
Timothy D Lash, Breland E Smith, Michael J Melquist, Bradley A Godfrey
ABSTRACT

Indene-fused porphyrins have been synthesized starting from 2-indanone. Knorr-type reaction of oximes derived from benzyl or tert-butyl acetoacetate with 2-indanone and zinc dust in propionic acid gave good yields of indenopyrroles. Treatment with N-chlorosuccinimide then gave 8-chloro derivatives, and these reacted with 5-unsubstituted pyrroles to give dipyrroles incorporating the fused indene unit. Hydrogenolysis of the benzyl ester protective groups afforded the related dicarboxylic acids, but condensation with a dipyrrylmethane dialdehyde under MacDonald "2 + 2" reaction conditions gave poor yields of the targeted indenoporphyrins. However, when an indene-fused dipyrrole was converted into the corresponding dialdehyde with TFA-trimethyl orthoformate and then reacted with a dipyrrylmethane dicarboxylic acid, an indenoporphyrin was isolated in 26% yield. The porphyrin gave a highly modified UV-vis absorption spectrum with three strong bands showing up in the Soret region and a series of Q bands that extended beyond 700 nm. The proton NMR spectrum also showed a significantly reduced diamagnetic ring current where the meso-protons gave resonances near 9.3 ppm instead of typical porphyrin values of 10 ppm. Nickel(II), copper(II), and zinc complexes were also prepared, and these exhibited unusual UV-vis absorption spectra with bathochromically shifted Soret and Q absorptions. The diamagnetic nickel(II) and zinc complexes also showed reduced diatropic character compared to typical nickel(II) and zinc porphyrins.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Indene, ≥99%
Sigma-Aldrich
2-Indanone, 98%
Sigma-Aldrich
Indene, contains 50-100 ppm tert-butylcatechol as stabilizer, technical grade, ≥90%
Sigma-Aldrich
Indene, 98%