Journal
JOURNAL OF PORPHYRINS AND PHTHALOCYANINES
Volume 13, Issue 10, Pages 1098-1110Publisher
WORLD SCI PUBL CO INC
DOI: 10.1142/S1088424609001406
Keywords
chlorin; bacteriochlorin; bromination; dihydrodipyrrin; tetrahydrodipyrrin; McMurry cyclization; Michael addition
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Funding
- Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Science, Office of Science, U.S. Department of Energy [DE-FG02-96ER14632]
- National Institute of Allergy and Infectious Diseases [R41AI072854]
- NIAID
- NIH
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Bromo-substituted hydrodipyrrins are valuable precursors to synthetic bromo-chlorins and bromo-bacteriochlorins, which in turn are versatile substrates for derivatization in pursuit of diverse molecular designs. 8-bromo-2,3-dihydro-1-(1,1-dimethoxymethyl)-3,3-dimethyldipyrrin (1) is a crucial precursor in the rational synthesis of the bacteriochlorin building block 3,13-dibromo-8,8,18,18-tetramethylbacteriochlorin (H2BC-(BrBr13)-Br-3). 8-bromo-2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin (2) is a crucial precursor in the rational synthesis of the analogous 3,13-disubstituted chlorin building block (e.g. H2C-(BrMBr13)-M-3-Br-10). The routes to 1 and 2 share a common precursor, namely 4-bromo-2-(2-nitroethyl)-1-N-tosylpyrrole (6-Ts), which is derived from pyrrole-2-carboxaldehyde. The prior seven-step synthesis of 1 from pyrrole-2-carboxaldehyde has limited access to H2BC-(BrBr13)-Br-3 given the large excesses of materials, extensive reliance on column chromatography, and low overall yield (1.4%). Refined procedures for synthesis of the common precursor 6-Ts as well as 1 and 2 afford the advantages of (1) diminished consumption of solvents and reagents, (2) limited or no use of chlorinated solvents, (3) limited or no chromatography, and (4) improved yields of most steps. Streamlined procedures enable the final two or three transformations to be performed without purification of intermediates. The new procedures facilitate the expedient preparation of 1 and 2 at the multigram scale.
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