A trans-AB-bacteriochlorin building block.
Synthetic bacteriochlorins are of interest for fundamental studies in photochemistry because of their strong absorption in the near-infrared spectral region and close similarity with natural bacteriochlorophylls. A de novo route to 5-methoxybacteriochlorins entails self-condensation of a dihydrodipyrrin-acetal, which in turn is prepared from a 2-(2-nitroethyl)pyrrole species and an α,β-unsaturated ketone-acetal (e.g., 1,1-dimethoxy-4-methylpent-3-en-2-one). Here, four new results are reported concerning the synthesis of substituted bacteriochlorins. First, a new, scalable route to 1,1-dimethoxy-4-methylpent-3-en-2-one removes a significant previous impediment to the overall route. Second, the new route was employed to gain access to new α,β-unsaturated ketones and corresponding dihydrodipyrrins bearing alternative substituents in place of the dimethoxy unit. Third, a dihydrodipyrrin bearing a 1,3-dioxolan-2-yl moiety afforded the bacteriochlorin (30% yield) containing a 2-hydroxyethoxy substituent at the 5-position. Fourth, subsequent bromination proceeded regioselectively at the 15-position to give a trans-(5,15)-AB-bacteriochlorin building block. The linear 5,15-substitution pattern is attractive for a number of molecular designs. The results taken together afford deeper understanding of the scope and limitations of the de novo route and also advance the capabilities for tailoring synthetic bacteriochlorins.
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
Olga
O
Mass
Jonathan S
JS
Lindsey
D000080:Acetals / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D054879:Halogenation; D015394:Molecular Structure; D010777:Photochemistry; D011166:Porphyrins / Q000138:chemical synthesis* / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry*
C570129:2-(2-nitroethyl)pyrrole; D000080:Acetals; D011166:Porphyrins; D011758:Pyrroles; C452433:bacteriochlorin