Intramolecualr cyclization of a dipyrromethane by an electrophilic aromatic substitution reaction producing a new chiral compound

Abstract

Dipyrromethane 2 functionalized with 3-chloropropyl group on the meso carbon undergoes an unusual intramolecular electrophilic aromatic substitution reaction in the presence of $NaN_3$ instead of a simple nucleophilic substitution reaction. As a result, a new chiral dipyrromethane 1 was synthesized. In this reaction, the ${\beta}$-carbon of the pyrrole ring functions as a nucleophile while the carbon next to the chlorine atom acts as an electrophile. Interestingly, this reaction progresses even in the absence of an acid catalyst. Compound 1 was fully characterized by $^1H-^1H$ and $^1H-^{13}C$ COSY NMR spectroscopic analyses and the high resolution EI mass spectrometry.

Figure 1. Partial ¹H-¹H homonuclear COSY NMR spectrum of compound 1 recorded in CDCl₃.

Figure 2. Partial ¹H-¹³C heteronuclear COSY NMR spectrum of compound 1 recorded in CDCl₃.

Figure 3. Partial ¹H-¹H COSY NMR spectrum of compound 1 recorded in CDCl₃.

Figure 4. Partial ¹H-¹³C COSY NMR spectrum of compound 1 recorded in CDCl₃.

Scheme 1. Synthesis of compound 1