Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles.

Ramazan Koçak,Arif Daştan

doi:10.3762/bjoc.17.61

Abstract

The synthesis of novel polycyclic π-conjugated dihydropyridazines, pyridazines, and pyrroles was studied. Dihydropyridazine dyes were synthesized by inverse electron-demand Diels–Alder cycloaddition reactions between a dibenzosuberenone and tetrazines that bear various substituents. The pyridazines were synthesized in high yields by oxidation of dihydropyridazine-appended dibenzosuberenones with PIFA or NO. p-Quinone derivatives of pyridazines were also obtained by H-shift isomerization following the inverse electron-demand Diels–Alder reaction of tetrazines with p-quinone dibenzosuberenone. Then these pyridazines were converted to the corresponding pyrroles by reductive treatment with zinc. It was observed that all the dihydropyridazines obtained gave absorbance and emission at long wavelengths.

Highlights

Π-Conjugated polycyclic hydrocarbons (CPHs) containing polycyclic heteroaromatic molecules (PHAs) and aza-polycyclic aromatic hydrocarbons have been attracting considerable attention as they are widespread in natural products, as well as in pharmaceuticals, agrochemicals, and organic materials
Due to these unique features, the synthesis of new dihydropyridazines, pyridazines, and pyrroles, which have the potential to be used in many applications, is very important. inverse electron-demand Diels–Alder cycloaddition reactions of alkenes with tetrazines are commonly used for the synthesis of dihydropyridazines and pyridazines [50,51,52,53,54]
In the first part of the study, we focused on the inverse electrondemand Diels–Alder cycloaddition reactions of dibenzosuberenone (1) with s-tetrazines 2a–l (Figure 2), which were synthesized according to the literature procedures (2j was synthesized by acetylation of 2i, while 2b and 2g were purchased) [57,58,59,60,61,62,63]

Summary

Introduction

Π-Conjugated polycyclic hydrocarbons (CPHs) containing polycyclic heteroaromatic molecules (PHAs) and aza-polycyclic aromatic hydrocarbons (aza-PAHs) have been attracting considerable attention as they are widespread in natural products, as well as in pharmaceuticals, agrochemicals, and organic materials. We report the examined impact of various electronwithdrawing and electron-donating functional groups at the 3and 6-positions of s-tetrazine on inverse electron-demand Diels–Alder cycloaddition reactions with a dibenzosuberenone (1) and the photophysical properties of dihydropyridazines. Inverse electron-demand Diels–Alder cycloaddition reactions of alkenes with tetrazines are commonly used for the synthesis of dihydropyridazines and pyridazines [50,51,52,53,54]. Scheme 1: Inverse electron-demand Diels–Alder reactions of dibenzosuberenone (1) with tetrazines 2a–l.

Results

Conclusion