Abstract
We report here the synthesis and optical spectral properties of several new pyrrolodiazine derivatives. The luminescent heterocycles were synthesized by 1,3-dipolar cycloaddition reactions between N-alkylated pyridazine and methylpropiolate or dimethyl acetylenedicarboxylate (DMAD). The pyrrolopyridazine derivatives are blue emitters with moderate quantum yields (around 25%) in the case of pyrrolopyridazines and negligible yet measurable emission for pyrrolophthalazines. In a subsequent step towards including the pyrrolodiazine moiety, given its spectral properties in various macromolecular frameworks such as biological molecules, a subset of the synthetized compounds has been subjected to α-bromination. A selective and efficient way for α-bromination in heterogeneous catalysis of pyrrolodiazine derivatives under microwave (MW) irradiation is presented. We report substantially higher yields under MW irradiation, whereas the solvent amounts required are at least five-fold less compared to classical heating.
Highlights
Pyrrolodiazines are an important class of N-bridgehead heterocycles which have received increasing interest during the last few years driven by a wide range of potential applications, from electroluminescent materials [1] to interesting biological uses [2]
The general approach adopted for the synthesis of fluorescent pyrrolodiazine derivatives is depicted in Scheme 1
The preparation of all pyrrolodiazine derivatives, 7–11, involves two steps: initially N-alkylation of the diazine with bromoacetone 3 followed by a 3 + 2 dipolar cycloaddition of diazinium ylides 6 from the corresponding salts to the corresponding dipolarophiles
Summary
Pyrrolodiazines are an important class of N-bridgehead heterocycles which have received increasing interest during the last few years driven by a wide range of potential applications, from electroluminescent materials [1] to interesting biological uses [2]. The interest in the field of pyrrolodiazine derivatives arises from their highly efficient blue fluorescence emission [9,10,11] The latter property makes pyrrolodiazine derivatives very attractive materials in optoelectronics for blue organic light-emitting diodes [9,10,11], whereas a combined use of the two distinct properties has suggested interesting applications as fluorescent biomarkers [12,13,14]. Azaindolizines derivatives represent such a class (with 10 π-electron N-fused heterocycles, containing a bridgehead nitrogen atom shared by an electron-excessive pyrrole and a diazine electron deficient six-membered ring) being a ‘pure’
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