Fluorescent Azasteroids through Ultrasound Assisted Cycloaddition Reactions

Abstract

We report here the synthesis and optical spectral properties of several new azasteroid derivatives. The formation of these compounds was explained based on the most probable mechanism. The luminescent heterocycles were synthesized by 1,3-dipolar cycloaddition reactions between benzo[f]quinoline and methylpropiolate or dimethyl acetylenedicarboxylate (DMAD). A selective and efficient way for [3+2]-dipolar cycloaddition of benzo[f]quinolinium ylides under ultrasound (US) irradiation (20 kHz processing frequency) is presented. We report substantially higher yields under US irradiation, whereas the solvent amounts required are at least three-fold less compared to classical heating. The azasteroid derivatives are blue emitters with λmax of fluorescence around 430–450 nm. A certain influence of the azasteroid substituents concerning absorption and fluorescent properties was observed. Compounds anchored with a bulky pivaloyl group or without a C=O carbonyl group have shown increased fluorescence intensity.

Ultrasound-Assisted Synthesis of Fluorescent Azatetracyclic Derivatives: An Energy-Efficient Approach

“…In the present study, we applied this functionalization to the azatetracyclic derivatives that we previously obtained [ 37 ]. Thus, the tetracyclic cycloadduct products 1a – d were subjected to the bromination in heterogeneous catalysis using copper (II) bromide in chloroform/ethyl acetate, as is presented in Scheme 1 .…”

“…The bromo derivatives with increased reactivity are valuable intermediary in synthetic chemistry, because they could be used as alkylating agents for direct chemical labelling of proteins targets cysteine and amine groups. Moreover, these brominated products can be easier converted to the corresponding azides using the procedure described in the literature [ 37 , 38 ]. The resulted azides are also highly valuable intermediary in synthetic chemistry since they can be used in the click chemistry, being extraordinary stabled toward H 2 O, O 2 , and the majority of organic synthesis condition [ 39 ].…”

“…The alteration of the planar structure of the molecule determines a decrease in fluorescence. This fact can be observed when comparing the fluorescence intensity of the bromides 2a – d versus azides 4a – d , and also if we compare the fluorescence intensity of the underivatized cycloadducts 1a – d with the fluorescence intensity of the derivatized azatetracyclic bromides 2a – d or azides 4a – d [ 37 ].…”

“…Our group focused on the dipolar cycloaddition reactions of azinium ylides with various dipolarophiles in order to obtain new compounds with fluorescent properties and biological activities [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. We also added additional contributions in the field of using US irradiation in organic synthesis [ 1 , 2 , 3 , 4 , 5 , 37 ]. Herein, we propose a facile, efficient, and environmentally friendly method using US irradiation for the derivatization of previously obtained blue-emitting derivatives.…”

A Review on the Synthesis of Fluorescent Five- and Six-Membered Ring Azaheterocycles

“…Several compounds with complex azaheterocyclic skeleton were synthesized through the N-ylides. Many of these compounds present practical importance either to their biological activities, having antimicrobial [ 40 , 41 ], anticancer [ 42 , 54 , 55 , 56 , 57 , 58 ], antitubercular [ 58 , 59 , 60 , 61 ] or anti-leishmaniasis [ 62 ] activity, or to their optical properties (some of this compound presenting intense blue fluorescence) [ 63 , 64 , 65 , 66 , 67 , 68 , 69 ]. Here we will present our recent (last 12 years) achievements in the synthesis of fluorescent azaheterocyclic compound.…”