BF₃·OEt₂‐Mediated 1,3‐Hydride Shift Followed by 6π Electrocyclization: An Efficient Route for the Synthesis of Pyridopyrimidine, Pyranoquinoline, and Phenanthroline Derivatives

Abstract

The synthesis of pyridopyrimidine, pyranoquinoline, and phenanthroline derivatives can be easily and efficiently accomplished by the direct reaction of a 1‐aminopenta‐1,4‐diene fragment, an aromatic aldehyde, and BF3·OEt2 in the absence of any metal catalyst. The notable features of this procedure are mild reaction conditions, good to high yields, and operational simplicity.

Metal‐Free and Mild Synthesis of 2,4‐Diarylquinolines

“…For example, Yan, [10] Ambarasan, [11] Nan, [12] and Ma [13] groups recorded a series of relevant synthesis routes depending on the transition metals, I 2 or acid catalytic systems (Scheme 1a). Helaja, [14] Baine, [15] Zhao, [16] and Nandi [17] groups used precursors with functional groups of the required position to synthesize quinoline compounds (Scheme 1b). However, existing syntheses are prevalent in requiring high temperatures, long reaction times, catalyst contamination, high costs or potential side reactions.…”

Indium(III) Chloride Catalyzed Convergent, Regioselective Synthesis of Annulated Quinoline and Pyridine Derivatives

“…19 Its potential as a Lewis acid catalyst for fundamental reactions, such as the Diels-Alder, 20 Friedel-Crafts, 21 Mukaiyama aldol, 22 and SakuraiHosomi allylation reactions, 23 has been extensively investigated. 24 Literature search reveals that addition of carbon-carbon double bond to imine bond by indium(III) catalyst 25 is quite rare.We indeed recently demonstrated the synthesis of pyridine derivatives from 1-aminopenta-1,4-diene fragment and aromatic aldehyde by BF 3 ·OEt 2 -mediated reaction, 26 where the yield of product varied with catalyst loading, and better results were achieved only by using as high as 40 mol% BF 3 ·OEt 2. along with pyrrole derivatives as side product (Scheme 1).These results prompted us to search for an improved and efficient protocol to access the potentially bioactive pyridine-annulated scaffolds exclusively. Indium-catalyzed, This document was downloaded for personal use only.…”

“…We indeed recently demonstrated the synthesis of pyridine derivatives from 1-aminopenta-1,4-diene fragment and aromatic aldehyde by BF 3 •OEt 2 -mediated reaction, 26 where the yield of product varied with catalyst loading, and better results were achieved only by using as high as 40 mol% BF 3 •OEt 2. along with pyrrole derivatives as side product (Scheme 1).…”

“…Earlier, pyridopyrrole derivatives were isolated as a side product from the reaction of 4 and 2 when BF 3 •OEt 2 was used in place of InCl 3 . 26 This pyrrole derivative was obtained exclusively when nitro-group-containing aldehydes were used. But in our present work pyridopyrimidine derivatives are obtained exclusively by the indium(III) chloride catalyzed reaction.…”

Phenanthrenequinone-Sensitized Photocatalytic Synthesis of Polysubstituted Quinolines from 2-Vinylarylimines

“… 1 One classic example of such a reaction is electrocyclization, which is applicable for a wide range of starting materials to give access to polysubstituted quinolines ( Scheme 1 a). However, the main drawback of this protocol is the need for harsh reaction conditions, for instance, high temperatures or pressures, 2 strong Lewis acid catalysts, 3 or short wavelength UV lights. 4 Yields typically vary from poor to good with long reaction times up to several days, while dihydroquinolines are often received as side products.…”