59th Annual Report on Research 2014

Bismuth compounds in organic synthesis. Bismuth bromide catalyzed one-pot synthesis of polyhydroquinoline derivatives.

We first investigated the iron(III) tosylate catalyzed one-pot synthesis of polyhydroquinolines via a multicomponent synthesis (The Hantzsch reaction). However, initial results were not as promising as they were for some other reactions carried out in the group using iron(III) tosylate. Due to our interest in polyhydroquinoline, we continued screening other catalysts and found that the best results were obtained with bismuth(III) bromide. All reactions were carried out at room temperature or 50° C when slow at room temperature. Product was obtained in good to excellent yields after recrystallization or simply washing with ethanol/water (1:1). The use of a non toxic bismuth salt, and a relatively green solvent, ethanol make this method particularly attractive from a green chemistry perspective. These results are quite promising and we expect to publish a manuscript based on this work in the near future.

Table 1. Synthesis of polyhydroquinoline derivatives catalyzed by BiBr₃

Entry		R1		R2		R3		Time and T (°C)		Yield (%)
1		p-CH3		CH3		CH3CH2		3.5 h, rt		87
2		p-OCH3		CH3		CH3CH2		23 h, rt		87
3		p-N(CH3)2		CH3		CH3CH2		4 h, 50° C		86
4		p-Cl		CH3		CH3CH2		2.5, rt		93
5		p-NO2		CH3		CH3CH2		17 h, rt		87
6		m-OCH3		CH3		CH3CH2		2 h, 50° C		90
7		m-CH3		CH3		CH3CH2		5.5, rt		86
8		p-NO2		CH3		CH3CH2		17 h, rt		78
9		2-Furyl		CH3		CH3CH2		4 h. rt		87
10		p-C6H4		CH3		CH3CH2		3.5, 50° C		91