A one-pot multi component reaction of selenoureas, which are in situ generated from L-amino esters and isoselenocyanates, with α-bromoketone under ultrasonication. Selenourea and α-bromoketones formed 2-iminoselenazoles through a Hantzsch selenazole-type reaction. The steric effect of the α-substituted bromoketones on the rate of the tandem reaction was studied to understand the reaction mechanism by isolating the key reaction intermediate, 2-iminoselenol.