Ultrasound-promoted regioselective and stereoselective synthesis of novel spiroindanedionepyrrolizidines by multicomponent 1,3-dipolar cycloaddition of azomethine ylides

A series of novel spiroindanedionepyrrolizidines have been synthesized by multicomponent 1,3-dipolar cycloaddition of a variety of (E)-3-aryl-1-(thiophen-2-yl)prop-2-en-1-ones with unstabilized azomethine ylides generated from ninhydrin and l-proline. The reactions were highly regioselective and stereoselective and were conducted with both conventional heating and ultrasonic irradiation conditions. In general, milder conditions, and moderate improvement in rates, reaction times, and yields were observed when the reactions were performed under ultrasonic conditions. The regioselective and stereoselective nature of the products was established by use of single-crystal X-ray structure and spectroscopic techniques.