Ultrasound-promoted synthesis of novel dispirocyclic frameworks from aza-Claisen rearrangements of Baylis-Hillman amines

A novel tetracyclic frameworks of dispiropyrrolizidines can be obtained in moderate to good yields via the 1,3-dipolar cycloaddition of azomethine ylides with dipolarophiles derived from aza-Claisen rearrangement of Baylis-Hillman amines. The transformations are highly regioselective and stereoselective, affording the desired compounds in reduced time and increased yields under ultrasound irradiation at room temperature. All the products are confirmed by H-1, C-13 NMR, IR and MS spectra, while their molecular structures are elucidated by X-ray crystallography of a selected sample. (C) 2008 Elsevier B.V. All rights reserved.