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

Abstract

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 1H, 13C NMR, IR and MS spectra, while their molecular structures are elucidated by X-ray crystallography of a selected sample.

2-Azaallyl Anions, 2-Azaallyl Cations, 2-Azaallyl Radicals, and Azomethine Ylides

“…As was introduced in section , decarboxylation is a relatively mild and powerful strategy for the generation of semistabilized 2-azaallyl anions. Similarly, the tandem iminium condensation/thermal decarboxylation reaction manifold (via carboxylic acids 278 , Scheme ) is a popular method for in situ preparation of N -alkyl azomethine ylides. − In 1993, Prato and co-workers demonstrated that C 60 could be converted to the corresponding pyrrolidine by 1,3-dipolar cycloaddition with the N -methyl azomethine ylide generated via thermal decarboxylation of the iminium formed by condensation between sarcosine ( N -methlyglycine) and formaldehyde (Scheme ). This so-called “Prato reaction”, and variations thereof, have since been applied toward the functionalization of fullerenes, − graphene and single-walled carbon nanotubes and nanohorns, − …”