Azide-based in situ preparation of fused heterocyclic imines and their multicomponent reactions.

Structurally diverse pyrroles, indoles and imidazoles bearing an N-ω-azidoalkyl moiety and an aldehyde or ketone function were prepared and successfully introduced into in situ imine generation via the intramolecular Staudinger/aza-Wittig tandem reaction. Reduction of the generated imines led to medicinally relevant nitrogen-containing fused heterocycles such as tetrahydropyrrolo[1,2-a]pyrazines and diazepines. Rare 8-membered hexahydropyrrolo[1,2-a][1,4]diazocine and 9-membered dihydro-4,8-(metheno)pyrrolo[1,2-a][1,4]diazacycloundecine were also synthesized. In addition, several one-pot transformations involving cyclic anhydrides or isocyanides (Castagnoli-Cushman, Ugi and azido-Ugi reactions) were added to the Staudinger/aza-Wittig sequence to afford novel fused polyheterocyclic delta-lactams, cyclic bisamides and tetrazoles in a multicomponent fashion. The synthesized compounds were profiled against human Trace Amine-Associated Receptor 1 (hTAAR1), and the best performing compound showed low nanomolar agonistic activity with an EC50 of 0.025 µM.

In situ generation of imines by the Staudinger/aza-Wittig tandem reaction combined with thermally induced Wolff rearrangement for one-pot three-component ß-lactam synthesis.

A new efficient protocol for diastereoselective three-component one-pot lactam synthesis involving the in situ generation of imines via the Staudinger/aza-Wittig tandem reaction combined with the Wolff-rearrangement and ketene-imine cycloaddition was developed to produce a series of 24 novel structurally diverse ß-lactam- or 1,3-oxazine-products. It was shown that this synthesis can be performed both as a two step-procedure and true MCR with simultaneous loading of all reactants. The intramolecular version of the 1st step provided facile access to seven-membered cyclic imines, which allowed further preparation of a series of rare tricyclic ß-lactams. For the intermolecular version of the 1st step (acyclic imine generation), it was shown that the outcome of the synthesis is different from that using pre-synthesized and isolated imines. Additionally, this is the first example of the implementation of the Staudinger/aza-Wittig tandem reaction for the preparation of four-membered heterocycles.

One-Pot Sequence of Staudinger/aza-Wittig/Castagnoli-Cushman Reactions Provides Facile Access to Novel Natural-like Polycyclic Ring Systems.

Realization of the one-pot Staudinger/aza-Wittig/Castagnoli-Cushman reaction sequence for a series of azido aldehydes and homophthalic anhydrides is described. The reaction proceeded at room temperature and delivered novel polyheterocycles related to the natural product realm in high yields and high diastereoselectivity. The methodology has been extended to three other cyclic anhydrides. These further unravel the potential of the Castagnoli-Cushman reaction in generating polyheterocyclic molecular scaffolds.