Lewis Acid-Catalyzed Formal (4+2)-Cycloaddition between Cross-Conjugated Azatrienes and Styrylmalonates: The Way to Functionalized Quinolizidine Precursors.

Quinolizidine and azaphenalene alkaloids are common in nature and exhibit a pharmaceutical activity, which stirs up increased interest in expanding the range of methods for the synthesis of the corresponding derivatives. In this work, we attempted to adapt our previously presented method for the synthesis of tetrahydropyridines to the preparation of potential precursors for these heterocycles as a separate development of a necessary intermediate stage. To this end, we studied the reactions of ß-styrylmalonates with N-protected cross-conjugated azatrienes in the presence of Sn(OTf)2. Moreover, the regioselectivity of the process involving unsymmetrically substituted azatrienes was estimated. The diene character of vinyltetrahydropyridines was studied in detail with the participation of PTAD. Finally, for the Ts-protected highly functionalized vinyltetrahydropyridines synthesized, a detosylation method to give new desired azadiene structures as precursors of the quinolizidine core was suggested.

Synthesis of a New Family of 1,1-Diazidoethenes: One-Pot Construction of 4-Azido-1,2,3-triazoles via Nitrene Cyclization.

The reaction of 4,4-dichloro-1,2-diazabuta-1,3-dienes with sodium azide has been studied and found to provide straightforward access to extremely rare 1,1-bisazides. It was demonstrated that these highly unstable compounds are prone to eliminate the N2 molecule to cyclize into 4-azido-1,2,3-triazoles bearing two aryl (heteroaryl) groups at positions 2 and 5. The formation of bisazides was confirmed by their trapping with cyclooctyne and B3LYP calculations. Most likely, the elimination of nitrogen to form an intermediate nitrene is facilitated by the aza group via anchimeric-like participation. The reaction was found to be very general for the highly efficient synthesis of various 4-azidotriazoles. It was demonstrated that these heterocycles are highly attractive building blocks for subsequent preparation of 1,2,3-triazole-derived compounds.