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Modular, automated flow synthesis of spirocyclic THNs

Asynt reports that the Cresswell Group, led by Dr Alexander J. Cresswell at the University of Bath, UK, has demonstrated the synthesis of novel spirocyclic tetrahydonaphthyridines (THNs) expanding the chemical space of these important scaffolds for drug discovery. The group is using a combination of photochemistry with flow chemistry to achieve significant results.  

This work shows a novel photoredox-catalysed hydroaminoalkylation (HAA) of halogenated vinyl pyridines, followed by either an intramolecular N-arylation via SNAr, or by a palladium-catalysed C-N bond formation in continuous flow to enable an automated synthesis of α-alkylated and spirocyclic 1,2,3,4-tetrahydro-1,8-naphthyridines (“1,8-THNs”). The key step, the photocatalysed reaction (HAA), was performed using the Uniqsis PhotoSyn. This high-power LED photoreactor lamp module is equipped with a high performance 420nm LED array, which was mounted on a Cold Coil with a 5 mL PFA Coil and cooled to -0.5°C using a Huber CC-805 chiller. The ability to maintain a low temperature with a light intensity of 350 W at 420 nm was a key factor.