Palladium-catalyzed ortho-olefination of 2-arylpyrrolidines: A tool for increasing structural complexity in nitrogen heterocycles

The dual role of the (2-pyridyl)sulfonyl unit as directing functionality and readily removable N-protecting group has enabled an efficient and practical transformation of 2-arylpyrrolidine derivatives into more complex tricyclic frameworks via palladium-catalyzed ortho-olefination with electron deficient alkenes and subsequent cyclization upon N-deprotection under mild conditions. The key cross coupling step in the presence of N-fluoro-2,4,6-trimethylpyridinium triflate ([F+]) as the terminal oxidant is both highly efficient and tolerant to a variety of steric and electronic changes at both coupling partners. By adequate choice of reductive conditions, the N-sulfonyl deprotection can be directed to the selective formation of benzo-fused pyrrolizidine or fused pyrrolidino-benzazapine frameworks.