Remote C-H insertion of vinyl cations leading to cyclopentenones

We report a Lewis acid catalyzed reaction sequence involving a 1,2-shift and subsequent C-H insertion that gives monocyclic and fused bicyclic cyclopentenone products. This reaction sequence, which is initiated by treating β-hydroxy-α-diazo ketones with a Lewis acid, proceeds through vinyl cation intermediates that insert at non-activated gamma C-H bonds. This reaction represents an alternative strategy to exploit the diazo functional group in an intramolecular C-H insertion, and can provide products not accessible by transition metal catalyzed C-H insertions. This remote C-H activation process provides good yields of bicyclic cyclopentenone products that contain 7- and 8-membered rings, and monocyclic prostaglandin analogs.