Fig. 2. Cu-catalyzed reductive coupling of cyclobutanone oxime ester with terminal alkynes.

[a] 1a (0.2 mmol), 3 (0.4 mmol), CuI (0.1 equiv), tBu₃-TERPY (0.2 equiv), K₂CO₃ (2.0 equiv), CH₃CN (1.0 mL, c 0.2 M), 60 °C, under nitrogen atmosphere. Yields refer to the isolated products. [b] Reaction performed at 2.0 mmol scale.