O-Acyl oximes: versatile building blocks for N-heterocycle formation in recent transition metal catalysis

O-Acyl oximes are versatile building blocks being widely applied in organic synthesis, especially for N-heterocycle construction under transition metal catalysis. In the last decade, aza-Heck cyclization using oximes has been progressing in the preparation of functionalized pyrrolines, and instead of Pd catalysis, copper-based catalytic systems were found to work well in some cases. O-Acyl oximes as oxidizing directing groups have attracted intensive attention in transition metal-mediated C-H activation reactions, which avoid the use of external oxidants to feature advantages including mild reaction conditions, higher levels of reactivities, chemo-selectivities, etc. Moreover, catalytic α C(sp(3))-H functionalization of O-acyl oximes and subsequent annulations provide a lot of opportunities for novel N-heterocycle synthesis. These transformations feature certain advantages: diversified and poly-functionalized products, mild and easy handling conditions, oximes serving as an internal oxidant to avoid the use of external oxidants, and so forth.