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C-H Activation and Alkyne Annulation via Automatic or Intrinsic Directing Groups: Towards High Step Economy.

Direct transformation of carbon-hydrogen bond (C-H) has emerged to be a trend for construction of molecules from building blocks with no or less prefunctionalization, leading high atom and step economy. Directing group (DG) strategy is widely used to achieve higher reactivity and selectivity, but additional steps are usually needed for installation and/or cleavage of DGs, limiting step economy of the overall transformation. To meet this challenge, we proposed a concept of automatic DG (DGauto ), which is auto-installed and/or auto-cleavable. Multifunctional oxime and hydrazone DGauto were designed for C-H activation and alkyne annulation to furnish diverse nitrogen-containing heterocycles. Imidazole was employed as an intrinsic DG (DGin ) to synthesize ring-fused and π-extended functional molecules. The alkyne group in the substrates can also be served as DGin for ortho-C-H activation to afford carbocycles. In this account, we intend to give a review of our progress in this area and brief introduction of other related advances on C-H functionalization using DGauto or DGin strategies.