Carbamates widely exist in natural products, drugs and pesticides, and have also been utilized as directing groups in the C-H bond activation. Generally, in the presence of transition metals, the carbamate group can selectively direct the ortho C-H bond activation of substrates to realize the coupling approaches with various coupling reagents through metal-bearing six-membered ring intermediates. The application of carbamates in the C-H bond activation reactions has been systematically summarized, including:(1) sp² C-H bond activation and functionalization of N-aryl carbamates, and aryl carbamates under the catalysis of Pd, Rh, Ru, or Ir to afford the corresponding halogenation, arylation, cyclization, and alkenylation products;(2) sp² C-H bond activation and functionalization of alkenyl carbamates in the presence of Rh to afford the corresponding alkenylation and allylation products;(3) sp³ C-H bond activation and functionalization of N-dialkyl carbamates in the presence of Pd, Cu, Fe or even the transition-metal-free conditions to afford the acetoxylation, alkylation or arylation products. During the aromatic sp² C-H bond activation approaches, both electronic and steric effects control the reaction yields and regioselectivities. In most cases, substrates bearing electron donating and less steric hindrance groups show better reactivity. Moreover, owing to the high activity of vicinal position of amines, the C-H functionalization of benzylamine, tetrahydroisoquinolines or 1,2-dihydroquinoline, bearing N-alkoxycarbonyl, can be carried out under the catalysis of copper, iron, or even the transition-metal-free conditions, some of which can also show high enantioselectivity through the asymmetric induction. The review can provide some guidance to promote the further development and application of carbamates in C-H bond activation reactions.
Contents
1 Introduction
2 Ortho-directed sp² C-H bond activation reactions of N-aryl carbamates
2.1 Pd-catalyzed reactions
2.2 Rh-catalyzed reactions
2.3 Ru-catalyzed reactions
2.4 Ir-catalyzed reactions
3 Ortho-directed sp² C-H bond activation reactions of aryl carbamates
3.1 Pd-catalyzed reactions
3.2 Rh-catalyzed reactions
3.3 Ru-catalyzed reactions
3.4 Ir-catalyzed reactions
4 Ortho-directed sp² C-H bond activation reactions of N-alkenyl carbamates and alkenyl carbamates
5 Directing sp³ C-H bond activation reactions of N-dialkyl carbamates
6 Non-directing sp³ C-H bond activation reactions of N-dialkyl carbamates
7 Conclusion