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Carboxylate Ligand Exchanged Amination/C(sp3)-H Arylation Reaction via Pd/Norbornene Cooperative Catalysis Bo-Sheng Zhang, Yuke Li, Yang An, Zhe Zhang, Ce Liu, Xin-Gang Wang, and Yong-Min Liang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b04163 • Publication Date (Web): 12 Nov 2018 Downloaded from http://pubs.acs.org on November 12, 2018
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ACS Catalysis
Carboxylate Ligand Exchanged Amination/C(sp3)-H Arylation Reaction via Pd/Norbornene Cooperative Catalysis Bo-Sheng Zhang,1‡ Yuke Li,2‡ Yang An,1 Zhe Zhang,1 Ce Liu,1 Xin-Gang Wang,1 Yong-Min Liang*1 1State
Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China of Chemistry and Centre for Scientific Modeling and Computation, Chinese University of Hong Kong, Shatin, Hong Kong, China 2Department
ABSTRACT: This report describes a carboxylate ligand exchange strategy that was used to achieve a Catellani reaction consisting of amination/unactivated aliphatic C-H arylation. Pivalic acid was used as an additive that could promoted effectively C-H activation of unactivated alkanes without affecting the key five-membered aryl-norbornene-palladacycle (ANP) intermediate. Importantly, the reaction demonstrates high regioselectivity for the primary carbon. Following ortho-amination, the carboxylic acid was found to coordinate palladium in a bidentate fashion, and the pathway and driving force of carboxylic acid exchange was explored using density functional theory (DFT) calculations. Keywords: Norbornene; Arylation; Ligand Exchange; Amination; CMD; C-H activation; Palladium.
Palladium catalyzed C-H bond activation is considered an important area of research in organic chemistry. 1 Various directing groups DG, ligands, and additives have been shown to participate in the palladium-catalyzed concerted metalation deprotonation (CMD) process and were discovered through the joint efforts of several C-H activation scholars and researchers. To expand the scope of C-H activation reaction, many studies have focused on improving the DG, for example, by making the DG easier to access, remove or modify.2 In particular, some reports have used a unique DG to achieve selective remote C-H activation.3 Other studies focused on the effects of additives 4 and ligands5 such as carboxylic acids4a, 4b, chiral phosphoric acids4c, norbornenes6 and pyridine derivatives6 on the reaction mechanism, regioselectivity and stereoselectivity.7 It is noteworthy that the functionalization of unactivated aliphatic C-H reaction often requires specific ligands, additives and even mixed solvents that are typically not compatible with other types of reactions. Therefore, multistep tandem reactions that functionalize unactivated aliphatic C-H bonds remain a synthetic challenge that is difficult to realize. Catellani discovered Pd/NBE chemistry in 1997.8a Lautens firstly used phosphine ligands to solve the compatibility problem of Pd/NBE chemistry in 2000 and established Pd/NBE/ligands Catellani-Lautens reaction system.8b A variety of ortho-position functionalizations, such as ortho alkylation, arylation, carbonylation and amination, were fulfilled by Catellani9, Lautens10, Dong11, Bach12, Zhou13, Gu14 and others15. Among them, Dong group achieved ortho-amination for the first time in 2013, and its leaving group (carboxylic acids) attracted our attention when we wanted to solve Catellani reaction compatibility problem of the sp3-C-H activation. 11g Indeed, the new nu-
cleophilic reagents (Nu) that terminate the reaction cascade including carbenes16, tandem cyclizations17, dearoma-
Scheme 1. Carboxylate Ligand Exchanged Amination/C(sp3)-H Arylation Reaction via Pd/Norbornene Catalysis.
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Table 1. Carboxylic Acid and Carboxylate Ligand Exchanged Effect for Amination/C(sp3)-H Arylation Reaction.a
GC yield of 6, 7, 5, 4, 3a
entry
catalyst
amination reagent
carboxylic acidb
6
7
5
4
3a
yieldc (3a)
1 2
Pd(OAc)2/PPh3 Pd(OAc)2/PPh3
2a 2aa
-
7 7
0 0
13 2
47 51
16 29
13 26
3 4
Pd(OAc)2/PPh3 Pd(OAc)2/PPh3
2ab 2ac
-
18 8
0 0
39 4
36 52
4 21
