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N-Arylation of Carbamates through Photosensitized Nickel Catalysis. Leleti Rajender Reddy, Sharadsrikar Kotturi, Yogesh Waman, Vudem Ravinder Reddy, Chirag Patel, Ajinath Kobarne, and Sasikumar Kuttappan J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 09 Oct 2018 Downloaded from http://pubs.acs.org on October 9, 2018
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The Journal of Organic Chemistry
N-Arylation of Carbamates through Photosensitized Nickel Catalysis. Leleti Rajender Reddy,* Sharadsrikar Kotturi, Yogesh Waman, Vudem Ravinder Reddy, Chirag Patel, Ajinath Kobarne and Sasikumar Kuttappan. Piramal Discovery Solutions, Pharmaceutical Special Economic Zone, Sarkhej Bavla Highway, Ahmedabad, Gujarat 382213, India.
[email protected] Cbz-NH2 or Boc-NH2
Br +
NHCbz or
Ir, Ni
NHBoc
Blue LED room temperature broad FG tolerance user friendly and scalable inexpensive and ready available Cbz-amine or Boc-amine easily removable protecting groups
Abstract A highly efficient method of visible light mediated Ni (II) catalyzed photoredox N-arylation of Cbz-amines / Boc-amines with aryl electrophiles at room temperature is reported.
The
methodology provides a common access to a wide variety of N-aromatic and N-heteroaromatic carbamate products that find use in the synthesis of several biologically active molecules and provides a distinct advantage over traditional palladium catalysed Buchwald reaction. Introduction Visible light mediated photoredox catalysis has recently emerged as a powerful activation strategy for the discovery and invention of new organic transformations affording valuable molecules in a safe, inexpensive, non-polluting, and thus potentially sustainable manner.1 Professor Deronzier,2 reported the first synthetic application of ruthenium photocatalysted Pschorr-type transformation
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via single electron transfer (SET) process. In recently, several groups started reporting the direct photoexcitation of transition-metal catalyzed synthetic transformation to demonstrate this paradigm.3 In particularly, Professor MacMillan’s sophisticated report on C-N bond formation of aryl bromide with amines using Ni(II) salts and photoredox catalysis is the best alternative for Buchwald–Hartwig reaction.4 Later, Professor MacMillan also published the N-arylation of sulfonamides with aryl electrophiles via photosensitized Ni (II) catalysis.5 Inspired by the work of Professor MacMillan, we reasoned that N-arylation / heteroarylation of carbamates through photosensitized nickel catalysis could be a viable alternative for Buchwald-Hartwig N-arylation of carbamates cross-coupling reaction (Scheme 1).6
Herein, we disclose the N-arylation /
heteroarylation of carbamates under Ni (II) catalyzed photoredox conditions. Scheme 1. Nickel-catalyzed of N-arylation of carbamates. a) MacMillan's work for Photocatalysed Approach to Amination of Aryl Halides H Br R1 N Ir, Ni 1 H 2N R + Blue LED b) MacMillan's work for Photocatalysed Approach to Sulfonamidation of Aryl Halides H Br O O R1 N Ir, Ni S S 1 + H 2N R O O Blue LED c) This work for Photocatalysed Approach to Carboamidation of Aryl / Hetereoaryl Halides Cbz-NH2 or
Br +
Blue LED
Boc-NH2 1
NHBoc
NHCbz or
Ir, Ni
2
3 room temperature broad FG tolerance user friendly and scalable
4
inexpensive and ready available Cbz-amine or Boc-amine easily removable protecting groups
Results and discussion At the outset of our investigation, we chose the 3-bromobenzonitrile (2a) and Cbz-amine (1a) as
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The Journal of Organic Chemistry
our model substrates. We began studying the proposed C-N bond formation reaction of 3bromobenzonitrile (2a) with Cbz-amine (1a) with emphasis on the development of a user-friendly and scalable method. Fortunately, we found that the commercial bench-stable precatalyst systems Ir(ppy)2(bpy)PF6 and NiCl2·glyme with 4,4’-di-t-butyl-2,2’-bipyridine ligand (dtbbpy) combined with two equivalents of base (tetramethylguanidine, TMG) in CH3CN under irradiation with blue LED (34 W) enabled the aryl amine (3a) in 93% yield (Table 1, entry 1). Based on the control experiments, it has been found that both nickel and blue light presence were vital for the product formation (Table 1). It has been also noticed that in the absence of photocatalyst, trace quantity (
