CuI-catalyzed sequential diamination and dehydrogenation of terminal olefins: A facile approach to imidazolinones

Article abstract of DOI:10.1002/chem.201404381

Diamination of olefins presents a powerful strategy to access vicinal diamines. During the last decade, metal-catalyzed diamination of olefins has received considerable attention. This study describes an efficient sequential diamination and dehydrogenatio

Full text of DOI:10.1002/chem.201404381

DOI: 10.1002/chem.201404381
Communication
&
Copper Catalysis
CuI-Catalyzed Sequential Diamination and Dehydrogenation of
Terminal Olefins: A Facile Approach to Imidazolinones
Yingguang Zhu and Yian Shi*[a]
Abstract: Diamination of olefins presents a powerful strat-
egy to access vicinal diamines. During the last decade,
metal-catalyzed diamination of olefins has received con-
siderable attention. This study describes an efficient se-
quential diamination and dehydrogenation process of ter-
minal olefins with CuBr as catalyst and di-tert-butyldiaziri-
dinone as nitrogen source, providing a facile and viable
approach to a variety of imidazolin-2-ones, which are im-
portant structural motifs present in various biologically
active molecules.
Diamination of olefins provides a straightforward approach to
Scheme 1. Diamination of terminal olefins.
vicinal diamines, which are contained in a variety of biological-
ly and chemically significant molecules.[1] A number of effective
metal-mediated[2,3] and metal-catalyzed[3c,4–10] diamination pro-
cesses have been reported. In our own studies, we have devel-
oped Pd0[11,12] and CuI-catalyzed[13] diaminations of olefins
using di-tert-butyldiaziridinone (1)[14] as nitrogen source. When
terminal olefin 2 was used as substrate, the diamination with
Pd0 and diaziridinone 1 occurred at allylic and homoallylic car-
bons (Scheme 1).[12] This process likely proceeded via dehydro-
genation of the terminal olefin to form diene intermediate 3,
which was subsequently diaminated in situ to give product
4.[12] In our continuing efforts to explore the reactivity of diazir-
idinone and expand its synthetic utility, we have found that
imidazolin-2-one 7 can be obtained when terminal olefin 5
was treated with 1 and CuBr, likely via a sequential diamination
and dehydrogenation process (Scheme 1). Imidazolin-2-ones
Figure 1. Imidazolinone-containing biologically active compounds.
are important functional moieties present in various biological-
ly active compounds,[15] such as dopamine D4 receptor antago-
nist,[15a] antibacterial MurB inhibitors,[15b] CGRP receptor antago-
nist,[15d] and antitumor agents[15g] (Figure 1). Imidazolin-2-ones
Our initial diamination studies were carried out with styrene
can generally be synthesized by the cyclization of a-amino car-
bonyl compounds, propargylic ureas, and related com-
pounds,[15,16] or by further derivatization of imidazolin-2-
ones.[17] Herein we report our preliminary studies on the CuI-
catalyzed sequential diamination and dehydrogenation process
of terminal olefins.
(5a) as test substrate and di-tert-butyldiaziridinone (1) as nitro-
gen source under various conditions. As shown in Table 1, no
reaction was observed in many cases (Table 1, entries 1–7).
However, when styrene was treated with 10 mol% CuCl and
3.5 equiv of 1 in CH3CN at RT for 9 h, imidazolin-2-one 7a, in-
stead of diamination product 6a, was formed as major product
and isolated in 59% yield (Table 1, entry 8; the X-ray structure
of 7a is shown in Figure 2). The formation of 7a was some-
what unexpected. A slightly higher yield (63%) was obtained
for 7a with CuBr (Table 1, entry 11), and the yield was in-
creased to 85% by slow addition of 1 (Table 1, entry 12).
[a] Dr. Y. Zhu, Prof. Dr. Y. Shi
Department of Chemistry, Colorado State University
Fort Collins, CO 80523 (USA)
E-mail: yian@lamar.colostate.edu
The diamination–dehydrogenation process can be extended
to various para-, meta-, ortho-, and disubstituted styrenes, pro-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201404381.
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Table 1. Studies on reaction conditions.[a]
Table 2. CuBr-catalyzed sequential diamination and dehydrogenation of
terminal olefins.[a]
Yield [%][b]
Entry
Catalyst
Solvent
Yield [%][b]
Entry
Substrate 5
Product 7
1
2
CuCl/P(nBu)3 (1:1)
CuCl
CHCl3
CHCl3
0
0
3
4
5
CuCl
CuCl
CuCl
CH2Cl2
ClCH2CH2Cl
PhH
0
0
0
1[c]
2
3
4
5
6
7
8
5a, X=H
7a
7b
7c
7d
7e
7 f
84
78
87
85
71
80
86
84
6
7
8
9
10
11
12[c]
CuCl
CuCl
CuCl
CuI
CuCN
CuBr
CuBr
PhCH3
THF
0
0
5b, X=p-F
5c, X=p-Cl
5d, X=p-Br
5e, X=p-Me
5 f, X=p-tBu
5g, X=m-Cl
5h, X=o-F
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
59
2
12
63
85
7g
7h
[a] All reactions were carried out with styrene (5a; 0.40 mmol),
1 (1.40 mmol, added in one portion), and CuI catalyst (0.040 mmol) in sol-
vent (0.80 mL) at RT under argon for 9 h, unless otherwise stated. [b] Iso-
lated yield based on styrene. [c] Di-tert-butyldiaziridinone (1) was slowly
added via syringe pump over 7 h, and the reaction mixture was then
stirred for an additional 2 h.
9
88
91
10
11
12
70
88
13
67
14[d]
51
75
Figure 2. X-ray structure of imidazolin-2-one 7a.
viding the corresponding imidazolin-2-ones in 70–91% yield
(Table 2, entries 2–11). Heteroarylethenes, enone, and enyne
were also effective substrates, giving imidazolin-2-ones in 51–
88% yield (Table 2, entries 12–15). The method is amenable to
gram scale as illustrated in the case of imidazolin-2-one 7a
(Table 2, entry 1). As demonstrated in Scheme 2, removal of
tert-butyl group can be achieved with CF3CO2H and concen-
trated HCl. Treating 7a with CF3CO2H at 658C for 5 h resulted
in selective monodeprotection to afford compound 8a in 98%
yield. Both tert-butyl groups were removed in concentrated
HCl at 1008C, giving compound 9a in 87% yield.
15[d]
[a] All reactions were carried out with olefin 5 (0.40 mmol), 1 (1.40 mmol,
added slowly via syringe pump over 7 h), and CuBr (0.040 mmol) in
CH3CN (0.80 mL) at RT under argon for 9 h unless otherwise stated.
[b] Isolated yield. [c] The reaction was carried out on 8.0 mmol scale of
5a. [d] Reaction time, 48 h.
2-one 7a were obtained from styrene (5a) in 23 and 26%
yields, respectively [Scheme 3, Eq. (1)]. The structure of 6a was
confirmed by the X-ray analysis (see the Supporting Informa-
When the reaction was carried out with 1.0 equiv of di-tert-
butyldiaziridinone (1), diamination product 6a and imidazolin-
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monodeprotected as well as completely deprotected. The pres-
ent method provides ready access to imidazolin-2-ones, which
are important functional motifs contained in biologically signif-
icant molecules. Further development of other reaction pro-
cesses with diaziridinone and related compounds is currently
underway.
Experimental Section
Scheme 2. Deprotection of imidazolin-2-one 7a.
Representative procedure for the sequential diamination
and dehydrogenation of olefins (Table 2, entry 1)
A
50 mL single-necked flask charged with CuBr (0.1148 g,
0.80 mmol) was evacuated and filled with argon three times. After
the addition of CH3CN (16 mL) and styrene (5a) (0.8332 g,
8.0 mmol), di-tert-butyldiaziridinone (1; 4.767 g, 28.0 mmol) was
slowly added via syringe pump at RT over 7 h. Upon being vigo-
rously stirred at RT for an additional 2 h, the reaction mixture was
concentrated and purified by flash chromatography (silica gel, pe-
troleum ether/ethyl acetate=20:1 to 15:1 to 10:1) to give imidazo-
linone 7a as a white solid (1.833 g, 84%).
Scheme 3. Mechanistic studies.
Acknowledgements
tion). Treatment of 6a with 1.0 equiv of diaziridinone 1 and
10 mol% CuBr in CH3CN at RT led to imidazolin-2-one 7a in
72% yield [Scheme 3, Eq. (2)]. These results suggest that com-
pound 6a is a possible reaction intermediate for 7a.
We are grateful for the generous financial support from the
General Medical Sciences of the National Institutes of Health
(GM083944-07).
While a precise understanding of the reaction mechanism
awaits further study, a plausible catalytic cycle is proposed in
Scheme 4. The CuBr first reductively cleaves the NÀN bond of
di-tert-butyldiaziridinone (1) to form CuII nitrogen radical
A,[13a,f,18] which adds to terminal olefin 5 to give radical inter-
mediate B. The ring closure of B results in compound 6 and re-
generates CuBr catalyst. Compound 6 is subsequently convert-
ed into imidazolin-2-one 7 by hydrogen abstraction by radical
species A with formation of urea and regeneration of CuBr cat-
alyst.[19]
Keywords: copper
diaziridinone · imidazolinones
·
dehydrogenation
·
diamination
·
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Received: July 13, 2014
Published online on && &&, 0000
&
&
Chem. Eur. J. 2014, 20, 1 – 5
www.chemeurj.org
4
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
COMMUNICATION
The copper age: A sequential diamina-
tion and dehydrogenation process of
terminal olefins has been achieved with
CuBr as catalyst and di-tert-butyldiaziri-
dinone as nitrogen source (see scheme).
Various terminal olefins can be effective-
ly converted into imidazolin-2-ones in
good yields under mild conditions. This
reaction provides ready access to imida-
zolin-2-ones.
&
Copper Catalysis
Y. Zhu, Y. Shi*
&& – &&
CuI-Catalyzed Sequential Diamination
and Dehydrogenation of Terminal
Olefins: A Facile Approach to
Imidazolinones
Chem. Eur. J. 2014, 20, 1 – 5
www.chemeurj.org
5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ