Carbon-nitrogen bond formation between allyl silyl ether and hydrazide promoted by mercuric triflate catalyst

Article abstract of DOI:10.1055/s-0031-1290758

An efficient method for carbon-nitrogen bond formation between ally silyl ethers and N,N-acyltosylhydrazine was developed under very mild conditions using 2 mol% of mercuric triflate [Hg(OTf) as a catalyst. This method does not require the use of any ligand system or supplementary additives and is applicable to the preparation of various N-allylhydrazides with good to excellent yields. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0031-1290758

LETTER
▌1069
Letter
Carbon–Nitrogen Bond Formation between Allyl Silyl Ether and Hydrazide
Promoted by Mercuric Triflate Catalyst
Carbon–Nitrogen Bond Formation between Allyl Silyl Ether and Hydrazide
Hirofumi Yamamoto,*a Naoto Yamasaki,a Shingo Yoshidome,a Ikuo Sasaki,a Kosuke Namba,b Hiroshi Imagawa,a
Mugio Nishizawaa
a
Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho, Tokushima 770-8514, Japan
Fax +81(88)6553051; E-mail: hirofumi@ph.bunri-u.ac.jp
b
Division of Chemistry, Graduate School of Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan
Received: 24.01.2012; Accepted after revision: 14.02.2012
ing study of hydrazines being employed as the nucleo-
Abstract: An efficient method for carbon–nitrogen bond formation
phile for Tuji–Trost-type reactions was performed by Lee
between ally silyl ethers and N,N-acyltosylhydrazine was devel-
and co-workers in 2005.7 This reaction of allylic carbon-
ates with t-Boc-protected hydrazine proceeded at room
oped under very mild conditions using 2 mol% of mercuric triflate
[Hg(OTf)2] as a catalyst. This method does not require the use of
any ligand system or supplementary additives and is applicable to temperature in the presence of a catalytic amount of
the preparation of various N-allylhydrazides with good to excellent
yields.
[Ir(cod)Cl]2 complex and pyridine ligand; however, the
additions of Et2Zn (0.25–0.5 equiv)8 and NH4I (1 equiv)9
Key words: allylation, amination, hydrazine, silyl ether, mercury
are essential to induce the reaction. Herein is proposed a
new and simple protocol for the catalytic synthesis of al-
lylhydrazine derivatives.
Tuji–Trost-type amination of allyl halides, carbonates,
carboxylates, or phosphonates with amine nucleophiles
has served as a pivotal reaction in a number of syntheses
of nitrogen-containing natural products and pharmaceuti-
cals.1 Indeed, a variety of allylamine units have been effi-
Namba, Tanino, and co-workers most recently reported
the efficient preparation of N,N-acyltosylhydrazine (4) us-
ing a catalytic amount of 4-aminopyridine.10 Although
N,N-diprotected hydrazines including 4 have almost nev-
er been employed as key synthons for organic synthesis,11
the structure of 4 has a clear advantage in achieving selec-
tive allylation at only one of two nitrogens. Moreover, 4 is
expected to function as a mild nitrogen nucleophile as a
result of having two electron-withdrawing groups on the
same nitrogen atom. Thus we hypothesized that 4 would
be a suitable nitrogen source for a Hg(OTf)2-catalyzed
carbon–nitrogen bond-forming reaction.
ciently constructed using
a catalytic amount of
palladium,2 iridium,3 or some other reagent.4 Recently, we
found remarkable catalytic activity in Hg(OTf)2 for the al-
lylic amination of allyl alcohols and ‘soft’ nitrogen nu-
cleophiles such as sulfamates or sulfonamides.5 For
example, the reaction of 2-cyclo-1-hexen-1-ol (1a) with
methyl sulfamate (2) using 2 mol% of Hg(OTf)2 affords 3
in excellent yield at room temperature (Scheme 1).5b
Initially, the reaction of commercially available 1a with 4
was examined, using 2 mol% of Hg(OTf)2 in CH2Cl2 (Ta-
ble 1, entry 1). However, in contrast to the allylic amina-
tion with methyl sulfamate, the reaction conditions only
gave a small quantity of the desired product 5, along with
dimerized 6 as a byproduct after 48 hours. MeCN and tol-
uene were also poor solvents, affording 5 in 10% and 15%
yield, respectively. A better result was obtained by
switching to MeNO2, but the yield was still only 25% (Ta-
ble 1, entry 4). Thus, other conditions using allyl alcohol
derivatives 1b–h as allyl sources were examined. When
allyl acetate 1b and carbonate 1c were used, no reaction
resulted upon addition of 4 (Table 1, entries 5 and 6).
Methyl ether 1d was also ineffective at inducing the reac-
tion, giving only a trace amount of 5 after 24 hours (Table
1, entry 7). In contrast, interestingly, trimethylsilyl (TMS)
ether 1e showed remarkable reactivity, giving rise to the
desired adduct in 50% yield in six hours (Table 1, entry 8).
However, cleavage of the siloxy group in 1e took place si-
multaneously under the reaction conditions, confirming
the tendency of some silyl ethers to find a more ideal leav-
ing group. For tert-butyldimethylsilyl (TBS) ether 1f, the
reactivity was slightly increased compared to that of 1e,
Hg(OTf)2
(2 mol%)
H
O
O
N
OH
OMe
S
S
+
OMe
H2N
O
O
CH2Cl2, r.t.
1a
2
3 90%
Scheme 1 Hg(OTf)2-catalyzed allylic amination
As part of our ongoing studies of carbon–nitrogen bond-
forming reactions, we have been exploring the use of hy-
drazines instead of methyl sulfamate. Although the nitro-
gen–nitrogen linkage of hydrazines is an important
structural unit in organic chemistry,6 there have been only
a few examples of Tuji–Trost-type reactions using hydra-
zines as the nitrogen nucleophile: For the synthesis of al-
kyl- or allyl-substituted hydrazine derivatives, classical
SN2-type reaction using halogenated compounds under
severe conditions has traditionally been used.6a A pioneer-
SYNLETT 204012, 237, 1069–1073
Advanced online publication: 05.04.2012
DOI: 10.1055/s-0031-1290758; Art ID: ST-2012-U0073-L
© Georg Thieme Verlag Stuttgart · New York
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6

1070
H. Yamamoto et al.
LETTER
tallography. Figure 1 illustrates the molecular structure of
5,14 which was crystallized from a mixture of hexane and
ethyl acetate (3:1) at room temperature.
Table 1 Optimization of the Hg(OTf)2-Catalyzed Amination of 1
with 4
H
OR
Ac
N
O
Ts
N
catalyst
(2 mol%)
N
+
H2N
+
Ts
Ac
r.t.
5
1a–h
4
6
Entry Catalyst
Solvent
1 R
Time Yield of 5
(h)
(%)a
12/22b
10/20b
25/38b
25/25b
0
1
2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
Hg(OTf)2
CH2Cl2
MeCN
PhMe
1a H
1a H
1a H
48
48
48
8
Figure 1 ORTEP plot of the molecular structure 5
3
4
MeNO2 1a H
MeNO2 1b Ac
Next, an attempt was made to find an effective palladium
catalyst leading to 5, since the hydrazide 4 is thought to re-
act with a π-allylpalladium intermediate (Table 1, entries
12–14). However, reaction with 4 was unsuccessful under
the general allylic amination reaction conditions using al-
lyl carbonate derivatives,2a and the majority of 1c decom-
posed after 24 hours. After several other attempts using
phenyl mercuric triflate (PhHgOTf),15 gold catalysts,16
and In(OTf)3,17 all known to have reactivity similar to
Hg(OTf)2, the combination of Hg(OTf)2 and the TBDPS
group was found to be the most suitable for the carbon–
nitrogen bond formation using 4 (Table 1, entries 15–20).
5
0.5
6
MeNO2 1c CO2Me
MeNO2 1d Me
MeNO2 1e TMS
MeNO2 1f TBS
MeNO2 1g TIPS
24
24
6
0
7
trace
50
8
9
6
52
10
11
6
62
88/82c
0
MeNO2 1h TBDPS
4
12d
13d
14d
15e
16
Pd(PPh3)2Cl2
[Pd(C3H5)Cl]2
CH2Cl2
CH2Cl2
1c CO2Me
1c CO2Me
1c CO2Me
24
24
24
A plausible mechanism for the Hg(OTf)2-catalyzed reac-
tion of 1h with 4 is depicted in Scheme 2. Nucleophilic at-
tack of 4 is promoted by complexation of 1h with
Hg(OTf)2, producing the organomercuric intermediate 9.
Then, incidental protonation of the siloxy moiety in 9 by
in situ generated TfOH leads to product 5 via demercura-
tion step 10. Although the exact effect of TBDPS group is
unclear, it is likely that its bulkiness enhances the leaving
ability of siloxy group. However, more detailed investiga-
tion is required for full elucidation of the role.
0
Pd2(dba)3CHCl3 CH2Cl2
0
PhHgOTf
AuCl
MeNO2 1h TBDPS 24
MeNO2 1h TBDPS 24
MeNO2 1h TBDPS 24
MeNO2 1h TBDPS 24
MeNO2 1h TBDPS 24
MeNO2 1h TBDPS 24
trace
42
17f
18
19
20
PPh3AuCl
AuCl3
57
trace
23
In(OTf)3
HOTf
1h
Si-OH
+
5
Hg(OTf)2
trace
–OTf
a Yield was determined by comparison of the 1H NMR integration of
the crude mixture to an internal standard (CH2Br2).
b Yield of homodimer 6.
Hg(OTf)2
TfOHg
O+
H
H
O
Ac
N
Si
N
c Yield of isolated product 5.
Si
d Reaction carried out using Ph3P (4 mol%) at reflux.
e Catalyst was prepared from PhHgOAc (2 mol%) and HOTf (2
mol%).
Ts
7
10
4
f Reaction carried out using AgOTf (2 mol%).
HOTf
–OTf
+N
giving 5 in 52% yield (Table 1, entry 9). Triisopropylsilyl
(TIPS) ether 1g was even more suitable to the catalytic
system, as 5 was obtained in 62% yield (Table 1, entry
10). Among the siloxy groups evaluated, tert-butyldiphe-
nylsilyl (TBDPS) ether 1h showed the best reactivity, af-
fording 5 in 88% yield after four hours (Table 1, entry
11).12,13 The isolated product 5 was characterized by NMR
and IR spectroscopy, mass spectrometry, and X-ray crys-
TfOHg
TfOHg
H
N
H2
Ac
O
Ac
O
Si
N
Si
N
Ts
Ts
8
9
Si = TBDPS
Scheme 2 Proposed mechanism of Hg(OTf)2-catalyzed reaction of
1h with 4
Synlett 2012, 23, 1069–1073
© Georg Thieme Verlag Stuttgart · New York

LETTER
Carbon–Nitrogen Bond Formation between Allyl Silyl Ether and Hydrazide
1071
As shown in Table 2, this procedure is applicable to the re- 5 and 6). This result is similar to that of the Hg(OTf)2-cat-
action of both cyclic and acyclic ethers. In the case of the alyzed allylic amination with methyl sulfamate,5b and sug-
2-cyclopentenyl derivative 11 (Table 2, entry 1), the reac- gests that an equilibrium between 20 and 22 exists under
tivity was dramatically increased compared to that of 1h, the reaction conditions. Therefore, the formation of the
as the reaction was induced even at 0 °C. Acyclic 13, 15, more stable conjugated isomer 20 should prevail over the
and 17 also gave the corresponding desired adducts 14, formation of 22. The reaction of phenyl-substituted 23
16, and 18 in acceptable yields (Table 2, entries 2–4). The also proceeded regioselectively to afford 24 in good yield
conjugated diene 19 and nonconjugated 21 afforded the (Table 2, entry 7). Even with 25 and 27 as the unsymmet-
same conjugated product 20 as a single E-isomer, as de- rical substrates, single products 26 and 28 were formed in
tected by X-ray crystal structure analysis (Table 2, entries excellent yields, respectively (Table 2, entries 8 and 9).
Table 2 Hg(OTf)2-Catalyzed Allylic Amination of Allyl Silyl Ethers with 4
Yield (%)b
78
Entry
Substrate
Adduct
Time (min)
30
H
OTBDPS
N
Ac
1
11
12
N
Ts
Ts
OTBDPS
N
HN
Ac
2
3
13
15
14
16
180
60
76
70
Ts
OTBDPS
N
HN
Ac
Bu
Bu
Bu
Bu
Ts
N
OTBDPS
HN
HN
Ac
4
17
18
60
84
Ts
N
OTBDPS
Ac
5
6
19
21
20
22
20
30
85
83
Ts
N
OTBDPS
HN
Ac
Ts
N
OTBDPS
HN
Ac
7
8
9
23
25
27
24
26
28
30
60
10
86
88
88
Ts
OTBDPS
N
HN
Ac
Ts
OTBDPS
N
HN
Ac
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 1069–1073

1072
H. Yamamoto et al.
LETTER
Yield (%)b
92
Table 2 Hg(OTf)2-Catalyzed Allylic Amination of Allyl Silyl Ethers with 4 (continued)
Entry
10
Substrate
Adduct
Time (min)
Ts
N
OTBDPS
HN
Ac
29
30
10
Ts
N
OTBDPS
HN
Ac
11
31
32
10
63
EtOOC
EtOOC
a Except for entries 1, 10 and 11, reactions were carried out with Hg(OTf)2 (2 mol%) in MeNO2 at r.t.
b Yield of isolated product.
c Reaction was carried out at 0 °C.
d Yield of isolated conjugated product 20.
e Reaction was carried out at reflux.
f Reaction was carried out using Hg(OTf)2 (5 mol%) at reflux.
The reactions using diastereomerically pure cis-5-substi- In summary, a Hg(OTf)2-catalyzed carbon–nitrogen
tuted 29 and 31 were sluggish, and required reflux to bond-forming reaction between allyl silyl ethers and N,N-
reach completion within a reasonable reaction time (Table acyltosylhydrazine has been developed. In many cases,
2, entries 10 and 11). However, thermodynamically stable the reaction can be performed with as little as 2 mol% of
diastereoisomers 30 and 32 were obtained in good to ex- catalyst at room temperature, giving excellent yields. To
cellent yields within 10 minutes under reflux.
the best of our knowledge, the present method is the first
example employing siloxy functionality as a leaving
group for allylic amination. Furthermore, the application
of N,N-acyltosylhydrazine highlights the utility of the re-
action. Thus, the present method constitutes a reasonable
alternative for the preparation of various hydrazine deriv-
atives.
The utility of the N,N-acyltosylhydrazine functionality is
demonstrated by the various divergent transformations
from product 5 (Scheme 3). Treatment with SmI2 in the
presence of tetramethylurea (TMU) gave 33 in 84% yield.
The selective deprotection of the acyl group also succeed-
ed upon using ten equivalents of NaHCO3 and 0.4 equiv-
alents of MeONa. Furthermore, conversion to the
hydrazone 36 was easily achieved via unstable intermedi-
ate 35 by treatment with K2CO3 in toluene. Moreover, cat-
alytic hydrogenation using Pd/C afforded 37
quantitatively, without disruption of the nitrogen–nitro-
gen linkage.
Acknowledgment
This study was financially supported by a Grant-in-Aid (Young Sci-
entists (B) and Senryaku-project) from MEXT (Ministry of Educa-
tion, Culture, Sports, Science, and Technology of the Japanese
Government).
H
H
N
Ac
Ac
SmI2
N
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.onmornifIatngonimSorfniturItagponiSutpor
N
N
H
TMU, MeOH
r.t., 10 min
Ts
5
33 84%
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N
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Scheme 3 Reactivity of N,N-acetyltosylhydrazine adduct 5
Synlett 2012, 23, 1069–1073
© Georg Thieme Verlag Stuttgart · New York

LETTER
Carbon–Nitrogen Bond Formation between Allyl Silyl Ether and Hydrazide
1073
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© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 1069–1073

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