Organic Letters
Letter
coordinated Ni(CO)4 or nonreactive nickel complexes Ni-
(CO)3L, which will limit the reactivity of the oxidation step.17
In this aspect, the use of CO surrogates would offer an ideal
choice. Here, it is also important to mention that Zhang and
co-workers were recently able to apply nickel-based catalysts
for the carbonylative coupling of alkyl halides with arylboronic
acids under 1 atm of CO.17f,g With our continuous interest in
carbonylation reactions, we herein disclose a nickel-catalyzed
thiocarbonylation of arylboronic acid with sulfonyl chlorides,
employing Mo(CO)6 as the CO surrogate and reductant
(Scheme 1, eq e).
Initially, phenylboronic acid and p-toluenesulfonyl chloride
were chosen as the model substrates to evaluate the feasibility
of this thiocarbonylation reaction. To our delight, with K2CO3
as the base and Mo(CO)6 as the CO source and reductant,
assisted by H2O in NMP at 120 °C, the desired thioester 3aa
was obtained in 35% yield in the presence of Ni(OTf)2 using
dtbbpy as the ligand (Table 1, entry 1). Subsequently, various
nickel catalysts were studied, and a slightly lower yield was
observed with NiI2 (Table 1, entry 2). The yield of 3aa
dropped with the other tested nickel catalysts, including NiCl2,
NiBr2, Ni(acac)2, and Ni(COD)2 (Table 1, entries 3−6). We
then studied the effect of ligands, and unfortunately, reduced
yields were obtained with these ligands (Table 1, entries 7−
10). Afterward, different bases involving DBU, DiPEA,
KHCO3, and K3PO4 were investigated, and no target product
could be detected (Table 1, entries 11−14). In addition, by
adding 10 mol % of TMSCl as the additive, the yield of 3aa
increased to 38% (Table 1, entry 15). Yields of 42−53% of the
desired thioester can be obtained with TMSI, NaI, KI, or ZnI2
as the additive (Table 1, entries 16−19). When 20 mol % of
ZnI2 was used, 3aa was observed in 65% yield (Table 1, entry
20). Furthermore, increasing the loading of Ni(OTf)2 to 20
mol %, the yield of the expected thioester was improved to
76% (Table 1, entry 21). Notably, no desired product could be
detected in the absence of nickel or ligand (Table 1, entries
22−23).
With the optimal reaction conditions in hand, we
investigated the substrate scope of arylboronic acids for this
thiocarbonylative transformation (Scheme 2). The target
a
Scheme 2. Substrate Scope of Arylboronic Acids
a
Table 1. Screening of Reaction Conditions
entry
[Ni]
ligand
base
additive
yield (%)
1
2
3
4
5
6
7
8
Ni(OTf)2
NiI2
NiCl2
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
1,10-phen
bpy
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
KHCO3
K3PO4
DBU
DiPEA
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
35
32
24
22
21
22
10
trace
17
18
n.d.
n.d.
n.d.
n.d.
38
44
42
49
53
65
76
0
NiBr2
Ni(acac)2
Ni(COD)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
Ni(OTf)2
/
9
PPh3
a
10
11
12
13
14
15
16
17
18
19
DPEphos
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
dtbbpy
/
Reaction conditions: arylboronic acid (0.5 mmol), p-toluenesulfonyl
chloride (0.75 mmol), Ni(OTf)2 (20 mol %), dtbbpy (20 mol %),
ZnI2 (40 mol %), Mo(CO)6 (1.0 equiv), K2CO3 (1.5 equiv), H2O
(0.5 equiv), NMP (2 mL), 120 °C, 16 h, isolated yield.
TMSCl
TMSI
NaI
products were obtained in good to excellent yields with
arylboronic acids bearing electron-donating groups such as
methyl, ethyl, tert-butyl, and methoxy groups (3ba−3ea).
Arylboronic acids with weak electron-withdrawing groups,
including fluoro and chloro substituents, and the desired
products were isolated in 76% and 60% yields, respectively, as
well (3fa−3ga). However, the reactions failed when arylbor-
onic acids bearing strong electron-deficient substituents, such
as CN, and CF3, were tested. Only protodeboronation
products were detected. Additionally, substrates with a 2-
naphthalene moiety were compatible to provide the corre-
sponding thioester in high yield (3ha). Moreover, heteroaryl
boronic acids were also tolerated well in this thiocarbonylation
reaction, and furan-2- and 3-ylboronic acids reacted with p-
toluenesulfonyl chloride successfully to afford the expected
products in 55% and 60% yields (3ia−3ja). Notably, thiophen-
3-ylboronic acid could work very well to give the final product
KI
ZnI2
ZnI2
ZnI2
ZnI2
ZnI2
b
20
21
22
23
c
c
c
dtbbpy
0
a
Reaction conditions: phenylboronic acid (0.5 mmol), p-toluenesul-
fonyl chloride (0.75 mmol), catalyst (10 mol %), ligand (20 mol % for
monodentate ligands, 10 mol % for bidentate ligand), Mo(CO)6 (1.0
equiv), base (1.5 equiv), additive (10 mol %), H2O (0.5 equiv), NMP
(2 mL), 120 °C, 16 h. GC yield, with dodecane as the internal
standard. Additive (20 mol %). Catalyst (20 mol %), ligand (20 mol
%), additive (40 mol %). dtbbpy: 4,4′-di-tert-butyl-2,2′-dipyridyl. bpy:
2,2′-bipyridine. 1,10-phen: 1 10-phenanthroline.
b
c
B
Org. Lett. XXXX, XXX, XXX−XXX