Rh-N-heterocyclic carbene (NHC) complex-catalyzed addition of phenylboronie acid to N-sulfonyl and N-phosphinoyl aldimines

Article abstract of DOI:10.1248/cpb.56.973

Rh-N-heterocyclic carbene (NHC) complexes were generated in situ from imidazolium salts, [RhCl(cod)]₂ and t-BuOK in dioxane. In the presence of a catalytic amount of Rh-NHC complexes, the addition reaction of phenylboronic acid to N-sulfonylarylimines and N-phosphinyolarylimines gave the corresponding amines in high yields.

Full text of DOI:10.1248/cpb.56.973

July 2008
Chem. Pharm. Bull. 56(7) 973—976 (2008)
973
Rh–N-Heterocyclic Carbene (NHC) Complex-Catalyzed Addition of
Phenylboronic Acid to N-Sulfonyl and N-Phosphinoyl Aldimines
Abu Bakar MD., Yumiko SUZUKI,* and Masayuki SATO*
School of Pharmaceutical Sciences, University of Shizuoka; 52–1 Yada, Suruga-ku, Shizuoka 422–8526, Japan.
Received March 18, 2008; accepted April 22, 2008; published online May 1, 2008
Rh–N-heterocyclic carbene (NHC) complexes were generated in situ from imidazolium salts, [RhCl(cod)]2
and t-BuOK in dioxane. In the presence of a catalytic amount of Rh–NHC complexes, the addition reaction of
phenylboronic acid to N-sulfonylarylimines and N-phosphinyolarylimines gave the corresponding amines in high
yields.
Key words N-heterocyclic carbene; rhodium; phenylboronic acid; addition reaction; N-sulfonylarylimine; N-phosphinoyl-
arylimine
The synthesis, isolation, and characterization of stable N- tion of imines. The Rh–NHC complex was prepared from
heterocyclic carbenes (NHCs) first reported by Arduengo et [RhCl(cod)]2, 1,3-diadamantylimidazolium chloride 2a, and
al.1) in 1991, have attracted attention for the use of NHCs as t-BuOK; then, N-sulfonylphenylimine 1a38) and phenyl-
ancillary ligands for transition metal complexes. Due to their boronic acid were added to the mixture. The reaction in diox-
strong s-donating properties, NHCs can form metal com- ane at 70 °C for 5 h afforded N-sulfonyldiarylmethylamine 3a
plexes that have high stabilities toward heat, moisture, and in 91% yield (Table 1, entry 1). The reaction without 2a in
air, and they have higher catalytic abilities than their phos- dioxane afforded the desired product 3a in only 62% yield
phine counterparts.2—6) NHCs are now used as ligands for after 10 h at 70 °C (entry 2). These results showed and indi-
transition metals in many important chemical transforma- cated that the NHC ligand accelerated the addition reaction.
tions such as Pd-catalyzed coupling reactions,7) Ru-catalyz- The reaction in THF afforded 3a in 48% yield, whereas in
ed olefin metathesis,8) Rh-catalyzed hydrosilylations,9—11) toluene, the reaction was very sluggish and gave no adducts
and Cu-catalyzed conjugate addition reactions.12—14) More- (Table 1, entries 3—4). On the basis of these results, dioxane
over, NHCs have attracted considerable attention as orga- was used as a solvent in the later reactions.
nocatalysts in several reactions such as benzoin condensa-
tion,15—20) Stetter reaction,21—23) transesterification/acylation carried out using imidazolium salts with mesityl substituent
reactions,24,25) and nucleophilic substitution reactions.26—28)
2b, triazolium salt 2c, and thiazolium salt 2d as ligand pre-
The addition reactions of phenylboronic acid to 1a were
In our study on the use of NHCs as ligands in organic cursors. Using imidazolium salt 2b and triazolium salt 2c,
transformations, we have recently reported the addition of di- the addition product was isolated in high yields (Table 2, en-
ethylzinc to N-sulfonylarylimines catalyzed by Cu–NHC tries 1 and 2). In the case of thiazolium salt 2d, only a small
complexes,29) where NHCs exhibit a strong ligand accelera- amount of addition product was obtained (Table 2, entry 3).
tion effect (LAE). This finding has prompted us to inves- From these results, it was found that triazolium salt 2c also
tigate the applicability of a similar methodology to the functioned as a potential ligand precursor.
Rh–NHC complex-catalyzed addition of phenylboronic acid
to imines.
Various N-sulfonylarylimines 1b—h were subjected to the
Rh–NHC complex-catalyzed addition reaction with phenyl-
The addition reaction of organometallic reagents to imines boronic acid. The substituted phenylimines with both elec-
is one of the most efficient procedures for the synthesis of di- tron-donating and electron-withdrawing groups, 1b—f, re-
arylmethylamines, which are important subunits of biologi- acted readily with phenylboronic acid in the presence of a
cally significant compounds.30—33) Despite many studies on
the Rh-phosphine complex-catalyzed addition of arylboronic Table 1. Arylation of N-Sulfonylphenylimine 1a Using Rh–NHC Com-
acids to imines,34,35) there is only one study, i.e., that by
plex
Charette and coworkers, in which the Rh–NHC complex is
used.36) Here, we report our results on the addition of aryl-
boronic acid to both N-sulfonylarylimines and N-phosphi-
noylarylimines by using a catalytic amount of Rh–NHC com-
plexes.
Results and Discussion
In the study by Charette and coworkers, the Rh–NHC
complex was prepared in situ using the NHC-transfer reagent
Ag–NHC and used as a catalyst in the arylation of p-
methylphenyl-N-phosphinoylimine with phenylboronic
acid.36) They showed only one reaction example. We exam-
ined the catalytic ability of the Rh–NHC complex generated
in situ37) from azolium salts and [RhCl(cod)]2 for the aryla-
Entry
Solvent
Time (h)
Yield (%)a)
1
Dioxane
Dioxane
THF
5
10
5
91
62
48
2b)
3
4
Toluene
8
No reaction
a) Isolated yield. b) Without imidazolium salt and base.
∗ To whom correspondence should be addressed. e-mail: msato@u-shizuoka-ken.ac.jp; suzuyumi@u-shizuoka-ken.ac.jp © 2008 Pharmaceutical Society of Japan

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Vol. 56, No. 7
Table 2. Arylation of N-Sulfonylphenylimine 1a Using Ligand Precursors Table 4. Arylation of N-Phosphinoylarylimines 4a—d
2b—d
Entry
1
Ar
Time (h)
5
Yield (%)
87
Entry
1
Azolium salt
Time (h)
5
Yield (%)
84
2
3
6
6
79
84
2
3
6
6
88
Trace
4
6
73
Table 3. Arylation of Various N-Sulfonylarylimines 1b—h
for the addition of phenylboronic acid to N-sulfonylaryl-
imines were applied to the reaction of N-phosphinoylaryl-
imines, only imine hydrolysis was observed. To overcome this
problem, the addition reactions were carried out in the pres-
ence of activated, powdered MS 4A. As a result, the addition
reaction of phenylboronic acid using a catalytic amount of
the Rh–NHC complex was successfully applied to the aryla-
tion of N-phosphinoylarylimines 4a—d39) that were derived
from benzaldehyde, 4-chlorobenzaldehyde, 4-methyl-
benzaldehyde, and 2-naphthaldehyde, affording the corre-
sponding addition products 5a—d in high yields (Table 4,
entries 1—4). In the study by Charette et al., 4c was used as
a substrate and the addition product 5c was obtained in 77%
yield after heating for 36 h at 50 °C.36) In our examples, ary-
lation gave better yields and we used the addition reaction in
a wide range of substrates.
Entry
1
Ar
Time (h)
6
Yield (%)
94
2
6
92
3
4
5
6
6
8
89
82
85
Conclusion
In conclusion, we have demonstrated a very efficient pro-
cedure for the addition of phenylboronic acid to both N-sul-
fonylarylimines and N-phosphinoylarylimines. The reaction
rate is higher than that in the study by Charette and cowork-
ers, in which the Rh–NHC complex is used as a catalyst.36)
The use of a catalytic amount of the Rh–NHC complex en-
ables us to synthesize diarylmethylamines in high yields. In
our laboratory, further investigations are in progress for de-
veloping an asymmetric version of this addition reaction.
6
7
6
5
97
89
Experimental
General Melting points were determined using the Yazawa micromelt-
catalytic amount of the Rh–NHC complex to give the corre-
sponding amines in high yields (Table 3, entries 1—5).
Bulky N-sulfonylaryl imines (1-naphthylimine 1g and 2-
trimethylsilylphenylimine 1h) were also phenylated with
phenylboronic acid, affording the corresponding amines in
high yields (Table 3, entries 6 and 7).
1
ing point apparatus without correction. H-NMR (500 MHz) and 13C-NMR
(126 MHz) spectra were recorded on a JEOL ECA-500 NMR spectrometer.
IR spectra were recorded on a Shimadzu IRPrestige-21. FAB-MS spectra
were recorded on a JEOL MStation JMS-700 mass spectrometer using m-ni-
trobenzyl alcohol as a matrix. Column chromatography was carried out with
silica gel 60 N (spherical, acidic; Kanto Chemical Co., Inc.).
General Procedure for the Preparation of N-Sulfonamides 3a—h To
a stirring suspension of azolium salt (4 mol%) and [RhCl(cod)]2 (3.9 mg,
Next, this procedure was applied to the other substrates,
i.e., N-phosphinoylarylimines. When the optimal conditions 4 mol%) in 1 ml dioxane, 1 M t-BuOK/THF (8 ml, 4 mol%) was added under

July 2008
975
argon atmosphere. The mixture was stirred at room temperature for 30 min. in 1 ml dioxane were successively added dropwise to the mixture. Activated
Then, the solution of phenylboronic acid (36.6 mg, 0.3 mmol) in 1 ml diox- MS 4A (powder) was added to this mixture. After stirring at 70 °C for the
ane and the solution of N-sulfonylarylimines 1a—h (0.2 mmol) in 1 ml diox- indicated time, the mixture was filtered through a pad of Celite 545 and the
ane were successively added dropwise to the mixture. After stirring at 70 °C celite cake was washed with CH2Cl2. H2O was added to this mixture; the
for the indicated time, the mixture was poured into H2O and extracted with mixture was then extracted with CH2Cl2 and washed with brine. The CH2Cl2
CH2Cl2. The organic layer was washed with brine, dried over MgSO4, and layer was dried over MgSO4 and concentrated. The residue was purified by
concentrated. The residue was purified by column chromatography (n- column chromatography (ethyl acetate) to afford the addition products 5a—
hexane/ethyl acetateꢀ3 : 1) to afford the addition products 3a—h.
d.
N-(Diphenylmethyl)-4-methylbenzenesulfonamide40) (3a): Colorless pow-
P,P-Diphenyl-N-(diphenylmethyl)phosphinic Amide42) (5a): Colorless
der (recrystallized from n-hexane/CH2Cl2), 91%, mp 131—133 °C; IR needles (recrystallized from n-hexane/CH2Cl2), 87%, mp 187—189 °C; IR
(ATR) cmꢁ1: 3234, 1317, 1157. 1H-NMR (CDCl3) d: 2.37 (3H, s), 5.25 (1H, (ATR) cmꢁ1: 3207, 1182. 1H-NMR (CDCl3) d: 3.64 (1H, dd, Jꢀ10.0,
d, Jꢀ7.5 Hz), 5.56 (1H, d, Jꢀ7.5 Hz), 7.07—7.13 (6H, m), 7.18—7.22 (6H, 7.0 Hz), 5.45 (1H, t, Jꢀ11.0 Hz), 7.21—7.31 (10H, m), 7.35—7.38 (4H, m),
m), 7.55 (2H, d, Jꢀ8.0 Hz). 13C-NMR (CDCl3) d: 21.6, 61.4, 127.3, 127.5, 7.46 (2H, td, Jꢀ7.5, 1.0 Hz), 7.81—7.85 (4H, m). 13C-NMR (CDCl3) d:
127.7, 128.6, 129.5, 137.4, 140.6, 143.3. MS (FAB) m/z 338 (Mꢂ1).
58.6, 127.3, 127.7, 128.5, 128.6, 132.0 (d, Jꢀ2.6 Hz), 132.3 (d, Jꢀ
N-(4-Chloro-a-phenylbenzyl)-4-methylbenzenesulfonamide40) (3b): Col- 130.0 Hz), 132.4 (d, Jꢀ9.5 Hz), 132.8, 143.4 (d, Jꢀ10.2 Hz). MS (FAB) m/z
orless solid (recrystallized from n-hexane/CH2Cl2), 94%, mp 115—117 °C; 384 (Mꢂ1).
1
IR (ATR) cmꢁ1: 3234, 1317, 1157. H-NMR (CDCl3) d: 2.39 (3H, s), 5.17
P,P-Diphenyl-N-(4-chloro-a-phenylbenzyl)phosphinic Amide34) (5b):
(1H, d, Jꢀ7.0 Hz), 7.03—7.06 (4H, m), 7.14 (2H, d, Jꢀ8.0 Hz), 7.17 (2H, d, Colorless crystalline powder (recrystallized from n-hexane/CH2Cl2), 79%,
1
Jꢀ8.5 Hz),7.13—7.18 (4H, m), 7.19—7.22 (3H, m), 7.54 (2H, d, Jꢀ8.0 Hz).
mp 165—167 °C; IR (ATR) cmꢁ1: 3117, 1196. H-NMR (CDCl3) d: 3.65
13C-NMR (CDCl3) d: 21.6, 60.8, 127.3, 127.4, 128.0, 128.7, 128.8, 128.9, (1H, dd, Jꢀ10.5, 7.0 Hz), 5.41 (1H, t, Jꢀ10.5 Hz), 7.19—7.25 (7H, m), 7.30
129.5, 133.5, 137.3, 139.1, 140.2, 143.5. MS (FAB) m/z 372 (Mꢂ1).
(2H, t, Jꢀ8.0 Hz), 7.35—7.39 (4H, m), 7.46 (2H, td, Jꢀ7.5, 1.0 Hz), 7.78—
N-(2-Chloro-a-phenylbenzyl)-4-methylbenzenesulfonamide40) (3c): Col- 7.83 (4H, m). 13C-NMR (CDCl3) d: 58.1, 127.6, 128.5, 128.6, 128.7, 128.7,
orless needles, (recrystallized from n-hexane/CH2Cl2), 92%, mp 168— 129.1, 132.0 (d, Jꢀ130 Hz), 132.2 (d, Jꢀ130 Hz), 132.3 (d, Jꢀ9.5 Hz),
1
170 °C; IR (ATR) cmꢁ1: 3323, 1333, 1153. H-NMR (CDCl3) d: 2.37 (3H, 132.4 (d, Jꢀ9.5 Hz), 133.1, 141.9 (d, Jꢀ4.9 Hz), 142.9 (d, Jꢀ5.2 Hz). MS
s), 5.30 (1H, d, Jꢀ7.0 Hz), 5.90 (1H, d, Jꢀ7.0 Hz), 7.05—7.07 (2H, m),
(FAB) m/z 418 (Mꢂ1).
7.13—7.17 (4H, m), 7.21—7.24 (4H, m), 7.33—7.35 (1H, m), 7.61 (2H, d,
P,P-Diphenyl-N-(4-methyl-a-phenylbenzyl)phosphinic Amide35) (5c):
Jꢀ8.5 Hz). 13C-NMR (CDCl3) d: 21.6, 58.7, 127.0, 127.3, 127.4, 128.0, Colorless needles (recrystallized from n-hexane/CH2Cl2), 84%, mp 174—
1
128.8, 128.9, 129.5, 129.5, 130.0, 132.9, 137.0, 137.6, 139.4, 143.5. MS
176 °C; IR (ATR) cmꢁ1: 3215, 1435, 1180. H-NMR (CDCl3) d: 2.31 (3H,
(FAB) m/z 372 (Mꢂ1).
s), 3.64 (1H, dd, Jꢀ10.5, 7.0 Hz), 5.41 (1H, t, Jꢀ10.5 Hz), 7.09 (2H, d,
N-(4-Methoxy-a-phenylbenzyl)-4-methylbenzenesulfonamide40) (3d): Jꢀ8.0 Hz), 7.14 (2H, d, Jꢀ8.0 Hz), 7.20—7.30 (5H, m), 7.34—7.39 (4H,
Colorless solid (recrystallized from n-hexane/CH2Cl2), 89%, mp 136— m), 7.43—7.48 (2H, m), 7.80—7.85 (4H, m). 13C-NMR (CDCl3) d: 21.2,
1
139 °C; IR (ATR) cmꢁ1: 3234, 1319, 1157. H-NMR (CDCl3) d: 2.37 (3H, 58.4, 127.2, 127.6, 127.6, 128.5, 128.5, 129.3, 131.8 (d, Jꢀ130.0 Hz), 132.0,
s), 3.74 (3H, s), 5.28 (1H, d, Jꢀ7.5 Hz), 5.51 (1H, d, Jꢀ7.5 Hz), 6.71 (2H, d, 132.4 (d, Jꢀ9.5 Hz), 132.8 (d, Jꢀ130.0 Hz), 137.0, 140.5 (d, Jꢀ9.0 Hz),
Jꢀ8.5 Hz), 6.82 (2H, d, Jꢀ8.5 Hz), 7.09—7.13 (4H, m), 7.17—7.21 (3H, 143.0 (d, Jꢀ9.0 Hz). MS (FAB) m/z 398 (Mꢂ1).
m), 7.54 (2H, d, Jꢀ8.5 Hz). 13C-NMR (CDCl3) d: 21.6, 55.4, 60.9, 114.0,
127.3, 127.4, 127.5, 128.6, 128.7, 129.4, 132.9, 137.5, 140.8, 143.2, 159.0.
N-(2-Methoxy-a-phenylbenzyl)-4-methylbenzenesulfonamide40) (3e):
P,P-Diphenyl-N-[(2-naphthyl)phenylmethyl]phosphinic Amide (5d): Col-
orless granules (recrystallized from n-hexane/CH2Cl2), 73%, mp 192—
1
194 °C; IR (ATR) cmꢁ1: 3117, 1506, 1194. H-NMR (CDCl3) d: 3.79 (1H,
Colorless plates (recrystallized from n-hexane/CH2Cl2), 82%, mp 124— dd, Jꢀ10.0, 7.0 Hz), 5.62 (1H, t, Jꢀ11.0 Hz), 7.23—7.48 (13H, m), 7.64
1
126 °C; IR (ATR) cmꢁ1: 3302, 1321, 1151. H-NMR (CDCl3) d: 2.31 (3H, (1H, s), 7.73—7.87 (8H, m). 13C-NMR (CDCl3) d: 58.8, 125.9, 126.1,
s), 3.58 (3H, s), 5.64 (1H, d, Jꢀ9.0 Hz), 5.78 (1H, d, Jꢀ9.0 Hz), 6.67 (1H, d, 126.3, 127.4, 127.7, 127.8, 128.2, 128.5, 128.5, 128.6, 128.6, 128.6, 131.7
Jꢀ8.6 Hz), 6.77 (1H, t, Jꢀ7.5 Hz), 6.97 (1H, dd, Jꢀ7.5, 2.0 Hz), 7.04 (2H,
d, Jꢀ8.0 Hz), 7.13—7.23 (6H, m), 7.50 (2H, d, Jꢀ8.0 Hz). 13C-NMR
(CDCl3) d: 21.5, 55.3, 59.1, 111.2, 120.7, 126.9, 127.1, 127.2, 127.7, 128.2,
129.0, 129.1, 129.7, 137.6, 140.6, 142.9, 156.4.
(d, Jꢀ130.0 Hz), 132.0, 132.3 (d, Jꢀ9.0 Hz), 132.4, 132.4, 132.5 (d,
Jꢀ9.0 Hz), 132.9 (d, Jꢀ130.0 Hz), 133.2, 140.7 (d, Jꢀ5.8 Hz), 143.3 (d,
Jꢀ5.3 Hz). HR-MS (FAB) Calcd for C29H25NPO (Mꢂ): 434.1674, Found:
434.1715.
N-[(4-Methyl-a-phenylbenzyl)-4-methylbenzenesulfonamide33) (3f): Col-
orless needles (recrystallized from n-hexane/CH2Cl2), 85%, mp 117— References
1
119 °C; IR (ATR) cmꢁ1: 3253, 1317, 1161. H-NMR (CDCl3) d: 2.27 (3H,
s), 2.38 (3H, s), 5.07 (1H, d, Jꢀ7.0 Hz), 5.51 (1H, d, Jꢀ7.0 Hz), 6.96 (2H, d,
Jꢀ8.0 Hz), 7.01 (2H, d, Jꢀ8.0 Hz), 7.10 (2H, dd, Jꢀ7.5, 2.0 Hz), 7.13 (2H,
d, Jꢀ7.5 Hz), 7.17—7.21 (3H, m), 7.55 (2H, d, Jꢀ8.0 Hz). 13C-NMR
(CDCl3) d: 21.1, 21.6, 61.2, 127.3, 127.4, 127.4, 127.6, 128.6, 129.3, 129.4,
137.4, 137.5, 137.7, 140.8, 143.2.
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Vol. 56, No. 7
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