W. Fan et al. / Tetrahedron 71 (2015) 4035e4038
4037
decarbonylation12e15 (eq 2). Finally, 1a-D or 1a reacted with addi-
tion 5 equiv H2O or D2O under standard conditions affording the
mixture of 3a (D/H¼5.5:4.5, D/H¼3.5:6.5, respectively). This ex-
periments were also in agreement with the forming NeRh or N]
Rh species.
With these results in hand, a possible mechanism was suggested
in Scheme 4. The initial oxidative addition process occurred to form
intermediate I,12e15 subsequently decarbonylation to form in-
termediates II or III,16 finally CeH activation to leaving H2 or Rh(I)
species to give 2a.16 However, Some of the results in Table 2, such as
2n and 2t, can not be explained by the proposed mechanism, which
might due to the big steric hindrance making the intermediate II or
III unstable.
J¼7.6 Hz, 1H), 2.55 (s, 3H); HRMS (EI) m/z calcd for C13H11N [M]þ:
181.0891, found: 181.0890.
4.2.3. 2c: 2-Chloro-9H-carbazole.7d (79%) mp 236e240 ꢀC; 1H NMR
(500 MHz, DMSO-d6): 11.45 (s, 1H), 8.10 (d, J¼8.4 Hz, 2H), 7.56 (d,
J¼2.0 Hz, 1H), 7.51 (td, J¼8.1, 0.7 Hz, 1H), 7.42 (m, 1H), 7.18 (m, 1H),
7.17 (dd, J¼8.4, 2.0 Hz, 1H); HRMS (EI) m/z calcd for C12H8ClN [M]þ:
201.0345, found: 201.0344.
4.2.4. 2d: 2-Nitro-9H-carbazole.7d (74%) mp 174e175 ꢀC; 1H NMR
(500 MHz,DMSO-d6):
d 8.38e8.35 (m, 2H), 8.28e8.26 (m, 1H),
8.05e8.03 (m, 1H), 7.64e7.62 (m, 1H), 7.55e7.53 (m, 1H), 7.30e7.27
(m, 1H); HRMS (EI) m/z calcd for C12H8N2O2 [M]þ: 212.0586, found:
212.0583.
4.2.5. 2e: 4-Methyl-9H-carbazole.7d (55%) mp 120e122 ꢀC; 1H NMR
Standard conditions
(500 MHz, CDCl3):
d
8.23 (d, J¼8.0 Hz, 1H), 8.02 (br s, 1H), 7.45e7.43
(m, 2H), 7.36e7.33 (m, 1H), 7.29e7.25 (m, 2H), 7.04 (dd, J¼7.0 Hz,
0.5 Hz, 1H), 2.94 (s, 3H); HRMS (EI) m/z calcd for C13H11N [M]þ:
181.0891, found: 181.0890.
NH
CHO
N
H
2a
1a
Rh(I)
4.2.6. 2f: 4-Chloro-9H-carbazole.7d (62%) mp 88e92 ꢀC; 1H NMR
(III)
Rh
(500 MHz, CDCl3):
J¼7.6 Hz, 1.0 Hz, 1H), 7.38e7.33 (m, 3H), 7.25e7.22 (m, 2H); HRMS
d
8.66 (d, J¼8.0 Hz, 1H), 7.92 (br s, 1H), 7.50 (dd,
N
H
H
II
(EI) m/z calcd for C12H8ClN [M]þ: 201.0345, found: 201.0346.
(III)
Rh
N
H
H
4.2.7. 2g: 3-Fluoro-9H-carbazole.7d (84%) mp 208e209 ꢀC; 1H NMR
O
Rh(III)
(500 MHz, CDCl3):
d
8.03 (d, J¼7.6 Hz, 2H), 7.72 (dd, J¼9.0 Hz, 2.5 Hz,
N
III
I
1H), 7.47e7.42 (m, 2H), 7.35 (dd, J¼9.0 Hz, 4.0 Hz,1H), 7.27e7.20 (m,
1H), 7.17 (dt, J¼9.0 Hz, 2.6 Hz, 1H); HRMS (EI) m/z calcd for C12H8NF
[M]þ: 185.0641, found: 185.0640.
Scheme 4. Proposed formation mechanism.
4.2.8. 2h: 3-Trifluoromethyl-9H-carbazole.7d (77%) mp 158e162 ꢀC;
1H NMR (500 MHz,DMSO-d6): 10.65 (s, 1H), 8.03 (s, 1H), 7.81 (d,
J¼9.4 Hz, 1H), 7.32 (d, J¼9.4 Hz, 1H), 7.27e7.18 (m, 2H), 7.14 (t,
J¼9.4 Hz, 1H), 6.85 (t, J¼9.4 Hz, 1H); HRMS (EI) m/z calcd for
3. Conclusions
In summary, we have developed a one-pot Rh(I)-catalyzed
synthesis of 9-H carbazoles via CeN bond cleavage by activation of
aldehyde CeH bonds. This direct CeH amination is suitable for
a broad range of substrates. The control experiments suggested
a possible decarbonylation mechanism. Further studies concerning
the detailed mechanism and the broader scope of substrates are
currently underway in our laboratory.
C
13H8NF3 [M]þ: 235.0609, found: 235.0610.
4.2.9. 2j: 3-Phenyl-9H-carbazole.17a (83%) mp; 1H NMR (CDCl3):
8.33 (t, J¼6.8 Hz, 1H), 8.17 (m, 1H), 8.10 (br s, 1H, NH), 7.75e7.71 (m,
2H), 7.70 (m, 1H), 7.55e7.46 (m, 5H), 7.38 (m, 1H), 7.28 (m, 1H);
HRMS (EIþ) m/z calcd for C18H13N [M]þ: 243.1048, found: 243.1045.
4. Experiment
4.1. General
4.2.10. 2k: 3-Methoyl-9H-carbazole.7d (87%) mp; 1H NMR (CDCl3):
8.06 (d, J¼7.0 Hz, 1H), 8.04 (br s, 1H, NH), 7.58 (d, J¼7.2 Hz, 1H),
7.42e7.41 (m, 2H), 7.35 (d, J¼9.8 Hz, 1H), 7.22 (m, 1H), 7.07 (dd,
J1¼7.2 Hz, J2¼3.0 Hz, 1H), 3.99 (s, 3H, OMe); HRMS (EIþ) m/z calcd
for C13H11NO [M]þ: 197.0841, found: 197.0840.
4.1.1. Procedure for synthesis of 2ae2t. A mixture of 1 (0.2 mmol),
[Rh(COD)OTf]2 (2 mol %) and Xantphos (3 mol %) in NMP (4 mL) was
stirred at 190 ꢀC under Ar atmosphere for 24 h. After the reaction
system was cooled to room temperature, saturated NH4Cl solution
(30 mL) and EtOAc (20 mL) were added. The combined organic
phases were dried over Na2SO4 and then concentrated to give crude
products. Further separation by column chromatography on silica
gel (eluant with EtOAc and n-hexane) gave the corresponding
products.
4.2.11. 2l: 1,3-Dichloro-9H-carbazole.17b (49%) mp; 1H NMR
(d6eacetone): 10.67 (br, 1H, NH), 8.19e8.14 (m, 2H), 7.60 (m, 1H),
7.53e7.47 (m, 2H), 7.25 (td, J1¼7.4 Hz, J2¼1.5 Hz, 1H); HRMS (EIþ) m/
z calcd for C12H7Cl2N [M]þ: 234.9956, found: 234.9958.
4.2.12. 2o:
Methyl
9H-carbazole-2-carboxylate.7d (65%)
mp
180e182 ꢀC; 1H NMR (500 MHz,DMSO-d6):
d
11.56 (s, 1H), 8.23 (d,
4.2. Characterization data
J¼8.2 Hz, 1H), 8.19 (d, J¼7.8 Hz, 1H), 8.14 (d, J¼2.8 Hz, 1H), 7.79 (dd,
J¼8.2, 1.4 Hz, 1H), 7.58 (d, J¼8.2 Hz, 1H), 7.45 (m, 1H), 7.20 (m, 1H),
3.90 (s, 3H); HRMS (EIþ) m/z calcd for C14H11NO2 [M]þ: 225.0790,
found: 225.0791.
4.2.1. 2a: 9H-Carbazole.6c (81%) mp 243e245 ꢀC; 1H NMR
(500 MHz, CDCl3):
7.45e7.40 (m, 4H), 7.27e7.24 (m, 2H); HRMS (EI) m/z calcd for
12H9N [M]þ: 167.0735, found: 167.0736.
d
8.11 (d, J¼7.8 Hz, 2H), 8.05 (br s, 1H, NH),
C
4.2.13. 2p: 2-Cyano-9H-carbazole. (62%) mp 248e249 ꢀC; 1H NMR
(500 MHz,DMSO-d6):
d 10.68 (s, 1H), 8.39e8.37 (m, 2H), 8.30e8.25
4.2.2. 2b: 2-Methyl-9H-carbazole.7d (85%) mp 174e175 ꢀC; 1H NMR
(500 MHz, CDCl3):
8.06 (d, J¼8.0 Hz, 1H), 7.95 (d, J¼8.0 Hz, 1H),
7.86 (br s, 1H), 7.39e7.38 (m, 2H), 7.26e7.20 (m, 2H), 7.07 (d,
(m, 1H), 8.08e8.05 (m, 1H), 7.64e7.62 (m, 1H), 7.58e7.57 (m, 1H),
7.30e7.28 (m, 1H); 13C NMR (125 MHz,DMSO-d6): 167.5, 146.2,
142.5, 138.8, 128.7, 126.2, 124.3, 121.8, 120.4, 119.1, 114.2, 110.8,
d