Organic & Biomolecular Chemistry
Paper
Na2SO4 and filtered. The filtrate was concentrated in vacuo and
the obtained residue was purified by silica gel column chrom-
atography (EA/hexane) to afford desired product 3.
Synthesis of 3H-indoles 5. To a 15 mL sealed tube was
added 4 (0.50 mmol), CBr4 (0.75 mmol), K2CO3 (1.00 mmol)
and dry DMSO (5 mL). The resulting mixture was heated at
110 °C for the indicated time until the complete consumption
of starting material as monitored by TLC or GC-MS analysis.
After cooling, the reaction mixture was filtered through a pad
of Celite and the filter cake was washed with EA. The organic
phase was then washed successively with water (3 × 25 mL)
and brine (3 × 25 mL), dried over anhydrous Na2SO4 and fil-
tered. The filtrate was concentrated in vacuo and the obtained
residue was purified by silica gel column chromatography (EA/
hexane) to afford desired product 5.
Scheme 5 Scale-up experiments.
Conclusions
Conflicts of interest
In summary, we have developed a general method for the syn-
thesis of 1H-indoles and 3H-indoles, two important families of
nitrogen-containing heterocycles whose efficient synthesis are
still in high demand. Unlike the previous examples of intra-
molecular cross dehydrogenative coupling of N-aryl enamines,
this process does not require the use of a transition metal or a
stoichiometric amount of oxidant, making it a envirionment-
friendly complement to the existing strategies for the synthesis
of indole derivatives. Moreover, the synthesis of brominated
indoles under subtly adjusted reaction conditions is more
straightforward than that in our previous work.
The authors declare no conflict of interest.
Acknowledgements
This work is financially supported by the Science & Technology
Development Fund of Tianjin Education Commission for
Higher Education (2017KJ138).
Notes and references
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Experimental section
General experimental procedures
Synthesis of 1H-indoles 2. To a 15 mL sealed tube was
added 1 (0.50 mmol), CBr4 (0.75 mmol), K2CO3 (1.00 mmol)
and dry DMSO (5 mL). The resulting mixture was heated at
100 °C for the indicated time until the complete consumption
of starting material as monitored by TLC or GC-MS analysis.
After cooling, the reaction mixture was filtered through a pad
of Celite and the filter cake was washed with EA. The organic
phase was then washed successively with water (3 × 25 mL)
and brine (3 × 25 mL), dried over anhydrous Na2SO4 and fil-
tered. The filtrate was concentrated in vacuo and the obtained
residue was purified by silica gel column chromatography (EA/
hexane) to afford desired product 2.
Synthesis of brominated 1H-indoles 3. To a 15 mL sealed
tube was added 1 (0.50 mmol), CBr4 (1.50 mmol) and dry
DMSO (5 mL). The mixture was stirred at room temperature
and then EtONa (1.00 mmol) was added. The resulting
mixture was heated at 100 °C for the indicated time until the
complete consumption of starting material as monitored by
TLC or GC-MS analysis. After cooling, the reaction mixture was
filtered through a pad of Celite and the filter cake was washed
with EA. The organic phase was then washed successively with
water (3 × 25 mL) and brine (3 × 25 mL), dried over anhydrous
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