European Journal of Organic Chemistry
10.1002/ejoc.201801335
COMMUNICATION
To demonstrate the practical aspect of described
methodology, 5-methoxy indole derivative 6h has been used in
the formal synthesis of (-)-Vincorine (Scheme 3). This sequence
involved oxygenation of indole derivative 6h followed by nitro aldol
condensation to indole 10 in 17 % total yield. Additionally in situ
reduction of double and nitro group, followed by Boc protection of
primary amine gave compound 11 in total 20 % yield, directly used
by McMillan group in synthesis of (-)-Vincorine.[14]
(0.04 mmol, 0.20 equiv.) in MeCN (1 mL) was stirred for 16 h under oxygen
atmosphere and irradiated through the vial’s using blue LEDs. Solvent was
evaporated and the residue was submitted to column chromatography to
afford pure product.
Acknowledgements
The authors gratefully acknowledge financial support from the
National Science Centre, Poland 2012/07/D/ST5/02313 (MS) and
2
016/23/N/ST5/00117 (FS). JM thanks the Polish National
Science Centre for financial support (MAESTRO Grant Nr.
013/10/A/ST5/00233).
2
Keywords: photocatalysis • Brønsted acids • photoredox •
oxygenation • indole
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Scheme 3. Formal Synthesis of (-)-Vincorine.
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2
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Typical procedure for the synthesis of 6: 1-Methyl-3-
dimethylaminomethyleneindole and their derivatives were prepared
according to modified literature procedure 1: A mixture of the formaldehyde
3
6 % solution in water (9.2 mmol, 1.15 equiv.), glacial acetic acid (32.0
mmol, 4.0 equiv.) and 40 % solution of dimethylamine in water (9.2 mmol,
.15 equiv.) were added together and stirred for 30 min. After specified
1
time to the reaction mixture 5 mL DCM was added and stirred for next 15
min and then N-methyl indole (8.0 mmol, 1.0 equiv.) in 5 mL DCM was
added. The reaction was stirred for 16 h and quenched by 5 mL 4 M NaOH.
The oil was extracted 3 times with diethyl ether and combined organic
layers were washed with brine and then dried over anhydrous MgSO .
4
After removal of the drying agent by filtration, the filtrate was concentrated
by vacuum evaporation giving pure product.
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Typical
Dimethylaminomethylene)-N-Alkylindoles derivative 6a-p (0.200 mmol,
.00 equiv.), [Ru(bpy) ](PF (0.004 mmol, 0.02 equiv.), benzoic acid
procedure
for
the
synthesis
of
7:
3-(N,N-
1
3
6 2
)
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