Supporting Information

L-Proline catalyzed condensation of salicylaldehydes with ethyl nitroacetate: An efficient access to 3-nitrocoumarins

Rajesh Kumar Sharma,1 Priyanka,1 Diksha Katiyar1*

1Department of Chemistry, MMV, Banaras Hindu University, Varanasi-221005, India

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1. Experimental 2

2. Procedure for the synthesis of ethyl nitroacetate 2

3. Spectral data of representative compounds 3-13

1

1. Experimental

Unless otherwise stated, all common reagents and solvents were obtained from commercial suppliers

(Sigma-Aldrich and Spectrochem Pvt. Ltd.) and were used without further purification. Melting points

were determined on a Buchi 510 apparatus and are uncorrected. Column chromatography was carried on

silica gel (60-120 mesh). Reactions were monitored by thin-layer chromatography (TLC) using pre-

coated, glass-backed silica gel plates and visualization of the developed chromatogram was performed

by UV absorbance (254 nm) and by iodine vapours. ESI mass spectra were recorded using Quattro II

(Micromass). IR spectra were recorded on a JASCO FTIR 5300 in KBr from 400-4000 cm−1. NMR

spectra were recorded on JEOL FT-NMR spectrometer using tetramethylsilane (TMS) as internal

standard. The chemical shift values are on δ scale and the coupling constant (J) are in hertz (Hz). The

data of 1H NMR was reported in the order: chemical shift, multiplicity (s = singlet, d = doublet, t =

triplet, m = multiplet and br = broad), coupling constant and integration.

2. Procedure for the synthesis of ethyl nitroacetate (2)

In a first step, a solution of NaNO2 (1.8 g, 25.71 mmol) in water (2.5 mL) was added to a mixture of

ethylacetoacetate (3 mL, 23.51mmol) and AcOH (4 mL) at 5-15 °C with constant stirring. The resulting

mixture was stirred at 15 °C for 1 h and then poured into 60 mL ice cold water. The suspension was kept

for 16 h and extracted with chloroform. The organic layer was dried over anhydrous Na2SO4 and

evaporated under reduced pressure to afford isonitrosoacetoacetate as an oily residue (2.5 g). In a second

step, a solution of potassium dichromate (4.52 g, 15.6 mmol), water (10 mL) and concentrated H2SO4

(3.75 mL) was added to a suspension of isonitrosoacetoacetate (2.5 g) in water (6 mL). The resulting

mixture was stirred for 6 h at 20oC and then poured into 10 mL of ice cold water and heated to room

temperature. The suspension obtained was extracted with chloroform. The organic layer was neutralized

by saturated solution of sodium bicarbonate, washed with brine solution, dried over anhydrous Na2SO4

and evaporated to furnish ethyl nitroacetate 2 as oil in 65% yield (reported: 39% [30]).

2

3. Spectral data of representative compounds

IR spectrum of 3-nirocoumarin (3)

3

1H NMR spectrum of 3-nirocoumarin (3)

4

13C NMR spectrum of 3-nirocoumarin (3)

5

1H NMR spectrum of 6-methyl-3-nitrocoumarin (5b)

13C NMR spectrum of 6-methyl-3-nitrocoumarin (5b)

6

IR spectrum of 6-chloro-3-nitrocoumarin (5e)

7

1H NMR spectrum of 6-chloro-3-nitrocoumarin (5e)

8

13C NMR spectrum of 6-chloro-3-nitrocoumarin

9

IR spectrum of 2-nitro-3H-benzo[f]chromen-3-one (5h)

10

11

1H NMR spectrum of 2-nitro-3H-benzo[f]chromen-3-one (5h)

13C NMR spectrum of 2-nitro-3H-benzo[f]chromen-3-one (5h)

12

13