Formation of 5-Hydroxy-3-methoxy-1,4-naphthoquinone and 8-Hydroxy-4-methoxy-1,2-naphthoquinone from Juglone

Table 1

¹H and ¹³C NMR data for 3-methoxy juglone (6) and 8-hydroxy-4-methoxy-1,2-naphthoquinone (7) in CDCl₃ at 25°C.

	3-Methoxy juglone (6)				8-Hydroxy-4-methoxy-1,2-naphthoquinone (7)
Pos.	𝛿^a/ppm				𝛿^a/ppm
	^13C	^1H^b	Multiplicity	J(^1H,^1H)^b,c/Hz	^13C	^1H^b	Multiplicity	J(^1H,^1H)^b,d/Hz
1	183.95	—			168.15	—
2	110.50	6.160	qt	−0.41 (O-Me)	103.00	5.955	s	0.35 (O-Me), 0.23 (H-8), 0.18 (H-6)
3	160.08	—			179.06	—
4	184.94	—			182.97	—
4a	114.28	—			113.87	—
5	161.98	11.750	dist. d	0.43 (H-7), 0.03 (H-6)	164.87	12.057	d	0.48 (H-7)
6	123.87	7.246	ho m	8.48 (H-7), 1.09 (H-8), 0.03 (HO-5)	122.43	7.138	ddd	8.61 (H-7), 1.01 (H-8), 0.18 (H-2)
7	137.20	7.640	ho m	8.48 (H-6), 7.45 (H-8), 0.43 (HO-5)	138.14	7.588	ddd	8.61 (H-6), 7.54 (H-8), 0.48 (HO-5)
8	118.95	7.630	ho m	7.45 (H-7), 1.09 (H-6)	117.51	7.411	ddd	7.54 (H-7), 1.01 (H-6), 0.23 (H-2)
8a	132.06	—			131.81	—
CH3O	56.61	3.920	d	−0.41 (H-2)	56.83	3.994	d	0.35 (H-2)

d: doublet; dist.: distorted; ho: higher order; m: multiplet; qt: quartet; s: singlet. ^a1H and ¹³C spectra referenced internally to TMS (𝛿=0.00 ppm for both nuclei). ^bChemical shifts and coupling constants extracted using the Perch simulation software [12, 13]. ^cCouplings in the aromatic ring were determined to be positive from higher-order analysis and were consistent with signs from DFT calculations except for ⁴𝐽_H6,HO5 which was also found to be positive by spin simulation. Despite its small value, ⁴𝐽_H6,HO5 was evident in the lineshape. ⁵𝐽_H2,OMe determined to be negative by DFT calculations. ^d4𝐽_H6,H8 and ⁵𝐽_HO5,H7 were set positive in analogy with 6 and were consistent with signs from DFT calculations. Signs of ⁵𝐽_H2,H8, ⁵𝐽_H2,OMe, and ⁷𝐽_H2,H6 assigned by DFT calculations.