7-Chloro-4-formyl-2-salicyloyl-9H-xanthen-9-one 19c. From
1c in 18% yield; mp 240 ЊC (Found: C, 66.2; H, 2.7. C21H11ClO5
requires C, 66.6; H, 2.9%); δH 11.74 (1H, s, exchangeable, OH),
10.83 (1H, s, CHO), 8.89 (1H, d, J 2.4, 1- or 3-H), 8.64 (1H, d,
J 2.4, 3- or 1-H), 8.34 (1H, d, J 2.6, 8-H), 7.80 (1H, dd, J 8.8
and 2.6, 6-H), 7.64 (1H, d, J 8.8, 5-H), 7.59 (1H, ddd, J 8.5,
7.8 and 1.6, 4Ј-H), 7.52 (1H, dd, J 8.0 and 1.6, 6Ј-H), 7.13 (1H,
dd, J 8.5 and 0.9, 3Ј-H) and 6.94 (1H, m, 5Ј-H).
2,3-Bis(methoxycarbonyl)-1-phenyl-9H-xanthen-9-ones 36.
General procedure
A benzoylenaminone 3 was allowed to react with an equimolar
amount of DMAD 27 in refluxing DMF similarly as described
for the treatment of 1 with DMAD. The brown solid mass
obtained after usual work-up of the reaction mixture was crys-
tallised twice from chloroform–light petroleum to afford the
corresponding title xanthenone 36 (Tables 5 and 6).
Treatment of enamines 1 with acid 15
Treatment of enamines 1 with ethyl propiolate (EP) 29
An enamine 1 was treated with the acid 15 similarly as
described for treatment of 1 with the aldehyde 14. The solid
that precipitated after cooling of the reaction mixture and sub-
sequent dilution with water was filtered off, dried, and crystal-
lised from chloroform (charcoal)–light petroleum to afford
the corresponding xanthenone 18. The xanthenones 18a,b,c
were obtained in 40, 35 and 37% yield from the enamines
1a,b,c, respectively.
A mixture of an enamine 1 (1 mmol) and EP (0.3 ml, ≈3 mmol)
in DMF (15 ml) was heated under reflux for 8 h. The reaction
mixture was then concentrated, cooled, diluted with water and
extracted with chloroform. The chloroform extract was concen-
trated, and chromatographed over silica using a 1:10 mixture
of ethyl acetate and light petroleum as eluent, when the benzene-
tricarboxylate 46 (2–4%), the corresponding xanthenone 37
(26–35%) and the corresponding flavone 43 (5–7%) were eluted
in that order. The expected flavone 43a could not be obtained
from the reaction mixture of 1a and EP. Triethyl benzene-1,3,5-
tricarboxylate 46 had mp 134 ЊC (lit.,18 135–136 ЊC); δH 8.84
(3H, s, ArH), 4.43 (6H, q, OCH2Me) and 1.43 (9H, t, OCH2-
Me); δC 165.1 (ester CO), 134.4 (phenyl C-H), 131.7 (phenyl
carbon linked to CO2Et), 61.6 (OCH2Me) and 14.3 (Me); m/z
294 (Mϩ, 18%), 266 (M Ϫ C2H4, 34), 249 (M Ϫ OEt, 100), 238
(266 Ϫ C2H4, 34), 221 (249 Ϫ CO, 68), 210 (238 Ϫ C2H4, 32),
193 (221 Ϫ C2H4, 38), 176 (193 Ϫ OH, 12), 165 (193 Ϫ C2H4,
16) and 148 (193 Ϫ OEt, 18). The following xanthenones 37 and
flavones 43 were obtained by this procedure.
Treatment of enamines 1a,b with nitrile 16: synthesis of 3-(4-oxo-
4H-1-benzopyran-2-yl)[1]benzopyrano[2,3-b]pyridines 26.
General procedure
An enamine 1 (0.5 mmol) and the nitrile 16 (85.5 mg, 0.5 mmol)
were refluxed together in DMF (20 ml) for 7 h. The reaction
mixture was concentrated, cooled, diluted with water and the
deposited solid was filtered off. This was dried, and crystallised
from chloroform–light petroleum. By this procedure the follow-
ing compounds were prepared.
26a. Yellow solid (16%) from 1a; mp >282 ЊC (Found: C,
74.2; H, 2.9; N, 4.4. C21H11NO4 requires C, 73.9; H, 3.2; N,
4.1%); δH 9.28 (1H, d, J 2.6, 1-H), 9.24 (1H, d, J 2.6, 3-H), 8.38
(1H, dd, J 8.0 and 1.7, 5Ј-H), 8.26 (1H, dd, J 8.0 and 1.5, 9-H),
7.86 (1H, ddd, J 8.0, 7.2 and 1.6, 7Ј-H), 7.76 (1H, ddd, J 8.0, 7.2
and 1.5, 7-H), 7.73–7.38 (4H, m, other ArH) and 6.97 (1H, s,
3Ј-H).
26b. Yellow solid (18%) from 1b; mp >282 ЊC (Found: C,
74.0; H, 3.3; N, 4.2. C22H13NO4 requires C, 74.4; H, 3.7; N,
3.9%); δH 9.26 (1H, d, J 2.5, 1-H), 9.22 (1H, d, J 2.5, 3-H), 8.37
(1H, dd, J 7.6 and 1.7, 9-H), 8.04 (1H, d, J 1.8, 5Ј-H), 7.85 (1H,
ddd, J 7.6, 7.2 and 1.6, 7-H), 7.78 (1H, dd, J 8.0 and 1.5, 7Ј-H),
7.56–7.47 (3H, other ArH), 6.94 (1H, s, 3Ј-H) and 2.50 (3H, s,
6Ј-Me).
Ethyl 9-oxo-9H-xanthene-2-carboxylate 37a. From 1a in 35%
yield; mp 152 ЊC (Found: C, 71.4, H, 4.2. C16H12O4 requires C,
71.6; H, 4.5%); δH 9.01 (1H, d, J 2.2, 1-H), 8.38 (1H, dd, J 8.8
and 2.2, 3-H), 8.35 (1H, dd, J 9.1 and 1.7, 8-H), 7.75 (1H, ddd,
J 7.3, 7.2 and 1.7, 6-H), 7.55–7.39 (3H, m, other ArH), 4.43
(2H, q, OCH2Me) and 1.43 (3H, t, CH2Me).
Ethyl 7-methyl-9-oxo-9H-xanthene-2-carboxylate 37b. From
1b in 28% yield; mp 148 ЊC (Found: C, 71.9; H, 5.2. C17H14O4
requires C, 72.3; H, 5.0%); δH 9.00 (1H, d, J 2.1, 1-H), 8.35 (1H,
dd, J 8.8 and 2.1, 3-H), 8.11 (1H, poorly split d, 8-H), 7.55 (1H,
dd, J 8.6 and 2.0, 6-H), 7.51 (1H, d, J 8.8, 4-H), 7.40 (1H, d,
J 8.6, 5-H), 4.42 (2H, q, OCH2Me), 2.41 (3H, s, 7-Me) and 1.46
(3H, t, CH2Me). 13C NMR data are given in Table 6.
General procedure for treatment of dienamines 1 with DMAD 27
and with dibenzoylacetylene 28
A solution of a dienamine 1 (2 mmol) and DMAD 27 (2 mmol,
≈0.4 ml) in DMF (15 ml) was heated under reflux for 5 h. Usual
work-up of the reaction mixture gave a brown solid, which on
crystallisation from chloroform (charcoal)–light petroleum
afforded the corresponding 2,3-bis(methoxycarbonyl)-9H-
xanthen-9-one 33. Similar treatment of a dienamine 1 with an
equimolar amount of dibenzoylacetylene 28 yielded the corre-
sponding 2,3-dibenzoyl-9H-xanthen-9-one 34. Tables 5 and 6
contain the characterisation data of xanthenones 33 and 34.
Ethyl 7-chloro-9-oxo-9H-xanthene-2-carboxylate 37c. From
1c in 26% yield; mp 146 ЊC (Found: C, 63.6; H, 3.9. C16H11ClO4
requires C, 63.5; H, 3.7%); νmax (KBr)/cmϪ1 1730 (ester CO),
1675 (keto CO); δH 9.05 (1H, d, J 2.1, 1-H), 8.40 (1H, dd, J 8.8
and 2.1, 3-H), 8.31 (1H, d, J 2.6, 8-H), 7.70 (1H, dd, J 8.9 and
2.6, 6-H), 7.55 (1H, d, J 8.8, 4-H), 7.49 (1H, d, J 8.9, 5-H), 4.43
(2H, q, OCH2Me) and 1.44 (3H, t, CH2Me).
3Ј,5Ј-Bis(ethoxycarbonyl)-6-methylflavone 43b. Colourless
crystals (5%) from 1b, mp 171 ЊC (Found: C, 69.7; H, 5.5.
C22H20O6 requires C, 69.5; H, 5.3%); δH 8.81 (1H, t, J 1.5, 4Ј-H),
8.75 (2H, d, J 1.5, 2Ј-, 6Ј-H), 8.03 (1H, poorly split d, 5-H),
7.55 (2H, m, 7-, 8-H), 6.94 (1H, s, 3-H), 4.48 (4H, q, J 7.2,
2 × OCH2Me), 2.49 (3H, s, 6-Me) and 1.46 (6H, t, J 7.2, 2 ×
CH2Me).
Treatment of dienamines 2 with DMAD 27
A solution of a dienamine 2 (1 mmol) and DMAD 27 (1 mmol,
≈0.2 ml) in DMF (20 ml) was refluxed for 4 h, the solution
becoming progressively darker in colour on refluxing. The solu-
tion was concentrated, cooled, and diluted with water, when an
oily mass separated out. This was extracted with chloroform
and the solid obtained therefrom was subjected to fractional
crystallisation from chloroform–light petroleum, when the
corresponding xanthenone 35 (Tables 5 and 6) first crystallised
out, followed by the corresponding lesser homologue 33 (9–
15%). The mother liquor left after obtention of the aforesaid
two xanthenones was further concentrated and subsequently
diluted with light petroleum to afford the corresponding 1-
hydroxyxanthenone 11 (4–7%).
6-Chloro-3Ј,5Ј-bis(ethoxycarbonyl)flavone 43c. Colourless
crystals (7%) from 1c, mp 160 ЊC (Found: C, 63.1; H, 4.2.
C21H17ClO6 requires C, 62.9; H, 4.3%); δH 8.83 (1H, t, J 1.4,
4Ј-H), 8.74 (2H, d, J 1.4, 2Ј-, 6Ј-H), 8.21 (1H, d, J 2.5, 5-H),
7.70 (1H, dd, J 9.0 and 2.5, 7-H), 7.63 (1H, d, J 9.0, 8-H), 6.96
(1H, s, 3-H), 4.41 (4H, q, 2 × OCH2Me) and 1.46 (6H, t, 2 ×
CH2Me).
3012
J. Chem. Soc., Perkin Trans. 1, 1999, 3005–3013