1
038
CHEN ET AL.
closed at top with an anhydrous CaCl tube, and a nitrogen inlet, was
2
charged with phosphyl oxochloride (24.6 g, 160 mmole, 1.1 mol equiv.).
The stirrer was started and the flask was chilled by an ice-salt bath while
nitrogen was introduced. Then a mixture of 3,4-dimethyl-1H-pyrrole
(
5, 13.86 g, 146 mmol) in dry dichloromethane (200 ml) containing dry
N,N-dimethylformamide (13 g, 198 mmol, 1.3 mol equiv.) was added. The
reaction mixture was stirred at room temperature overnight. After removing
all solvent under vacuum, the residue was mixed with water (120 ml). To the
stirred mixture sodium hydroxide (36.8 g, 920 mmol) was added slowly.
Next, the mixture was allowed to stir 1 h at room temperature, the yellow
precipitate was collected, washed with water, and dried to afford the
ꢁ
ꢁ
expected product 6 (13 g, 73%). m.p. 132–134 C (lit [13] 133–134 C).
1
H NMR (300 MHz chloroform-d): d 2.0 (s, 3H, pyrr-CH ), 2.3 (s, 3H,
3
pyrr-CH ), 6.8 (s, 1H, pyrr-H), 9.2 (br s, 1H, NH), 9.6 (s, 1H, CHO)
1
3
3
ppm. C NMR (chloroform-d): d 9.8 (pyrr-CH ), 10.0 (pyrr-CH ), 121.1,
3
3
122.1, 124.2, 127.8, 178.2 ppm.
3,4-Dimethyl-3-pyrrolin-2-one [7, C H NO]: 3,4-Dimethyl-1H-pyrrole
5, 17.0 g, 0.18 mol) was dissolved in pyridine (30 ml) under nitrogen pro-
6
9
(
tection. Then 30% hydrogen peroxide (27 ml, 0.45 mol) was added at once.
ꢁ
The mixture was stirred at 50 C for 2 h. Solvent was removed under vacuum
to give a light orange oil which solidified on drying under vacuum overnight.
The crude product was crystallized from dichloromethane-hexane to give
ꢁ
ꢁ
the desired product 7 (15.9 g, 80%). m.p. 114–116 C (lit [13] 116–118 C) IR
KBr, film): n ¼ 3320, 3100, 2945, 1601, 1545, 1480, 1449, 1320, 1155, 1080,
(
8
À1
þ
1
10, 750, 699 cm . GC-MS: m/z ¼ 111 (M ). H NMR (300 MHz CDCl ): d
3
1
.8 (s, 3H, pyrr-CH ), 2.0 (s, 3H, pyrr–CH ), 3.8 (s, 2H, CH ), 7.3 (br s, 1H,
3
3
2
NH) ppm. C NMR (50 MHz, CDCl ), d 7.8, 9.3, 47.3, 126.5, 154.5,
3
176.3 ppm.
2
,3,7,8-Tetramethyldipyrrinone [8, C H N O]: In a 250-ml three-
1
3
16
2
necked round-bottomed flask, equipped with a nitrogen inlet, a condenser,
and a magnetic stirrer, were charged with 2-formyl-3,4-dimethyl-1H-pyrrole
(
6, 6.0 g, 48 mmol), 3,4-dimethyl-3-pyrrolin-2-one (7, 5.8 g, 52 mmol,
1
1
.09 mol equiv.), aqueous potassium hydroxide (4 M, 150 ml, 0.60 mol,
2.5 mol equiv.) and methanol (125 ml). The suspension was stirred at
reflux for 10 h under nitrogen (a yellow precipitate was formed during
reflux). Solvents were evaporated, the yellow precipitate was collected by
filtration, washed with water and dried to give the expected title compound 8
ꢁ
as yellow powder (7.8 g, 75%). m.p. 268–270 C (dec.) (lit [9b] m.p.
ꢁ
2
1
(
71–273 C). IR (KBr, film): n ¼ 3350, 3200, 3151, 2932, 1596, 1501, 1436,
À1
þ
236, 1175, 1103, 945, 800 cm . MS (FAB): m/z ¼ 216 (M ). UV–Vis
1
Chloroform): lmax(e) ¼ 394 (25 300) nm. H NMR (300 MHz, chloroform-
d): d 1.5 (s, 3H, pyrr–CH ), 1.9 (s, 3H, pyrr–CH ), 2.0 (s, 3H, pyrr-CH ), 2.1
3
3
3